Digestion and absorption of carbohydrates | My Assignment Tutor

96CHAPTER OUTLINETHE CHEMIST’S VIEW OF CARBOHYDRATESThe simple carbohydrates• Monosaccharides• DisaccharidesThe complex carbohydrates• Glycogen• Starches• FibreDigestion and absorption of carbohydrates• Carbohydrate digestion• Carbohydrate absorption• Lactose intoleranceGlucose in the body• A preview of carbohydrate metabolism• The constancy of blood glucoseHealth effects and recommended intakesof sugars• Health effects of sugars• Recommended intakes of sugarsAlternative sweeteners• Artificial sweeteners• Stevia … Continue reading “Digestion and absorption of carbohydrates | My Assignment Tutor”

96CHAPTER OUTLINETHE CHEMIST’S VIEW OF CARBOHYDRATESThe simple carbohydrates• Monosaccharides• DisaccharidesThe complex carbohydrates• Glycogen• Starches• FibreDigestion and absorption of carbohydrates• Carbohydrate digestion• Carbohydrate absorption• Lactose intoleranceGlucose in the body• A preview of carbohydrate metabolism• The constancy of blood glucoseHealth effects and recommended intakesof sugars• Health effects of sugars• Recommended intakes of sugarsAlternative sweeteners• Artificial sweeteners• Stevia – a herbal product• Sugar alcohols4CHAPTERNutrition in your lifeWhether you are cramming for an exam or daydreaming about your next holiday, yourbrain needs carbohydrate to power its activities. Your muscles need carbohydrate tofuel their work, too, whether you are racing to get to class on time or enjoying a swimin the summer warmth. Where can you get carbohydrate? Are some foods healthierchoices than others? As you will learn from this chapter, whole grains, vegetables,legumes and fruits naturally deliver ample carbohydrate and fibre with valuablevitamins and minerals and little or no fat. Milk products typically lack fibre, but theyalso provide carbohydrate along with an assortment of vitamins and minerals.THE CARBOHYDRATES: SUGARS,STARCHES AND DIETARY FIBREPUTTING COMMONSENSE TO THE TESTCircle your answer T FComplex carbohydrates are long chains of monosaccharides joined together.T FThe majority of carbohydrate digestion occurs in the large intestine.T FPeople who suffer lactose intolerance must avoid all dairy foods.T FGlucose fuels the majority of the body’s energy needs. Throughout thischapter, theCourseMate logoindicates anopportunity foronline self-study,linking you toactivities, videosand other onlineresources.• Figure 4.10:Animated!Carbohydratedigestion in theGI tract• Nutritionportfolio journal• Nutritioncalculations:Practice problemsEleanor, Whitney, et al. Understanding Nutrition, Cengage Australia, 2016. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/think/detail.action?docID=5024519.Created from think on 2021-03-22 18:34:59.Copyright © 2016. Cengage Australia. All rights reserved.A student, quietly studying a textbook, is seldom aware that within their brain cells, billions ofglucose molecules are splitting to provide the energy to permit learning. Yet glucose providesnearly all of the energy the human brain uses daily. Similarly, a marathon runner, burstingacross the finish line in an explosion of sweat and triumph, seldom gives credit to the glycogenfuel that is devoured to help them finish the race. Yet, together, these two carbohydrates –glucose and its storage form, glycogen – provide about half of all the energy that muscles andother body tissues use. The other half of the body’s energy comes mostly from fat.People eat very little glucose and glycogen in their foods directly. When they eat foods richin carbohydrates, their bodies receive glucose for immediate energy and convert the remainderinto glycogen for reserve energy. All plant foods – whole grains, vegetables, legumes and fruits –provide ample carbohydrate. Milk also contains carbohydrates.Many people mistakenly think of carbohydrates as ‘fattening’ and avoid them when tryingto lose weight. Such a strategy may be helpful if the carbohydrates are the simple sugars of softdrinks, lollies (candy) and biscuits (cookies), but it is counterproductive if the carbohydrates arethe complex carbohydrates of whole grains, vegetables and legumes. As the next section explains,not all carbohydrates are created equal.THE CHEMIST’S VIEW OF CARBOHYDRATESLEARN ITIdentify the monosaccharides, disaccharides, and polysaccharides common in nutrition by theirchemical structures and major food sources.The dietary carbohydrate family includes the simple carbohydrates (the sugars) and thecomplex carbohydrates (the starches and fibre). The simple carbohydrates are those thatchemists describe as:• monosaccharides – single sugars• disaccharides – sugars composed of pairs of monosaccharides.The complex carbohydrates are:• polysaccharides – large molecules composed of chains of monosaccharides.Each atom can form a certain number of chemical bonds with other atoms:• carbon atoms can form four bonds• nitrogen atoms, three• oxygen atoms, two• hydrogen atoms, only one.Chemists represent the bonds as lines between the chemical symbols (such as C,N, O and H) that stand for the atoms (see Figure 4.1).Atoms form molecules in ways that satisfy the bonding requirements of eachatom. Figure 4.1 includes the structure of ethyl alcohol, the active ingredientof alcoholic beverages, as an example. The two carbons each have four bondsrepresented by lines, the oxygen has two, and each hydrogen has one bondconnecting it to other atoms. Chemical structures bond according to these rulesas dictated by nature.Health effects and recommended intakes of starchand dietary fibre• Health effects of starch and dietary fibre• Recommended intakes of starch and dietary fibre• From guidelines to groceriesHighlight 4: Carbs, kJ and controversiesH 1O 2N 3C 4Each atom has a characteristic numberof bonds it can form with other atoms.H C ONotice that in this simple molecule ofethanol (or alcohol), each H has onebond, O has two and each C has four.C HH HH HFIGURE 4.1 Atoms and their bondsThe four main types of atoms found innutrients are hydrogen (H), oxygen (O),nitrogen (N) and carbon (C).CHAPTER 4 THE CARBOHYDRATES: SUGARS, STARCHES AND DIETARY FIBRE 97Eleanor, Whitney, et al. Understanding Nutrition, Cengage Australia, 2016. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/think/detail.action?docID=5024519.Created from think on 2021-03-22 18:34:59.Copyright © 2016. Cengage Australia. All rights reserved.THE SIMPLE CARBOHYDRATESThe carbohydrates are made of carbon (C), oxygen (O) and hydrogen (H). Each of these atoms can forma specified number of chemical bonds: carbon forms four, oxygen forms two and hydrogen forms one.REVIEW IT LEARN ITIdentify the three important monosaccharides and three important disaccharides in the human diet.The following list of the most important simple carbohydrates in nutrition symbolises them ashexagons and pentagons of different colours. Three are monosaccharides:• glucose• fructose• galactoseThree are disaccharides:• maltose (glucose 1 glucose)• sucrose (glucose 1 fructose)• lactose (glucose 1 galactose)To understand the structure of carbohydrates, look at the units of which they are made. Themonosaccharides most important in nutrition* each contain 6 carbon atoms, 12 hydrogens and6 oxygen atoms (written in shorthand as C6H12O6).MONOSACCHARIDESThe three monosaccharides important in nutrition all have the same numbers and kinds of atoms,but in different arrangements. These chemical differences account for the differing sweetness of themonosaccharides. A pinch of purified glucose on the tongue gives only a mild sweet flavour,and galactose hardly tastes sweet at all. Fructose, however, is as intensely sweet as honey and,in fact, is the sugar primarily responsible for honey’s sweetness.GlucoseChemically, glucose is a larger and more complicated molecule than the ethanol(alcohol) shown in Figure 4.1, but it obeys the same rules of chemistry: each carbonatom has four bonds; each oxygen, two bonds; and each hydrogen, one bond. Figure 4.2illustrates the chemical structure of a glucose molecule.The diagram of a glucose molecule shows all the relationships between the atomsand proves simple on examination, but chemists have adopted even simpler ways todepict chemical structures. Figure 4.3 presents the chemical structure of glucose in amore simplified way by combining or omitting several symbols – yet it conveys the sameinformation.Commonly known as blood sugar, glucose serves as an essential energy source for allthe body’s activities. Its significance to nutrition is tremendous. Later sections explainthat glucose is one of the two sugars in every disaccharide and the unit from whichthe majority of polysaccharides are made. One of these polysaccharides, starch, is thechief food source of energy for all the world’s people; another, glycogen, is an importantMost of themonosaccharidesimportant in nutrition arehexoses, simple sugarswith six atoms of carbonand the formula C6H12O6• hex 5 six*Fructose is shown as a pentagon, but like the other monosaccharides, it has six carbons (as you will see in Figure 4.4;see page 99).HHH OHH OH HHH O HO HO HCCC CCCOFIGURE 4.2 Chemical structureof glucoseOn paper, the structure of glucosehas to be drawn flat, but in naturethe five carbons and oxygen areroughly in a plane. The atomsattached to the ring carbonsextend above and below the plane.98 UNDERSTANDING NUTRITIONEleanor, Whitney, et al. Understanding Nutrition, Cengage Australia, 2016. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/think/detail.action?docID=5024519.Created from think on 2021-03-22 18:34:59.Copyright © 2016. Cengage Australia. All rights reserved.storage form of energy in the body. Glucose reappears frequently throughout this chapter andall those that follow.FructoseFructose is the sweetest of the sugars. Curiously, fructose has exactly the same chemicalformula as glucose – C6H12O6 – but its structure differs (see Figure 4.4). The arrangementof the atoms in fructose stimulates the taste buds on the tongue to produce the sweet sensation.Fructose occurs naturally in fruits and honey; other sources include products such as some softdrinks, ready-to-eat cereals and desserts, particularly those imported into Australia and NewZealand that have been sweetened with high-fructose corn syrup (defined on page 115).GalactoseThe monosaccharide galactose occurs naturally as a single sugar in only a few foods. Galactosehas the same numbers and kinds of atoms as glucose and fructose in yet another arrangement.Figure 4.5 shows galactose beside a molecule of glucose for comparison.OHOHHO OHCH2OHOHH HHHOHOHHO OHCH2OHOOC CC CC CThe lines representing someof the bonds and the carbons atthe corners are not shown.Now the single hydrogens arenot shown, but lines still extendupward or downward from thering to show where they belong.Another way to look at glucose isto notice that its six carbon atomsare all connected.In this and other illustrationsthroughout this book, glucose isrepresented as a blue hexagon.FIGURE 4.3 Simplified diagrams of glucoseOHOHHO OHCH2OHOOHHOOHOHOCH2 CH2OH13 24561 24 356Glucose FructoseFIGURE 4.4 Two monosaccharides: glucose and fructoseCan you see the similarities? If you learned the rules inFigure 4.3, you will be able to ‘see’ 6 carbons (numbered),12 hydrogens (those shown plus one at the end of each singleline) and 6 oxygen atoms in both these compounds.OHOHOHCH2OHOGlucoseHO OHOHOHCH2OHOGalactoseHOFIGURE 4.5 Two monosaccharides: glucose and galactoseNotice the similarities and the difference (highlighted inred) between glucose and galactose. Both have 6 carbons,12 hydrogens and 6 oxygens, but the position of one OH groupdiffers slightly.DISACCHARIDESThe disaccharides are pairs of the three monosaccharides just described. Glucose occurs inall three; the second member of the pair is either fructose, galactose or another glucose. Thesecarbohydrates – and all the other energy nutrients – are put together and taken apart by similarchemical reactions: condensation and hydrolysis.CHAPTER 4 THE CARBOHYDRATES: SUGARS, STARCHES AND DIETARY FIBRE 99Eleanor, Whitney, et al. Understanding Nutrition, Cengage Australia, 2016. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/think/detail.action?docID=5024519.Created from think on 2021-03-22 18:34:59.Copyright © 2016. Cengage Australia. All rights reserved.HydrolysisTo break a disaccharide in two, a chemical reaction known as hydrolysis occurs (seeFigure 4.7). A molecule of water splits to provide the H and OH needed to complete the resultingmonosaccharides. Hydrolysis reactions commonly occur during digestion.Reminder: Ahydrolysis reaction splitsa molecule into two, withH added to one and OHto the other (from water);Chapter 3 explainedthat hydrolysis reactionsbreak down moleculesduring digestion.CondensationTo make a disaccharide, a chemical reaction known as condensation links twomonosaccharides together (see Figure 4.6). A hydroxyl (OH) group from onemonosaccharide and a hydrogen atom (H) from the other combine to create amolecule of water (H2O). The two originally separate monosaccharides link togetherwith a single oxygen (O).OOHOHHOCH2OHOOHOHO OHCH2OHOH H2OWater OHOHHOCH2OHOOHOHOHCH2OHO+Glucose + glucose MaltoseH2OWaterOHThe two glucose molecules bondtogether with a single O atom to formthe disaccharide maltose.An OH group from one glucose and anH atom from another glucose combineto create a molecule of H2O.FIGURE 4.6 Condensation of two monosaccharides to form a disaccharideOHOHHOCH2OHOOHOHOHCH2OHOMaltose Glucose + glucoseOHOHHOCH2OHOOHOHOHCH2OHOOH OHBondbrokenBond broken+WaterThe disaccharide maltose splits into two glucose molecules with H added to one and OH to the other(from the water molecule).OH HOFIGURE 4.7 Hydrolysis of a disaccharideFruits package their simple sugars withfibre, vitamins and minerals, makingthem a sweet and healthy snack.iStockphoto/Ivan BajicMajor sources of starch include grains(such as rice, wheat, millet, rye, barleyand oats), legumes (such as kidneybeans, cannellini beans, peas, chickpeasand lentils), tubers (such as potatoes)and root crops (such as sweet potatoand cassava).Polara Studios, Inc.MaltoseThe disaccharide maltose consists of two glucose units. Maltose is produced wheneverstarch breaks down – as happens in human beings during carbohydrate digestion. Italso occurs during the fermentation process that yields alcohol. Maltose is only aminor constituent of a few foods, most notably barley.100 UNDERSTANDING NUTRITIONEleanor, Whitney, et al. Understanding Nutrition, Cengage Australia, 2016. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/think/detail.action?docID=5024519.Created from think on 2021-03-22 18:34:59.Copyright © 2016. Cengage Australia. All rights reserved.SucroseFructose and glucose together form sucrose. Because the fructose is accessible to the tastereceptors, sucrose tastes sweet, accounting for some of the natural sweetness of fruits, vegetablesand grains. To make table sugar, sucrose is refined from the juices of sugar cane and thengranulated. Depending on the extent to which it is refined, the product becomes the familiarbrown, white and powdered sugars available at supermarkets.LactoseThe combination of galactose and glucose makes the disaccharide lactose, the principalcarbohydrate of milk. Known as milk sugar, lactose contributes half of the energy (kilojoules)provided by fat-free milk.THE COMPLEX CARBOHYDRATESSix simple carbohydrates, or sugars, are important in nutrition. The three monosaccharides (glucose,fructose and galactose) all have the same chemical formula (C6H12O6), but their structures differ. Thethree disaccharides (maltose, sucrose and lactose) are pairs of monosaccharides, each containing aglucose paired with one of the three monosaccharides. These sugars derive primarily from plants,except for lactose and its component galactose, which come from milk and milk products. Twomonosaccharides can be linked together by a condensation reaction to form a disaccharide andwater. A disaccharide, in turn, can be broken into its two monosaccharides by a hydrolysis reactionusing water.REVIEW ITIn contrast to the simple sugars just mentioned, complex carbohydrates contain many glucoseunits and, in some cases, a few other monosaccharides strung together as, firstly, oligosaccharidesand, secondly, as the larger polysaccharides. Three types of polysaccharides are important innutrition: glycogen, starches and fibre.Glycogen is a storage form of energy in the animal body; starches play that role in plants;and fibre provides structure in stems, trunks, roots, leaves and skins of plants. Both glycogen andstarch are built of glucose units. Fibre is composed of a variety of monosaccharides and othercarbohydrate derivatives.GLYCOGENGlycogen is found to only a limited extent in meats and not at all in plants.* For this reason, foodis not a significant source of this carbohydrate. However, glycogen does perform an importantrole in the body. The human body stores glucose as glycogen – many glucose molecules linkedtogether in highly branched chains (see the left-hand side of Figure 4.8). This arrangementpermits rapid hydrolysis. When the hormonal message ‘release energy’ arrives at the glycogenstorage sites in a liver or muscle cell, enzymes respond by attacking the many branches ofglycogen simultaneously, making a surge of glucose available.***Glycogen in animal muscles rapidly hydrolyses after slaughter.**Normally, only liver cells can produce glucose from glycogen to be sent directly to the blood; muscle cells can also produceglucose from glycogen, but must use it themselves. Muscle cells can restore the blood glucose level indirectly, however, asChapter 7 explains.LEARN ITIdentify the three important monosaccharides and three important disaccharides in the humandiet.CHAPTER 4 THE CARBOHYDRATES: SUGARS, STARCHES AND DIETARY FIBRE 101Eleanor, Whitney, et al. Understanding Nutrition, Cengage Australia, 2016. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/think/detail.action?docID=5024519.Created from think on 2021-03-22 18:34:59.Copyright © 2016. Cengage Australia. All rights reserved.STARCHESThe human body stores glucose as glycogen, but plant cells store glucose as starches –long, branched or unbranched chains of hundreds or thousands of glucose moleculeslinked together (see the middle and right-hand side of Figure 4.8). These giant starchmolecules are packed side by side in grains such as wheat or rice, in root crops and tuberssuch as sweet potatoes and potatoes, and in legumes such as lentils and beans. When youeat the plant, your body hydrolyses the starch to glucose and uses the glucose for its ownenergy purposes.All starchy foods come from plants. Grains are the richest food source of starch,providing much of the food energy for people all over the world – rice in Asia; wheat inAustralia, New Zealand, the United States and Europe; corn in much of Central and SouthAmerica; and millet, rye, barley and oats elsewhere. Legumes and tubers are also importantsources of starch.FIBREDietary fibre is the structural parts of plants and thus is found in all plant-derivedfoods – vegetables, fruits, whole grains and legumes. Most dietary fibre is made up ofpolysaccharides. As mentioned earlier, starches are also polysaccharides, but dietary fibrediffers from starches in that the bonds between their monosaccharides cannot be brokendown by digestive enzymes in the body. For this reason, dietary fibres are often describedas non-starch polysaccharides.* Figure 4.9 illustrates the difference in the bonds that linkglucose molecules together in starch with those found in the fibre cellulose. Because dietaryfibre passes through the body, it contributes no monosaccharides, and therefore little orno energy.PUTTINGCOMMONSENSE TOTHE TESTComplexcarbohydratesare long chains ofmonosaccharidesjoined together.TRUE*The non-starch polysaccharide fibres include cellulose, hemicelluloses, pectins, gums and mucilages. Fibres also includesome non-polysaccharides such as lignins, cutins and tannins.Dietary fibre occursnaturally in intactplants. Functional fibreis sometimes usedas a term to describefibre that has beenextracted from plantsor manufactured andhas beneficial effectsin human beings. Inmanufactured foods,total fibre is the sumof dietary fibre andfunctional fibre.Glycogen Starch (amylopectin) Starch (amylose)A glycogen molecule contains hundreds of glucoseunits in highly branched chains. Each new glycogenmolecule needs a special protein for the attachmentof the first glucose (shown here in red).A starch molecule contains hundreds of glucose moleculesin either occasionally branched chains (amylopectin) orunbranched chains (amylose).FIGURE 4.8 Glycogen and starch molecules compared (small segments)Notice the more highly branched the structure, the greater the number of ends from which glucose can be released. (These unitswould have to be magnified millions of times to appear at the size shown in this figure. For details of the chemical structures, seeAppendix C.)102 UNDERSTANDING NUTRITIONEleanor, Whitney, et al. Understanding Nutrition, Cengage Australia, 2016. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/think/detail.action?docID=5024519.Created from think on 2021-03-22 18:34:59.Copyright © 2016. Cengage Australia. All rights reserved.Even though most foods contain a variety of fibre, researchers often sortdietary fibre into two groups according to their solubility. Such distinctions helpto explain their actions in the body.Soluble fibreSome dietary fibre dissolves in water (soluble fibre), forms gels (viscous) andis easily digested by bacteria in the colon (fermentable). Commonly found inoats, barley, legumes and citrus fruits, soluble fibre is most often associated withprotecting against heart disease and diabetes by lowering blood cholesterol andglucose levels, respectively.1Insoluble fibreOther fibre does not dissolve in water (insoluble fibre), does not form gels(non-viscous) and is less readily fermented. Found mostly in whole grains(bran) and vegetables, insoluble fibre promotes bowel movements and alleviatesconstipation.Resistant starchesA few starches are also classified as dietary fibre. Known as resistant starches, thesestarches escape digestion and absorption in the small intestine. Starch may resist digestion forseveral reasons, including the individual’s efficiency in digesting starches and the food’s physicalproperties. Resistant starch is common in whole legumes, raw potatoes and unripe bananas.Phytic acidAlthough not classified as a dietary fibre, phytic acid is often found accompanying them inthe same foods. Because of this close association, researchers have been unable to determinewhether it is the dietary fibre, the phytic acid or both that binds with minerals, preventing theirabsorption. This binding presents a risk of mineral deficiencies, but the risk is minimal whentotal fibre intake is reasonable and mineral intake adequate. The nutrition consequences of suchmineral losses are described further in Chapters 12 and 13.StarchCelluloseFIGURE 4.9 Starch and cellulosemolecules compared (small segments)The bonds that link the glucose moleculestogether in cellulose are different from thebonds in starch (and glycogen). Humanenzymes cannot digest cellulose. SeeAppendix C for chemical structures anddescriptions of linkages.The complex carbohydrates are the polysaccharides (chains of monosaccharides): glycogen, starchesand dietary fibre. Both glycogen and starch are storage forms of glucose – glycogen in the body, andstarch in plants – and both yield energy for human use. Dietary fibre also contains glucose (and othermonosaccharides), but its bonds cannot be broken by human digestive enzymes, so it yields little, ifany, energy. The accompanying table summarises the carbohydrate family of compounds.REVIEW ITThe carbohydrate family SIMPLE CARBOHYDRATES (SUGARS)COMPLEX CARBOHYDRATESMonosaccharides:› Glucose› Fructose› GalactosePolysaccharides:› Glycogen*› Starches› FibresDisaccharides:› Maltose› Sucrose› Lactose *Glycogen is a complex carbohydrate (a polysaccharide) but not a dietary source of carbohydrate.CHAPTER 4 THE CARBOHYDRATES: SUGARS, STARCHES AND DIETARY FIBRE 103Eleanor, Whitney, et al. Understanding Nutrition, Cengage Australia, 2016. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/think/detail.action?docID=5024519.Created from think on 2021-03-22 18:34:59.Copyright © 2016. Cengage Australia. All rights reserved.The ultimate goal of digestion and absorption of sugars and starches is to break theminto small molecules – chiefly glucose – that the body can absorb and use. The largestarch molecules require extensive breakdown; the disaccharides need only be brokenonce and the monosaccharides not at all. The initial splitting begins in the mouth;the final splitting and absorption occur in the small intestine; and conversion to acommon energy currency (glucose) takes place in the liver. The details follow.CARBOHYDRATE DIGESTIONFigure 4.10 traces the digestion of carbohydrates through the GI tract. When a personeats foods containing starch, enzymes hydrolyse the long chains to shorter chains,the short chains to disaccharides and, finally, the disaccharides to monosaccharides.This process begins in the mouth.In the mouthIn the mouth, thoroughly chewing high-fibre foods slows eating and stimulates theflow of saliva. The salivary enzyme amylase starts to work, hydrolysing starch toshorter polysaccharides and to the disaccharide maltose. In fact, you can taste thechange if you hold a piece of starchy food like a dry biscuit in your mouth for a fewminutes without swallowing it – the dry biscuit begins tasting sweeter as the enzymeacts on it. Because food is in the mouth for only a short time, very little carbohydrate digestiontakes place there; it begins again in the small intestine.In the stomachThe swallowed bolus mixes with the stomach’s acid and protein-digesting enzymes, whichinactivate salivary amylase. Thus the role of salivary amylase in starch digestion is relativelyminor. To a small extent, the stomach’s acid continues breaking down starch, but its juicescontain no enzymes to digest carbohydrate. Dietary fibre lingers in the stomach and delaysgastric emptying, thereby providing a feeling of fullness and satiety.In the small intestineThe small intestine performs most of the work of carbohydrate digestion. A major carbohydratedigesting enzyme, pancreatic amylase, enters the intestine via the pancreatic duct and continuesbreaking down the polysaccharides to shorter glucose chains and maltose. The final step takesplace on the outer membranes of the intestinal cells. There, specific enzymes break downspecific disaccharides:• Maltase breaks maltose into two glucose molecules.• Sucrase breaks sucrose into one glucose and one fructose molecule.• Lactase breaks lactose into one glucose and one galactose molecule.At this point, all polysaccharides and disaccharides have been broken down to monosaccharides –mostly glucose molecules, with some fructose and galactose molecules as well.The short chains ofglucose units that resultfrom the breakdownof starch are knownas dextrins. The wordsometimes appears onfood labels becausedextrins can be usedas thickening agents inprocessed foods.Reminder: A bolusis a portion of foodswallowed at one time.Reminder: In general,the word ending -aseidentifies an enzyme,and the beginning ofthe word identifiesthe molecule that theenzyme works on.DIGESTION AND ABSORPTION OF CARBOHYDRATESLEARN ITSummarise carbohydrate digestion and absorption.When a person eats carbohydrate-richfoods, the body receives a valuablecommodity – glucose.Banana Stock104 UNDERSTANDING NUTRITIONEleanor, Whitney, et al. Understanding Nutrition, Cengage Australia, 2016. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/think/detail.action?docID=5024519.Created from think on 2021-03-22 18:34:59.Copyright © 2016. Cengage Australia. All rights reserved.The pancreas produces anamylase that is releasedthrough the pancreatic ductinto the small intestine:StarchSmallpolysaccharides,maltosePancreaticamylaseThen disaccharidase enzymeson the surface of the smallintestinal cells hydrolyse thedisaccharides intomonosaccharides:Fructose+GlucoseSucroseGalactose+GlucoseLactoseMaltase Glucose+GlucoseMaltoseSmall intestine and pancreasSucraseLactaseThe salivary glands secretesaliva into the mouthto moisten the food. Thesalivary enzyme amylasebegins digestion:Starch AmylaseSmallpolysaccharides, maltoseSmall intestineDietary fibre is not digested,and it delays absorption ofother nutrients.Large intestineMost dietary fibre passes intactthrough the digestive tract to thelarge intestine. Here, bacterialenzymes digest dietary fibre:Some dietaryfatty acids,fibregasenzymesShort-chain BacterialDietary fibre holds water;regulates bowel activity; andbinds substances such as bile,cholesterol and some minerals,carrying them out of the body.STARCH DIETARY FIBRESalivary Mouthglands(Liver)(Gall bladder)StomachPancreasSmallintestineLargeintestineMouth and salivary glands MouthThe mechanical action of themouth crushes and tearsdietary fibre in food and mixesit with saliva to moisten it forswallowing.StomachDietary fibre is not digested,and it delays gastric emptying.Intestinal cells absorb thesemonosaccharides.StomachStomach acid inactivatessalivary enzymes, haltingstarch digestion.FIGURE 4.10 Animated! Carbohydrate digestion in the GI tractWatch an animation of thistopic in CourseMate.CHAPTER 4 THE CARBOHYDRATES: SUGARS, STARCHES AND DIETARY FIBRE 105Eleanor, Whitney, et al. Understanding Nutrition, Cengage Australia, 2016. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/think/detail.action?docID=5024519.Created from think on 2021-03-22 18:34:59.Copyright © 2016. Cengage Australia. All rights reserved.In the large intestineWithin one to four hours after a meal, all the sugars and most of the starches have been digested.Only the dietary fibre remains in the digestive tract. Dietary fibre in the large intestine attractswater, which softens the stools for passage without straining. Also, bacteria in the GI tractferment some dietary fibre. This process generates water, gas and short-chain fatty acids(described in Chapter 5).* The colon uses these small fat molecules for energy. Metabolism ofshort-chain fatty acids also occurs in the cells of the liver. Dietary fibre, therefore, can contributesome energy (6 to 10 kilojoules per gram), depending on the extent to which it is broken downby bacteria and the fatty acids are absorbed.CARBOHYDRATE ABSORPTIONGlucose is unique in that it can be absorbed to some extent through the lining of the mouth,but for the most part, nutrient absorption takes place in the small intestine. Glucose andgalactose traverse the cells lining the small intestine by active transport; fructose is absorbed byfacilitated diffusion, which slows its entry and produces a smaller rise in blood glucose. Likewise,unbranched chains of starch are digested slowly and produce a smaller rise in blood glucosethan branched chains, which have many more places for enzymes to attack and release glucoserapidly.As the blood from the intestines circulates through the liver, cells there take up fructoseand galactose and convert them to other compounds, most often to glucose, as shownin Figure 4.11. Thus, all disaccharides provide at least one glucose molecule directly, andthey can provide another one indirectly – through the conversion of fructose and galactoseto glucose.Starches and sugarsare called availablecarbohydrates becausehuman digestiveenzymes break themdown for the body’s use.In contrast, dietary fibreis called unavailablecarbohydrate becausehuman digestive enzymescannot break the bonds.PUTTINGCOMMONSENSE TOTHE TESTThe majority ofcarbohydratedigestion occurs inthe large intestine.FALSE*The short-chain fatty acids produced by GI bacteria are primarily acetic acid, propionic acid and butyric acid.Small intestineMonosaccharides, the end products ofcarbohydrate digestion, enter the capillariesof the intestinal villi.In the liver, galactose andfructose are converted toglucose.GlucoseFructoseMonosaccharides travel to Galactosethe liver via the portal vein.123Key:FIGURE 4.11 Absorption of monosaccharides106 UNDERSTANDING NUTRITIONEleanor, Whitney, et al. Understanding Nutrition, Cengage Australia, 2016. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/think/detail.action?docID=5024519.Created from think on 2021-03-22 18:34:59.Copyright © 2016. Cengage Australia. All rights reserved.LACTOSE INTOLERANCENormally, the intestinal cells produce enough of the enzyme lactase to ensure that thedisaccharide lactose found in milk is both digested and absorbed efficiently. Lactase activity ishighest immediately after birth, as befits an infant whose first and only food for a while will bebreast milk or infant formula. In the great majority of the world’s populations, lactase activitydeclines dramatically during childhood and adolescence to about 5 to 10 per cent of the activityat birth. Only a relatively small percentage (about 30 per cent) of the people in the world retainenough lactase to digest and absorb lactose efficiently throughout adult life.SymptomsWhen more lactose is consumed than the available lactase can handle, lactose molecules remainin the intestine undigested, attracting water and causing bloating, abdominal discomfort anddiarrhoea – the symptoms of lactose intolerance. The undigested lactose becomes food forintestinal bacteria, which multiply and produce irritating acid and gas, further contributing tothe discomfort and diarrhoea.CausesLactase activity commonly declines with age. Lactase deficiency may also develop when theintestinal villi are damaged by disease, certain medicines, prolonged diarrhoea or malnutrition.Depending on the extent of the intestinal damage, lactose malabsorption may be temporary orpermanent. In extremely rare cases, an infant is born with a lactase deficiency.PrevalenceThe prevalence of lactose intolerance varies widely among ethnic groups, indicating thatthe trait is genetically determined. The prevalence of lactose intolerance is lowest amongScandinavians and other northern Europeans and highest among native North Americans andSouth-East Asians.Dietary changesManaging lactose intolerance requires some dietary changes, although total elimination ofmilk products usually is not necessary. Excluding all milk products from the diet can lead tonutrient deficiencies because these foods are a major source of several nutrients, notably themineral calcium, vitamin D and the B vitamin riboflavin. Fortunately, many people with lactoseintolerance can generally consume foods containing up to 6 grams of lactose (½ cup milk)without symptoms. The most successful strategies are to increase the intake of milk productsgradually, take them with other foods in meals and spread their intake throughout the day. Achange in the GI bacteria, not the reappearance of the missing enzyme, accounts for the abilityto adapt to milk products. Importantly, most lactose-intolerant individuals need to manage theirdairy consumption rather than restrict it.2In many cases, lactose-intolerant people can tolerate fermented milk products such asyoghurt. The bacteria in these products digest lactose for their own use, thus reducing thelactose content. Even when the lactose content is equivalent to that of milk, yoghurt producesfewer symptoms. Hard cheeses, such as cheddar, and cottage cheese are often well toleratedEstimated prevalenceof lactose intolerance:• .80% South-EastAsians• 80% Native Americans• 75% AfricanAmericans• 70% AustralianAborigines• 70% Mediterraneanand Middle Easternpeople• 60% Inuit• 50% Hispanics• 20% Caucasians• ,10% NorthernEuropeansIn the digestion and absorption of carbohydrates, the body breaks down starches into the disaccharidemaltose. Maltose and the other disaccharides (lactose and sucrose) from foods are broken down intomonosaccharides. Then monosaccharides are converted mostly to glucose to provide energy for thecells’ work. Dietary fibre helps to regulate the passage of food through the GI system and slows theabsorption of glucose, but dietary fibre contributes little, if any, energy.REVIEW ITCHAPTER 4 THE CARBOHYDRATES: SUGARS, STARCHES AND DIETARY FIBRE 107Eleanor, Whitney, et al. Understanding Nutrition, Cengage Australia, 2016. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/think/detail.action?docID=5024519.Created from think on 2021-03-22 18:34:59.Copyright © 2016. Cengage Australia. All rights reserved.because most of the lactose is removed with the whey during manufacturing. Lactose continuesto diminish as cheese ages.Many lactose-intolerant people use commercially prepared milk products that have beentreated with an enzyme that breaks down the lactose. Alternatively, they take enzyme tabletswith meals or add enzyme drops to their milk. The enzyme hydrolyses much of the lactose inmilk to glucose and galactose, which lactose-intolerant people can absorb without ill effects.Because people’s tolerance to lactose varies widely, lactose-restricted diets must be highlyindividualised. A completely lactose-free diet can be difficult because lactose appears not onlyin milk and milk products but also as an ingredient in many non-dairy foods such as breads,cereals, breakfast drinks, salad dressings and cake mixes. People on strict lactose-free diets needto read labels and avoid foods that include milk, milk solids, whey (milk liquid) and casein (milkprotein, which may contain traces of lactose). They also need to check all medications with thepharmacist because 20 per cent of prescription drugs and 5 per cent of over-the-counter drugscontain lactose as a filler.People who consume few or no milk products must take care to meet riboflavin, vitamin Dand calcium needs. Later chapters on the vitamins and minerals offer help with finding goodnon-milk sources of these nutrients.Lactose in selectedfoods (per 100 g serving):• butter, regular 1 g• cheddar cheese 0.1 g• cottage cheese2.7–3.4 g• ice-cream 4.7–5.9 g• milk (whole) 4.6 g• milk (skim) 5 g• Milo powder 12.7 g• plain or fruit buns0–0.1 g• soy milk 0 g• wholegrain bread 0 g• yoghurt (natural,whole) 4.7 gNote: Yoghurt is oftenenriched with nonfat milk solids, whichincrease its lactosecontent to a level higherthan that of milk.PUTTINGCOMMONSENSE TOTHE TESTPeople who sufferlactose intolerancemust avoid alldairy foods.FALSECURRENT RESEARCH IN NUTRITIONFructose and FODMAPSFODMAPs are found in the foods we eat. The term FODMAP is an acronym forFermentable Oligosaccharides, Disaccharides, Monosaccharides and Polyols. FODMAPsare only considered FODMAPs if people are sensitive to their effects in the digestivetract. Fructose, a monosaccharide, can be a FODMAP (as can the disaccharide lactose).Fructose is commonly found in fruits and although a person needing a low FODMAPdiet may limit their intake of fruit, not all fruits have the same amount of fructose in them.This means, (much like lactose intolerance management), that being on a low FODMAPdiet is about managing exposure to FODMAPs for the individual.Lactose intolerance is a relatively common condition that occurs when there is insufficient lactaseto digest the disaccharide lactose found in milk and milk products. Symptoms generally include GIdistress. Because treatment requires limiting milk intake, other sources of calcium, riboflavin andvitamin D must be included in the diet.REVIEW ITGLUCOSE IN THE BODYLEARN ITExplain how the body maintains its blood glucose concentration and what happens when bloodglucose rises too high or falls too low.The primary role of the available carbohydrates in human nutrition is to supply the body’s cellswith glucose for energy. Starch contributes most to the body’s glucose supply, but as explainedearlier, any of the monosaccharides can also provide glucose.Scientists have long known that the primary role of glucose in the body is to provide energy,but they have only recently uncovered additional roles that glucose and other sugars perform inthe body.3 Sugar molecules dangle from many of the body’s protein and fat molecules, withdramatic consequences. Sugars attached to a protein change the protein’s shape and function;The study of sugars isglycobiology.108 UNDERSTANDING NUTRITIONEleanor, Whitney, et al. Understanding Nutrition, Cengage Australia, 2016. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/think/detail.action?docID=5024519.Created from think on 2021-03-22 18:34:59.Copyright © 2016. Cengage Australia. All rights reserved.when they bind to lipids in a cell’s membranes , sugars alter the way cells recognise eachother.4Cancer cells coated with sugar molecules, for example, are able to sneak by the cells of theimmune system. Scientists are now trying to use sugar molecules to create an anticancer vaccine.Further advances in knowledge are sure to reveal numerous ways these simple, yet remarkablesugar molecules influence the health of the body.A PREVIEW OF CARBOHYDRATE METABOLISMGlucose plays the central role in carbohydrate metabolism. This brief discussion provides justenough information about carbohydrate metabolism to illustrate that the body needs and usesglucose as a chief energy nutrient. Chapter 7 provides a full description of energy metabolism.Storing glucose as glycogenThe liver stores about one-third of the body’s total glycogen and releases glucose into thebloodstream as needed. After a meal, blood glucose rises, and liver cells link the excess glucosemolecules by condensation reactions into long, branching chains of glycogen. When bloodglucose falls, the liver cells break glycogen by hydrolysis reactions into single molecules ofglucose and release them into the bloodstream. Thus, glucose becomes available to supplyenergy to the brain and other tissues regardless of whether the person has eaten recently.Muscle cells can also store glucose as glycogen (the other two-thirds), but they hoard most oftheir supply, using it just for themselves during exercise. The brain maintains a small amountof glycogen, which is thought to provide an emergency energy reserve during times of severeglucose deprivation.5Glycogen holds water and, therefore, is rather bulky. The body can store only enoughglycogen to provide energy for relatively short periods of time – less than a day during restand a few hours at most during exercise. For its long-term energy reserves – for use over daysor weeks of food deprivation – the body uses its abundant, water-free fuel, fat, as Chapter 5describes.Using glucose for energyGlucose fuels the work of most of the body’s cells. Inside a cell, enzymes breakglucose in half. These halves can be put back together to make glucose, or they can befurther broken down into even smaller fragments (never again to be reassembled toform glucose). The small fragments can yield energy when broken down completelyto carbon dioxide and water (see Chapter 7).The liver’s glycogen stores last only for hours, not for days, so to keep providingglucose to meet the body’s energy needs, a person needs to eat dietary carbohydratefrequently. Yet people who do not always attend faithfully to their body’s carbohydrateneeds still survive. How do they manage without glucose from dietary carbohydrate? Dothey simply draw energy from the other two energy-yielding nutrients, fat and protein?The answer is a simple ‘yes’ but the process is far from simple.Making glucose from proteinGlucose is the preferred energy source for brain cells, other nerve cells and developingred blood cells. Body protein can be converted to glucose to some extent, but proteinhas a number of tasks that no other nutrient can do. Body fat cannot be convertedto glucose to any significant extent. Thus, when a person does not replenish depleted glycogenstores by eating carbohydrate, body proteins are broken down to make glucose to fuel thesespecial cells.The conversion of protein to glucose is called gluconeogenesis – literally, the making of newglucose. Only adequate dietary carbohydrate can prevent this use of protein for energy, and thisrole of carbohydrate is known as its protein-sparing action.These combinationmolecules are knownas glycoproteins andglycolipids, respectively.The carbohydrates of grains, vegetables,fruits and legumes supply most of theenergy in a well-balanced diet.Getty/Brian LeatartCHAPTER 4 THE CARBOHYDRATES: SUGARS, STARCHES AND DIETARY FIBRE 109Eleanor, Whitney, et al. Understanding Nutrition, Cengage Australia, 2016. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/think/detail.action?docID=5024519.Created from think on 2021-03-22 18:34:59.Copyright © 2016. Cengage Australia. All rights reserved.Making ketone bodies from fat fragmentsAn inadequate supply of carbohydrate can shift the body’s energy metabolism in a precariousdirection. With less carbohydrate providing glucose to meet the brain’s energy needs, fat takesan alternative metabolic pathway; instead of entering the main energy pathway, fat fragmentscombine with each other, forming ketone bodies. Ketone bodies provide an alternative fuelsource during starvation, but when their production exceeds their use, they accumulate inthe blood, causing ketosis, a condition that disturbs the body’s normal acid–base balance,as Chapter 7 describes. (Highlight 9 explores ketosis and the health consequences of lowcarbohydrate diets further.)To spare body protein and prevent ketosis, the body needs at least 50 to 100 gramsof carbohydrate a day. Dietary recommendations urge people to select abundantly fromcarbohydrate-rich foods to provide for considerably more.Using glucose to make fatAfter meeting its energy needs and filling its glycogen stores to capacity, the body must find away to handle any extra glucose. At first, energy metabolism shifts to use more glucose insteadof fat. If that isn’t enough to restore glucose balance, the liver breaks glucose into smallermolecules and puts them together into the more permanent energy-storage compound –fat. Thus, when carbohydrate is abundant, fat is either conserved or created. The fat thentravels to the fatty tissues of the body for storage. Unlike the liver cells, which can store onlyenough glycogen to meet less than a day’s energy needs, fat cells can store seemingly unlimitedquantities of fat.THE CONSTANCY OF BLOOD GLUCOSEEvery body cell depends on glucose for its fuel to some extent, and the cells of the brain and therest of the nervous system depend almost exclusively on glucose for their energy. The activitiesof these cells never cease, and they have limited ability to store glucose. Day and night, theycontinually draw on the supply of glucose in the fluid surrounding them. To maintain thesupply, a steady stream of blood moves past these cells bringing more glucose from either theintestines (food) or the liver (via glycogen breakdown or gluconeogenesis).Maintaining glucose homeostasisTo function optimally, the body must maintain blood glucose within limits that permit the cellsto nourish themselves. If blood glucose falls below normal, a person may become dizzy andweak; if it rises above normal, a person may become fatigued. Left untreated, fluctuations to theextremes – either high or low – can be fatal.The regulating hormonesBlood glucose homeostasis is regulated primarily by two hormones: insulin, which movesglucose from the blood into the cells, and glucagon, which brings glucose out of storage whennecessary. Figure 4.12 depicts these hormonal regulators at work.After a meal, as blood glucose rises, special cells of the pancreas respond by secreting insulininto the blood.* In general, the amount of insulin secreted corresponds with the rise in glucose.As the circulating insulin contacts the receptors on the body’s other cells, the receptors respondby ushering glucose from the blood into the cells. Most of the cells take only the glucose theycan use for energy right away, but the liver and muscle cells can assemble the small glucose unitsinto long, branching chains of glycogen for storage. The liver cells can also convert glucose to fatNormal blood glucose(fasting): 4 to 6 mmol/L(published values varyslightly).PUTTINGCOMMONSENSE TOTHE TESTGlucose fuels themajority of thebody’s energyneeds.TRUE*The beta cells, one of several types of cells in the pancreas, secrete insulin in response to elevated blood glucose concentration.Reminder:Homeostasis is themaintenance of constantinternal conditions by thebody’s control systems.110 UNDERSTANDING NUTRITIONEleanor, Whitney, et al. Understanding Nutrition, Cengage Australia, 2016. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/think/detail.action?docID=5024519.Created from think on 2021-03-22 18:34:59.Copyright © 2016. Cengage Australia. All rights reserved.for export to other cells. Thus, elevated blood glucose returns to normal levels as excess glucoseis stored as glycogen and fat.When blood glucose falls (as occurs between meals), other special cells of the pancreasrespond by secreting glucagon into the blood.* Glucagon raises blood glucose by signalling theliver to break down its glycogen stores and release glucose into the blood for use by all the otherbody cells.Another hormone that signals the liver cells to release glucose is the ‘fight-or-flight’hormone, adrenaline (or epinephrine). When a person experiences stress, adrenaline actsquickly, ensuring that all the body cells have energy fuel in emergencies. Among its many rolesin the body, adrenaline works to release glucose from liver glycogen to the blood.Balancing within the normal rangeThe maintenance of normal blood glucose ordinarily depends on two processes. When bloodglucose falls below normal, food can replenish it, or in the absence of food, glucagon can signalthe liver to break down glycogen stores. When blood glucose rises above normal, insulin cansignal the cells to take in glucose for energy. Eating balanced meals at regular intervals helps thebody maintain a happy medium between the extremes. Balanced meals that provide abundantcomplex carbohydrates, including dietary fibre and a little fat, help to slow down the digestionand absorption of carbohydrate so that glucose enters the blood gradually, providing a steady,ongoing supply.*The alpha cells of the pancreas secrete glucagon in response to low blood glucose.PancreasGlucagonInsulinLiverIntestineaThe stress hormone epinephrine and otherhormones also bring glucose out of storage.MuscleFat cellInsulin stimulates the uptakeof glucose into cells andstorage as glycogen in theliver and muscles. Insulin alsostimulates the conversionof excess glucose into fatfor storage.3As the body’s cells useglucose, blood levels decline.4 4Low blood glucose stimulatesthe pancreas to release glucagoninto the bloodstream.5 5Glucagon stimulates liver cellsto break down glycogen andrelease glucose into the blood.a6 67 7 Blood glucose begins to rise.GlucoseInsulinGlucagonGlycogenWhen a person eats, bloodglucose rises.11 2 3 3High blood glucose stimulatesthe pancreas to release insulininto the bloodstream.2Key:BloodvesselFIGURE 4.12 Maintaining blood glucose homeostasisCHAPTER 4 THE CARBOHYDRATES: SUGARS, STARCHES AND DIETARY FIBRE 111Eleanor, Whitney, et al. Understanding Nutrition, Cengage Australia, 2016. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/think/detail.action?docID=5024519.Created from think on 2021-03-22 18:34:59.Copyright © 2016. Cengage Australia. All rights reserved.Falling outside the normal rangeThe influence of foods on blood glucose has given rise to the oversimplification that foods governblood glucose concentrations. Foods do not; the body does. In some people, however, bloodglucose regulation fails. When this happens, either of two conditions can result: diabetes orhypoglycaemia. People with these conditions often plan their diets to help maintain their bloodglucose within a normal range.DiabetesIn diabetes, blood glucose surges after a meal and remains above normal levels becauseinsulin is either inadequate or ineffective. Thus, blood glucose is central to diabetes, but dietarycarbohydrates do not cause diabetes.There are two main types of diabetes. In type 1 diabetes, the less common type, the pancreasfails to produce insulin. Although the exact cause is unclear, some research suggests that ingenetically susceptible people, certain viruses activate the immune system to attack and destroycells in the pancreas as if they were foreign cells. In type 2 diabetes, the more common type ofdiabetes, the cells fail to respond to insulin. This condition tends to occur as a consequenceof obesity. As the incidence of obesity in Australia and New Zealand has risen in recent decades,the incidence of diabetes has followed. Latest estimates show that nearly 0.9 million Australianshave diabetes, but up to half of the people with type 2 diabetes remain undiagnosed.6 ForNew Zealand, diabetes rates are two to three times higher in Maori and Pacific populationswhen compared with the entire population.7 This trend is most notable among children andadolescents, as obesity reaches epidemic proportions. Because obesity can precipitate type 2diabetes, the best preventive measure is to maintain a healthy body weight. Sweets and lolliesare not strictly excluded from the diabetic diet as they once were; they can be eaten in limitedamounts with meals, as part of a healthy diet. Chapter 15 describes the type of diabetes thatdevelops in some women during pregnancy (gestational diabetes), and Chapter 18 gives fullcoverage of type 1 and type 2 diabetes and their associated problems.HypoglycaemiaIn healthy people, blood glucose rises after eating and then gradually falls back into the normalrange. The transition occurs without notice. Should blood glucose drop below normal, a personwould experience the symptoms of hypoglycaemia: weakness, rapid heartbeat, sweating, anxiety,hunger and trembling. Most commonly, hypoglycaemia is a consequence of poorly manageddiabetes. Too much insulin, strenuous physical activity, inadequate food intake or illness cancause blood glucose levels to plummet.Hypoglycaemia in healthy people is rare. Most people who experience hypoglycaemianeed only adjust their diets by replacing refined carbohydrates with carbohydrates rich indietary fibre and ensuring an adequate protein intake. In addition, smaller meals eaten morefrequently may help. Hypoglycaemia caused by certain medications, pancreatic tumours,overuse of insulin, alcohol abuse, uncontrolled diabetes or other illnesses requires medicalintervention.The glycaemic responseThe glycaemic response refers to how quickly glucose is absorbed after a person eats, how highblood glucose rises and how quickly it returns to normal. Slow absorption, a modest rise in bloodglucose and a smooth return to normal are desirable (a low glycaemic response). Fast absorption,a surge in blood glucose and an overreaction that plunges glucose below normal are less desirable(a high glycaemic response). Different foods have different effects on blood glucose.The rate of glucose absorption is particularly important to people with diabetes, who maybenefit from limiting foods that produce too great a rise, or too sudden a fall, in blood glucose.To aid their choices, they may be able to use the glycaemic index (GI), a method of classifyingfoods according to their potential to raise blood glucose.Blood glucose(fasting):• prediabetes: 6.1 to7 mmol/L• diabetes: greater than7 mmol/L on two ormore tests performedon different daysThe condition ofhaving blood glucoselevels higher thannormal, but below thediagnosis of diabetes,is sometimes calledprediabetes.A related term,glycaemic load, reflectsboth the glycaemicindex and the amount ofcarbohydrate.112 UNDERSTANDING NUTRITIONEleanor, Whitney, et al. Understanding Nutrition, Cengage Australia, 2016. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/think/detail.action?docID=5024519.Created from think on 2021-03-22 18:34:59.Copyright © 2016. Cengage Australia. All rights reserved.Figure 4.13 ranks selected foods by their GI.8 Some studies have shown that selecting foodswith a low GI is a practical way to improve glucose control.9Lowering the glycaemic index of the diet may improve blood lipids and reduce the risk of heartdisease as well.10 A low glycaemic index diet may also help with weight management, althoughresearch findings are mixed.11 Dietary fibre and other slowly digested carbohydrates prolongthe presence of foods in the digestive tract, thus providing greater satiety and diminishing theinsulin response, which can help with weight control.12 In contrast, the rapid absorption ofglucose from a high glycaemic diet seems to increase the risk of heart disease and promoteovereating in some overweight people.13Despite these possible benefits, the usefulness of the glycaemic index is still being debated.Those opposing the use of the glycaemic index argue that it is not sufficiently supported byscientific research. The glycaemic index has been determined for relatively few foods, and whenthe glycaemic index has been established, it is based on an average of multiple tests with widevariations in their results. Values vary because of differences in the physical and chemicalcharacteristics of foods, testing methods of laboratories and digestive processes of individuals.PeanutsSoybeansCashews, cherriesBarleyMilk, kidney beans, chickpeasButter beansYoghurtTomato juice, navy beans, apples, pearsApple juiceBran cereals, black-eyed peas, peachesChocolate, puddingGrapesMacaroni, carrots, green peas, baked beansRye bread, orange juiceBananaWheat bread, corn, pound cakeBrown riceCola, pineappleIce-creamRaisins, white riceCouscousWatermelon, popcorn, bagelPumpkin, doughnutSports drinks, jelly beansCornflakesBaked potatoWhite breadLOW HIGHFIGURE 4.13 Glycaemic index of selected foodsAPPLICATIONS OF NUTRITIONAL RESEARCHDiabetes and glycaemic indexPeople with type 2 diabetes remain concerned about the role that carbohydrates havein regulating their blood glucose levels. Dietary advice is considered the most importantlifestyle message that can positively affect blood glucose control. In recent years, thefocus on the nutritional therapy for type 2 diabetes has changed from focusing on theamount of carbohydrates to include the importance of low glycaemic index foods toreduce the rise in blood glucose after a meal. Clinical research is demonstrating thatlow GI diets (and regular moderate exercise) can assist with the management of not onlyblood glucose, but also blood lipids in people with type 2 diabetes.Furthermore, the practical utility of the glycaemic index is limited because this information isneither provided on food labels nor intuitively apparent. Indeed, a food’s glycaemic index is notalways what one might expect. Ice-cream, for example, is a high-sugar food but produces less ofa glycaemic response than baked potatoes, a high-starch food. This effect is most likely becausethe fat in the ice-cream slows gastrointestinal motility and thus the rate of glucose absorption.Mashed potatoes produce more of a response than honey, probably because the fructose contentCHAPTER 4 THE CARBOHYDRATES: SUGARS, STARCHES AND DIETARY FIBRE 113Eleanor, Whitney, et al. Understanding Nutrition, Cengage Australia, 2016. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/think/detail.action?docID=5024519.Created from think on 2021-03-22 18:34:59.Copyright © 2016. Cengage Australia. All rights reserved.of honey has little effect on blood glucose. In fact, sugars such as fructose generally have amoderate to low glycaemic index and can have a positive effect on glycaemic control.14 Perhapsmost relevant to real life, a food’s glycaemic effect differs depending on plant variety, foodprocessing, cooking method and whether it is eaten alone or with other foods.15 Most peopleeat a variety of foods, cooked and raw, that provide different amounts of carbohydrate, fat andprotein – all of which influence the glycaemic index of a meal.Paying attention to the glycaemic index may not be necessary because current guidelinesalready suggest many low glycaemic index choices: whole grains, legumes, vegetables, fruitsand dairy products. In addition, eating frequent, small meals spreads glucose absorption acrossthe day and thus offers similar metabolic advantages to eating foods with a low glycaemicresponse. People wanting to follow a low glycaemic diet should be careful not to adopt a lowcarbohydrate diet as well. The problems associated with a low carbohydrate diet are addressedin Highlight 9.Dietary carbohydrates provide glucose that can be used by the cells for energy stored by the liver andmuscles as glycogen, or converted into fat if intakes exceed needs. All of the body’s cells depend onglucose; those of the central nervous system are especially dependent on it. Without glucose, the bodyis forced to break down its protein tissues to make glucose and to alter energy metabolism to makeketone bodies from fats. Blood glucose regulation depends primarily on two pancreatic hormones:insulin to move glucose from the blood into the cells when levels are high, and glucagon to freeglucose from glycogen stores and release it into the blood when levels are low. The glycaemic indexmeasures how blood glucose responds to foods.REVIEW ITHEALTH EFFECTS AND RECOMMENDEDINTAKES OF SUGARSLEARN ITDescribe how added sugars can contribute to health problems.Ever since people first discovered honey and dates, they have enjoyed the sweetness of sugars.In Australia and New Zealand, the natural sugars of milk, fruits, vegetables and grains accountfor about half of the sugar intake; the other half consists of sugars that have been refined andadded to foods for a variety of purposes. The use of added sugars has risen steadily over thepast several decades, in Australia and New Zealand and around the world, with soft drinks andsugared fruit drinks accounting for most of the increase.16 These added sugars assume variousnames on food labels: sucrose, invert sugar, corn sugar, corn syrups and solids, high-fructosecorn syrup and honey. A food is likely to be high in added sugars if its ingredient list starts withany of the sugars named in Table 4.1 or if it includes several of them.HEALTH EFFECTS OF SUGARSIn moderate amounts, sugars add pleasure to meals without harming health. In excess, however,they can be detrimental in two ways: sugars can contribute to nutrient deficiencies by supplyingenergy (kilojoules) without providing nutrients; sugars contribute to tooth decay.Nutrient deficienciesFoods that contain large amounts of added sugar, such as cakes, lollies (candies) and soft drinks,deliver glucose and energy with few, if any, other nutrients. By comparison, foods such as wholegrains, vegetables, legumes and fruits that contain some natural sugars and lots of starchesAs an additive, sugar:• enhances flavour• supplies texture andcolour to baked goods• provides fuel forfermentation, causingbread to rise orproducing alcohol• acts as a bulkingagent in ice-creamand baked goods• acts as a preservativein jams• balances the acidity oftomato- and vinegarbased products.114 UNDERSTANDING NUTRITIONEleanor, Whitney, et al. Understanding Nutrition, Cengage Australia, 2016. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/think/detail.action?docID=5024519.Created from think on 2021-03-22 18:34:59.Copyright © 2016. Cengage Australia. All rights reserved.and dietary fibre deliver protein, vitamins and minerals along withtheir glucose and energy.A person spending 800 kilojoules of a day’s energy allowance ona 650-mL soft drink gets little of value for those energy ‘dollars’. Incontrast, a person using 800 kilojoules on three slices of wholegrainbread gets at least 9 grams of protein, 6 grams of fibre, plus severalof the B vitamins with those kilojoules. For the person who wantssomething sweet, a reasonable compromise might be two slices ofbread with a teaspoon of jam on each. The amount of sugar a personcan afford to eat depends on how many kilojoules are available beyondthose needed to deliver indispensable vitamins and minerals.Some people believe that because honey is a natural food, itis nutritious – or, at least, more nutritious than sugar.* A look attheir chemical structures reveals the truth. Honey, like table sugar,contains glucose and fructose. The primary difference is that intable sugar, the two monosaccharides are bonded together as adisaccharide, whereas in honey some of them are free. Whether aperson eats monosaccharides individually, as in honey, or linked together, as in table sugar, theyend up the same way in the body: as glucose and fructose.Honey does contain a few vitamins and minerals, but not many. Honey is denser thancrystalline sugar, too, so it provides more energy per spoonful.This is not to say that all sugar sources are alike, for some are more nutritious than others.Consider a fruit, such as an orange. The fruit may give you the same amounts of fructose andglucose and the same amount of energy as a spoonful of sugar or honey, but the packaging is*Honey should never be fed to infants because of the risk of botulism. Chapters 16 and 19 provide more details.TABLE 4.1 Examples of added sugars brown sugar: refined white sugar crystals to which manufacturers have added molasses syrup with natural flavour andcolour; 91 to 96 per cent pure sucrosecorn sweeteners: corn syrup and sugars derived from corncorn syrup: a syrup made from cornstarch (cornflour) that has been treated with acid, high temperatures and enzymesthat produce glucose, maltose and dextrins. See also high-fructose corn syrup (HFCS)dextrose: an older name for glucosegranulated sugar: crystalline sucrose; 99.9 per cent purehigh-fructose corn syrup (HFCS): a syrup made from cornstarch that has been treated with an enzyme that convertssome of the glucose to the sweeter fructose; made especially for use in processed foods and beverages, where it is thepredominant sweetener. With a chemical structure similar to sucrose, HFCS has a fructose content of 42, 55 or 90 percent, with glucose making up the remainderhoney: sugar (mostly sucrose) formed from nectar gathered by bees. An enzyme splits the sucrose into glucose andfructose. Composition and flavour vary, but honey always contains a mixture of sucrose, fructose and glucoseicing sugar: finely powdered sucrose, 99.9 per cent purelevulose: an older name for fructosemolasses: the thick brown syrup produced during sugar refining. Molasses retains residual sugar and other by-productsand a few minerals; blackstrap molasses contains significant amounts of calcium and ironraw sugar: partially refined crystals harvested during sugar processingwhite sugar: pure sucrose or ‘table sugar’, produced by dissolving, concentrating and recrystallising raw sugar Over half of the added sugars in our diet come from soft drinksand table sugar; however, baked goods, fruit drinks, ice-cream,lollies and breakfast cereals also make substantial contributions.Shutterstock.com/Kamil MacniakCHAPTER 4 THE CARBOHYDRATES: SUGARS, STARCHES AND DIETARY FIBRE 115Eleanor, Whitney, et al. Understanding Nutrition, Cengage Australia, 2016. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/think/detail.action?docID=5024519.Created from think on 2021-03-22 18:34:59.Copyright © 2016. Cengage Australia. All rights reserved.more valuable nutritionally. The sugars in fruit arrive in the body diluted ina large volume of water, packaged in dietary fibre and mixed with essentialvitamins, minerals and phytochemicals.As these comparisons illustrate, the significant difference between sugarsources is not between ‘natural’ honey and ‘purified’ sugar but betweenconcentrated sweets and the diluted, naturally occurring sugars that sweetenfoods. You can suspect an exaggerated nutrition claim when someone assertsthat one product is more nutritious than another because it contains honey.Sugar can contribute to nutrient deficiencies only by displacing nutrients.For nutrition’s sake, the appropriate attitude to take is not that sugar is ‘bad’and must be avoided, but that nutritious foods must come first. If nutritiousfoods crowd sugar out of the diet, that is fine – but not the other way around.As always, the goals to seek are balance, variety and moderation.Dental cariesSugars from foods and from the breakdown of starches in the mouth cancontribute to tooth decay. Bacteria in the mouth ferment the sugars and,in the process, produce an acid that erodes tooth enamel (see Figure 4.14),causing dental caries, or tooth decay. People can eat sugar without thishappening, though, for much depends on how long foods stay in the mouth.Sticky foods stay on the teeth longer and continue to yield acid longer thanfoods that are readily cleared from the mouth. For that reason, sugar in a juiceconsumed quickly, for example, is less likely to cause dental caries than sugarin a pastry. By the same token, the sugar in sticky foods such as dried fruitscan be more detrimental than its quantity alone would suggest.Another concern is how often people eat sugar. The bacteria in the mouth produce acid for20 to 30 minutes after each exposure to sugar. If a person eats three lollies at one time, the teethwill be exposed to approximately 30 minutes of acid destruction. But if the person eats threepieces at half-hour intervals, the time of exposure increases to 90 minutes. Likewise, slowlysipping a sugary sports beverage may be more harmful than drinking quickly and clearing themouth of sugar. Non-sugary foods can help remove sugar from tooth surfaces; hence, it is betterto eat sugar with meals than between meals.17 Foods such as milk and cheese may be particularlyhelpful in minimising the effects of the acids and in restoring the lost enamel.Beverages such as soft drinks, orange juice and sports drinks not only contain sugar but alsohave a low pH. These acidic drinks can erode tooth enamel and may explain why dental erosionis highly prevalent today.The development of caries depends on several factors: the bacteria that reside in dentalplaque, the saliva that cleanses the mouth, the minerals that form the teeth and the foods thatremain after swallowing. For most people, good oral hygiene will prevent dental caries. In fact,regular brushing (twice a day, with a fluoride-containing toothpaste) and flossing may be moreeffective in preventing dental caries than restricting sugary foods.RECOMMENDED INTAKES OF SUGARSBecause added sugars deliver energy but few or no nutrients, the National Health and MedicalResearch Council’s 2013 Australian Dietary Guidelines urge consumers to ‘limit intake of foodsand drinks containing added sugars’. Most people need to limit their use of added sugars.Estimates indicate that, on average, each person in Australia consumes about 42 kg of sugar overa year, most as added cane sugar.18To prevent dental caries:• limit between-mealsnacks containingsugars and starches• brush and floss teethregularly• if brushing andflossing are notpossible, at least rinsewith water.AUSTRALIANDIETARYGUIDELINES(2013)Limit intake offoods and drinkscontaining addedsugars, such asconfectionery, sugarsweetened softdrinks and cordials,fruit drinks, vitaminwaters and energyand sports drinks.NerveBlood vesselGumCrownRootcanalBoneDentinEnamelPulp(bloodvessels,nerves)CariesFIGURE 4.14 Dental cariesDental caries begin when acid dissolves theenamel that covers the tooth. If not repaired, thedecay may penetrate the dentine and spreadinto the pulp of the tooth, causing inflammation,abscess and possible loss of the tooth.116 UNDERSTANDING NUTRITIONEleanor, Whitney, et al. Understanding Nutrition, Cengage Australia, 2016. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/think/detail.action?docID=5024519.Created from think on 2021-03-22 18:34:59.Copyright © 2016. Cengage Australia. All rights reserved.ALTERNATIVE SWEETENERSREDUCE THE INTAKE OF ADDED SUGARSThere are many ways to reduce the intake of added sugars.› Use less table sugar when preparing meals and at the table. ›Drink fewer regular soft drinks, sports drinks, energy drinks, 100 per cent fruit juice andfruit drinks; choose water, low-fat milk, or unsweetened tea or coffee instead. If you do drinksugar sweetened beverages, have a small portion.Select fruit for dessert. Eat less cake, biscuits, ice-cream, other desserts, and lollies. If youdo eat these foods, have a small portion.The ingredients list also helps to identify foods with added sugars. A food is likely to be high›› in added sugars if its ingredient list starts with any of the sugars named in Table 4.1. or if itincludes several of them.How many kilojoules from sugar does your favourite beverage or snack provide?HOW TO:Try an interactiveversion of this ‘Howto’ on CourseMate.Sugars pose no major health threat except for an increased risk of dental caries. Excessive intakes,however, may displace needed nutrients and dietary fibre and may contribute to obesity when energyintake exceeds needs. A person deciding to limit daily sugar intake should recognise that not all sugarsneed to be restricted, just concentrated sweets, which are relatively empty of other nutrients and highin energy. Sugars that occur naturally in fruits, vegetables and milk are acceptable.REVIEW IT LEARN ITIdentify the three common types of alternative sweeteners and their chemical properties.In an attempt to control weight gain, blood glucose and dental caries, many consumers turn toalternative sweeteners to help them limit kilojoules and minimise sugar intake. In doing so, theyencounter three sets of alternative sweeteners: artificial sweeteners, herbal products and sugaralcohols. Table 4.2 provides general details about each of the sweeteners.TABLE 4.2 Alternative sweeteners SWEETENER(ADDITIVENUMBER)CHEMICALCOMPOSITIONBODY’SRESPONSERELATIVESWEETNESSaENERGY(kJ/g)ACCEPTABLE DAILYINTAKE (ADI) (mg/kg BODY WEIGHT)bAPPROVALSTATUSArtificial sweetenersAcesulfamepotassium orAcesulfameKc (950)Potassium saltNot digestedor absorbed200015 mg/kg bodyweightd (30 cansdiet soft drink)Approvedfor use inAustralia andNew ZealandAspartamee(951)Amino acids(phenylalanineand asparticacid) and amethyl groupDigested andabsorbed20016 f40 mg/kg bodyweight (18 cansdiet soft drink)gApprovedfor use inAustralia andNew Zealand;warning forPKU CHAPTER 4 THE CARBOHYDRATES: SUGARS, STARCHES AND DIETARY FIBRE 117Eleanor, Whitney, et al. Understanding Nutrition, Cengage Australia, 2016. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/think/detail.action?docID=5024519.Created from think on 2021-03-22 18:34:59.Copyright © 2016. Cengage Australia. All rights reserved. SWEETENER(ADDITIVENUMBER)CHEMICALCOMPOSITIONBODY’SRESPONSERELATIVESWEETNESSaENERGY(kJ/g)ACCEPTABLE DAILYINTAKE (ADI) (mg/kg BODY WEIGHT)bAPPROVALSTATUSCyclamate(952)Sodium orcalcium salt ofcyclamic acidIncompletelyabsorbed;absorbedcyclamateis excretedunchanged;unabsorbedcyclamatemay bemetabolisedby bacteria inthe GI tract30011 mg/kg bodyweight (8 cans ofdiet soft drink)Approvedfor use inAustralia andNew ZealandNeotameAspartame withan additionalside groupattachedNot digestedor absorbed8000018 mg/dayApprovedfor use inAustralia andNew Zealand;no warning forPKUSaccharinh(954)BenzoicsulfimideRapidlyabsorbedand excreted45005 mg/kg bodyweight (10 packetsof sweetener)Approvedfor use inAustralia andNew Zealand;restricted useas a tabletopsweetener inCanadaSucralosei(955)Sucrose withchloride (Cl)atoms instead ofOH groupsNot digestedor absorbed60005 mg/kg bodyweight (6 cans dietsoft drink)Approvedfor use inAustralia andNew ZealandTagatosej(no additivenumber)Monosaccharidesimilar instructureto fructose;naturallyoccurring orderived fromlactoseMostly notabsorbed;someshort-chainfatty acidsabsorbed0.81.57.5 g/dayGRASkapproved;advice toavoid iffructosemalabsorptiveHerbal sweetenersStevial (960)Glycosidesfound in theleaves ofthe SteviarebaudianaherbDigested andabsorbed30004 mg/kg bodyweightApprovedfor use inAustralia andNew Zealand TABLE 4.2118 UNDERSTANDING NUTRITIONEleanor, Whitney, et al. Understanding Nutrition, Cengage Australia, 2016. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/think/detail.action?docID=5024519.Created from think on 2021-03-22 18:34:59.Copyright © 2016. Cengage Australia. All rights reserved. SWEETENER(ADDITIVENUMBER)CHEMICALCOMPOSITIONBODY’SRESPONSERELATIVESWEETNESSaENERGY(kJ/g)ACCEPTABLE DAILYINTAKE (ADI) (mg/kg BODY WEIGHT)bAPPROVALSTATUSSugar alcoholsErythritol(968)Sugar alcoholPartiallyabsorbed insmall intestine;unabsorbedsugar alcoholsmay bemetabolised bybacteria in theGI tract0.70.2– mApprovedfor use inAustralia andNew ZealandIsomalt (953)Sugar alcoholPartiallyabsorbed insmall intestine;unabsorbedsugar alcoholsmay bemetabolised bybacteria in theGI tract0.58.0– mFSANZapprovedLactitol (966)Sugar alcoholPartiallyabsorbed insmall intestine;unabsorbedsugar alcoholsmay bemetabolised bybacteria in theGI tract0.48.0– mFSANZapprovedMaltitol (965)Sugar alcoholPartiallyabsorbed insmall intestine;unabsorbedsugar alcoholsmay bemetabolised bybacteria in theGI tract0.98.5– mFSANZapprovedMannitol(421)Sugar alcoholPartiallyabsorbed insmall intestine;unabsorbedsugar alcoholsmay bemetabolised bybacteria in theGI tract0.76.7– mFSANZapproved TABLE 4.2CHAPTER 4 THE CARBOHYDRATES: SUGARS, STARCHES AND DIETARY FIBRE 119Eleanor, Whitney, et al. Understanding Nutrition, Cengage Australia, 2016. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/think/detail.action?docID=5024519.Created from think on 2021-03-22 18:34:59.Copyright © 2016. Cengage Australia. All rights reserved. SWEETENER(ADDITIVENUMBER)CHEMICALCOMPOSITIONBODY’SRESPONSERELATIVESWEETNESSaENERGY(kJ/g)ACCEPTABLE DAILYINTAKE (ADI) (mg/kg BODY WEIGHT)bAPPROVALSTATUSSorbitol(420)Sugar alcoholPartiallyabsorbed insmall intestine;unabsorbedsugar alcoholsmay bemetabolised bybacteria in theGI tract0.511– mFSANZapprovedXylitol (967)Sugar alcoholPartiallyabsorbed insmall intestine;unabsorbedsugar alcoholsmay bemetabolised bybacteria in theGI tract1.010– mFSANZapproved PKU 5 phenylketonuria; GRAS 5 Generally recognised as safea Relative sweetness is determined by comparing the approximate sweetness of a sugar substitute with the sweetness of pure sucrose, whichhas been defined as 1.0. Chemical structure, temperature, acidity and other flavours of the foods in which the substance occurs all influencerelative sweetness.b Based on a person weighing 70 kg.c Marketed under the trade names Sunett, Sweet One.d Recommendations from the World Health Organization limit acesulfame-K intake to 9 mg per kilogram of body weight per day.e Marketed under the trade names NutraSweet, Equal.f Aspartame provides 16 kilojoules per gram, as does protein, but because so little is used, its energy contribution is negligible. In powderedform, it is sometimes mixed with lactose, however, so a 1 g packet may provide 16 kJ.g Recommendations from the World Health Organization and in Europe and Canada limit aspartame intake to 40 mg per kilogram of bodyweight per day.h Marketed under the trade names Sweet’N Low.i Marketed under the trade names Splenda.j Marketed under the trade names Nutralose, Nutrilatose.k GRAS 5 food additives that are generally recognised as safe. First established by the FDA in 1958, the GRAS list is subject to revision asnew facts become known.l Marketed under the trade names Sweetleaf, Purevia, Truvia, Honey Leaf.m An ADI is ‘not specified’ for sugar alcohols, indicating the highest safety category. They require a warning label, however, that states‘Excess consumption may have a laxative effect’ if reasonable consumption could result in the daily ingestion of 50 g of a sugar alcohol.ARTIFICIAL SWEETENERSArtificial sweeteners are sometimes called non-nutritive sweeteners because they providevirtually no energy. Table 4.2 provides general details about each of the sweeteners. Chapter 9includes a discussion of their use in weight control, and Chapter 19 focuses on some of thesafety issues surrounding their use. Considering that all substances are toxic at some dose, itis little surprise that large doses of artificial sweeteners (or their components or metabolic byproducts) may have adverse effects. The question to ask is whether their ingestion is safe forhuman beings in quantities people normally use (and potentially abuse).TABLE 4.2120 UNDERSTANDING NUTRITIONEleanor, Whitney, et al. Understanding Nutrition, Cengage Australia, 2016. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/think/detail.action?docID=5024519.Created from think on 2021-03-22 18:34:59.Copyright © 2016. Cengage Australia. All rights reserved.STEVIA – A HERBAL PRODUCTThe herb stevia derives from a plant whose leaves have long been used by the people of SouthAmerica to sweeten their beverages. Until recently, stevia was sold in Australia and New Zealandonly as a dietary supplement. In 2008, the Australian and New Zealand Food Authority (FSANZ)approved stevia as an ingredient in foods and beverages.The estimated amount of a sweetener that individuals can safely consume each day over thecourse of a lifetime without adverse effect is known as the Acceptable Daily Intake (ADI).SUGAR ALCOHOLSSome ‘sugar-free’ or reduced-kilojoule products contain sugar alcohols. The sugar alcohols (orpolyols) provide bulk and sweetness in biscuits, hard candies, sugarless gums, jams and jellies.These products claim to be ‘sugar-free’ on their labels, but in this case, ‘sugar-free does notmean free of kilojoules. Sugar alcohols do provide kilojoules, but fewer than their carbohydratecousins, the sugars. Because sugar alcohols yield energy, they are sometimes referred to asnutritive sweeteners. Table 4.2 includes their energy values. Sugar alcohols occur naturally infruits and vegetables; manufacturers also use sugar alcohols in many processed foods to addbulk and texture, to provide a cooling effect or taste, to inhibit browning from heat and to retainmoisture.Sugar alcohols evoke a low glycaemic response. The body absorbs sugar alcohols slowly;consequently, they are slower to enter the bloodstream than other sugars. Common side effectsinclude intestinal gas, abdominal discomfort and diarrhoea. For this reason, regulations requirefood labels to state ‘Excess consumption may have a laxative effect’ if reasonable consumptionof that food could result in the daily ingestion of 50 grams of a sugar alcohol.The real benefit of using sugar alcohols is that they do not contribute to dental caries.Bacteria in the mouth cannot metabolise sugar alcohols as rapidly as sugar. Sugar alcoholsare therefore valuable in chewing gums, breath mints and other products that people keep intheir mouths for a while. Figure 4.15 presents labelling information for products using sugaralternatives. Total Fat 0 g 0%Sodium 0 mg 0%1%Total Carb. 2 gProtein 0 gSugar Alcohol 2 gSugars 0 g *Percent Daily Values (DV) arebased on a 2000 calorie diet.Serving Size 2 pieces (3 g)Servings 6Calories 535% FEWER CALORIES THAN SUGARED GUM.INGREDIENTS: SORBITOL, MALTITOL, GUM BASE, MANNITOL, ARTIFICIAL AND NATURAL FLAVORING, ACACIA,SOFTENERS, TITANIUM DIOXIDE (COLOR), ASPARTAME, ACESULFAME POTASSIUM AND CANDELILLA WAX.PHENYLKETONURICS: CONTAINS PHENYLALANINE.Amount per serving % DV*Not a significant sourceof other nutrients.NutritionFactsThis ingredient listincludes both sugaralcohols and artificialsweetenters.Products that claim to be‘reduced kcalories’ mustprovide at least 25%fewer kcalories per servingthan the comparison item.Products containingless than 0.5 g ofsugar per serving canclaim to be ‘sugarless’or ‘sugar-free’.Products containingaspartame must carrya warning for peoplewith phenylketonuria.FIGURE 4.15 Sugar alternatives on food labelsDLibrary/The Wrigley Co Pty LtdCHAPTER 4 THE CARBOHYDRATES: SUGARS, STARCHES AND DIETARY FIBRE 121Eleanor, Whitney, et al. Understanding Nutrition, Cengage Australia, 2016. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/think/detail.action?docID=5024519.Created from think on 2021-03-22 18:34:59.Copyright © 2016. Cengage Australia. All rights reserved.For consumers choosing to use alternative sweeteners, the Australian Diabetes Counciladvises artificial sweeteners can add variety and enjoyment to a low fat and high fibre eatingplan although they are not a necessity.19 When used in moderation, these sweeteners will dono harm. In fact, they may even help, by providing an alternative to sugar for people withdiabetes, by inhibiting caries-causing bacteria and by limiting energy intake. People may find itappropriate to use any of the sweeteners at times: artificial sweeteners, herbal products, sugaralcohols and sugar itself.Alternative sweeteners provide very few kilojoules, which make them a popular choice by consumersto use in place of sugar. The three main sets of alternative sweeteners are artificial sweeteners, herbalproducts and sugar alcohols. Alternative sweeteners can play a small role in controlling weight anddiabetes and are considered safe to use.REVIEW ITHEALTH EFFECTS AND RECOMMENDED INTAKESOF STARCH AND DIETARY FIBREFoods rich in starch and dietary fibre offer manyhealth benefits.Getty Images/The Image Bank/Rita MassLEARN ITIdentify the health benefits of, and recommendations for, starches and fibres.Carbohydrates and fats are the two major sources of energy in the diet.When one is high, the other is usually low – and vice versa. A diet thatprovides abundant carbohydrate (45 to 65 per cent of energy intake) andsome fat (20 to 35 per cent of energy intake) within a reasonable energyallowance best supports good health. To increase carbohydrate in the diet,focus on whole grains, vegetables, legumes and fruits – foods noted fortheir starch, dietary fibre and naturally occurring sugars.HEALTH EFFECTS OF STARCH AND DIETARY FIBREIn addition to starch, dietary fibre and natural sugars, whole grains,vegetables, legumes and fruits supply valuable vitamins and minerals,with little or no fat. The following paragraphs describe some of the healthbenefits of diets that include a variety of these foods daily.Heart diseaseHigh-carbohydrate diets, especially those rich in whole grains, may protectagainst heart disease and stroke, although sorting out the exact reasonswhy can be difficult.20 Such diets are low in animal fat and cholesterol andhigh in dietary fibre, vegetable proteins and phytochemicals – all factorsassociated with a lower risk of heart disease. (The role of animal fat andcholesterol in heart disease is discussed in Chapter 5. The role of vegetableproteins in heart disease is presented in Chapter 6. The benefits of phytochemicals in diseaseprevention are featured in Highlight 13.)Foods rich in soluble dietary fibre (such as oat bran, barley and legumes) lower bloodcholesterol by binding with bile acids and thereby increasing their excretion. Consequently,the liver must use its cholesterol to make new bile acids. In addition, the bacterial by-productsof dietary fibre fermentation in the colon also inhibit cholesterol synthesis in the liver. The netresult is lower blood cholesterol.Consuming 5 to 10 gof soluble dietary fibredaily reduces bloodcholesterol by 3 to 5%.For perspective, ½ cupdry rolled oats provides8 g of dietary fibre, and½ cup cooked legumesprovides about 6 g ofdietary fibre.122 UNDERSTANDING NUTRITIONEleanor, Whitney, et al. Understanding Nutrition, Cengage Australia, 2016. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/think/detail.action?docID=5024519.Created from think on 2021-03-22 18:34:59.Copyright © 2016. Cengage Australia. All rights reserved.Several researchers have speculated that dietary fibre may also exert its effect by displacingfats in the diet. Whereas this is certainly helpful, even when dietary fat is low, high intakes ofdietary fibre exert a separate and significant cholesterol-lowering effect. In other words, a highdietary fibre diet helps to decrease the risk of heart disease independent of fat intake.20DiabetesHigh-fibre foods – especially whole grains – play a key role in reducing the risk of type 2 diabetes.21When soluble dietary fibre traps nutrients and delays their transit through the GI tract, glucoseabsorption is slowed, which helps to prevent the glucose surge and rebound that seem to beassociated with diabetes onset.Gastrointestinal healthDietary fibre enhances the health of the large intestine. The healthier the intestinal walls, thebetter they can block absorption of unwanted constituents. Fibre such as cellulose (as in cerealbrans, fruits and vegetables) increases stool weight, easing passage and reducing transit time. Inthis way, dietary fibre helps to alleviate or prevent constipation.Taken with ample fluids, dietary fibre can help to prevent several GI disorders. Large, softstools ease elimination for the rectal muscles and reduce the pressure in the lower bowel, makingit less likely that rectal veins will swell (haemorrhoids). Dietary fibre prevents compaction of theintestinal contents, which could obstruct the appendix and permit bacteria to invade and infectit (appendicitis). In addition, dietary fibre stimulates the GI tract muscles so that they retaintheir strength and resist bulging out into pouches known as diverticula (illustrated in Figure H3.2on page 91).22CancerMany, but not all, research studies suggest that increasing dietary fibre protects against coloncancer.23 When the EPIC study of diet and cancer examined the diets of over a half millionpeople in 10 countries for four and a half years, the researchers found an inverse associationbetween dietary fibre and colon cancer.24 People who ate the most dietary fibre (35 grams perday) reduced their risk of colon cancer by 40 per cent compared with those who ate the leastfibre (15 grams per day). Importantly, the study focused on dietary fibre, not fibre supplementsor additives, which lack valuable nutrients and phytochemicals that also help protect againstcancer. Plant foods – vegetables, fruits and wholegrain products – reduce the risks of colon andrectal cancers.25Dietary fibre may help prevent colon cancer by diluting, binding and rapidly removingpotential cancer-causing agents from the colon. In addition, soluble dietary fibre stimulatesbacterial fermentation, a process that produces short-chain fatty acids that lower the pH of thecolon. These small fat molecules activate cancer-killing enzymes and inhibit inflammation inthe colon.26Weight managementHigh-fibre and wholegrain foods help a person to maintain a healthy body weight. Foods richin complex carbohydrates tend to be low in fat and added sugars and can therefore promoteweight loss by delivering less energy per bite. In addition, as dietary fibre absorbs water fromthe digestive juices, it swells, creating feelings of fullness and delaying hunger.Many weight-loss products on the market today contain bulk-inducing dietary fibre such asmethylcellulose, but buying purified fibre compounds like this is neither necessary nor advisable.Most experts agree that the health- and weight-management benefits attributed to dietary fibremay come from other constituents of fibre-containing foods, and not from dietary fibre alone.27For this reason, consumers should select whole grains, legumes, fruits and vegetables instead offibre-rich supplements. High-fibre foods not only add bulk to the diet but are economical andnutritious as well. Table 4.3 summarises dietary fibre and its health benefits.Reminder:• carbohydrate: 17 kJ/g• fat: 37 kJ/gCHAPTER 4 THE CARBOHYDRATES: SUGARS, STARCHES AND DIETARY FIBRE 123Eleanor, Whitney, et al. Understanding Nutrition, Cengage Australia, 2016. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/think/detail.action?docID=5024519.Created from think on 2021-03-22 18:34:59.Copyright © 2016. Cengage Australia. All rights reserved.TABLE 4.3 Dietary fibre: Its characteristics, food sources and health effects in the body FIBRE CHARACTERISTICSMAJOR FOOD SOURCESACTIONS IN THE BODYHEALTH BENEFITSSoluble, viscous, morefermentable› Gums and mucilages› Pectins› Psylliuma› Some hemicellulosesWholegrain products(barley, oats, oat bran,rye), fruits (apples, citrus),legumes, seeds and husks,vegetables; also extractedand used as food additives› Lower blood cholesterolby binding bile› Slow glucose absorption› Slow transit of foodthrough upper GI tract› Hold moisture in stools,softening them› Yield small fat moleculesafter fermentation that thecolon can use for energy› Lower risk of heartdisease› Lower risk of diabetesInsoluble, non-viscous, lessfermentable› Cellulose› Lignins› Psylliuma› Resistant starch› Many hemicellulosesBrown rice, fruits, legumes,seeds, vegetables(cabbage, carrots, brusselssprouts), wheat bran, wholegrains; also extracted andused as food additives› Increase faecal weightand speed faecal passagethrough colon› Provide bulk and feelingsof fullness› Alleviate constipation› Lower risks ofdiverticulosis,haemorrhoids andappendicitis› May help with weightmanagement a Psyllium, a fibre laxative and cereal additive, has both soluble and insoluble properties.Harmful effects of excessive dietary fibre intakeDespite the benefits of dietary fibre to health, a diet high in dietary fibre also has a fewdrawbacks. A person who has a small stomach capacity and eats mostly high-fibre foods maynot be able to take in enough food to meet energy or nutrient needs. The malnourished, theelderly and young children adhering to all-plant (vegan) diets are especially vulnerable tothis problem.Launching suddenly into a high-fibre diet can cause temporary bouts of abdominaldiscomfort, gas and diarrhoea. To prevent such complications, a person adopting a high-fibrediet can take the following precautions:• Increase dietary fibre intake gradually over several weeks to give the GI tract timeto adapt.• Drink plenty of liquids to soften the dietary fibre as it moves through the GI tract.• Select fibre-rich foods from a variety of sources – fruits, vegetables, legumes and wholegrainbreads and cereals.Some dietary fibre can limit the absorption of nutrients by speeding the transit of foodsthrough the GI tract and by binding to minerals. When mineral intake is adequate, however, areasonable intake of high-fibre foods does not seem to compromise mineral balance.Clearly, dietary fibre is like all the nutrients in that ‘more’ is ‘better’ only up to a point.Again, the key words are balance, moderation and variety.RECOMMENDED INTAKES OF STARCH AND DIETARY FIBREDietary guidelines suggest that carbohydrates provide about half (45 to 65 per cent) of theenergy requirement. A person consuming 8000 kilojoules a day should therefore have 3600to 5200 kilojoules of carbohydrate, or about 200 to 325 grams. Because of the importance ofcarbohydrate as an essential energy source, there is no specific recommendation on amountrequired daily. The Australian Dietary Guidelines recommends eating plenty of cereals (includingbreads, rice, pasta and noodles), preferably wholegrain.Recommendations for dietary fibre suggest the same foods just mentioned: whole grains,vegetables, fruits and legumes, which also provide minerals and vitamins. The Nutrient ReferenceTo maximise yourdietary fibre intake:• Eat wholegrainbreakfast cereals.• Eat fruits (such aspears) and vegetables(such as potatoes)with their skins.• Choose wholegrainbreads, brown rice andwholemeal pasta.• Add legumes to soups,salads and casseroles.• Eat fresh and driedfruit for snacks.124 UNDERSTANDING NUTRITIONEleanor, Whitney, et al. Understanding Nutrition, Cengage Australia, 2016. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/think/detail.action?docID=5024519.Created from think on 2021-03-22 18:34:59.Copyright © 2016. Cengage Australia. All rights reserved.Values for Australia and New Zealand recommends eating 25 grams of dietary fibre per day forwomen and 30 grams for men. The average Australian currently eats around 20 grams of dietaryfibre daily.28 One effective way to add fibre is to include plant sources of proteins (legumes) aspart of a well-balanced diet. Table 4.4 presents a list of dietary fibre sources.Adequate intake of dietary fibre:• fosters weight management• lowers blood cholesterol• may help prevent colon cancer• helps prevent and control diabetes• helps prevent and alleviate haemorrhoids• helps prevent appendicitis• helps prevent diverticulitis.Excessive intake of dietary fibre:• displaces energy- and nutrient-dense foods• causes intestinal discomfort and distension• may interfere with mineral absorption.REVIEW ITTABLE 4.4 Dietary fibre in selected foods GrainsWholegrain products provide about 1 to 2 g (or more) of dietary fibre per serving:› 1 slice wholegrain or rye bread› 100 g rolled oatsPolara Studios, Inc.VegetablesMost vegetables contain about 2 to 3 g of dietary fibre per serving:› ½ cup cooked broccoli, brussels sprouts, cabbage, carrots, cauliflower, sweet corn,eggplant, green beans, green peas, mushrooms, parsnips, pumpkin, spinach, sweetpotatoes› ½ cup chopped raw carrots, capsicumPolara Studios, Inc.FruitFresh, frozen and dried fruits have about 2 g of fibre per serving:› 1 medium apple, banana, kiwifruit, nectarine, orange, pear› ½ cup blackberries, blueberries, raspberries, strawberries; fruit juices contain very littledietary fibrePolara Studios, Inc.LegumesMany legumes provide about 6 to 8 g of dietary fibre per serving:› ½ cup cooked baked beans, black beans, black-eyed peas, kidney beans, navy beansSome legumes provide about 5 g of dietary fibre per serving:› ½ cup cooked chickpeas, lentils, split peasPhotoDisc CHAPTER 4 THE CARBOHYDRATES: SUGARS, STARCHES AND DIETARY FIBRE 125Eleanor, Whitney, et al. Understanding Nutrition, Cengage Australia, 2016. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/think/detail.action?docID=5024519.Created from think on 2021-03-22 18:34:59.Copyright © 2016. Cengage Australia. All rights reserved.FROM GUIDELINES TO GROCERIESThe Australian Guide to Healthy Eating recommends several servings of fruits, vegetablesor legumes, and of bread, cereals, rice, pasta or noodles daily as the best way to achieve therecommended amount of carbohydrates and dietary fibre. In selecting high-fibre foods, keep inmind the principle of variety. The dietary fibre in oats lowers cholesterol, whereas that in branhelps promote GI tract health.Bread, cereals, rice, pasta and noodlesBe aware that some foods in this group, especially baked goods such as biscuits, croissants andmuffins, contain added sugars, added fat or both. Aim to select baked products that state they are‘high-fibre’, ‘very high-fibre’, ‘a good source of fibre’, ‘have increased fibre’, ‘are fibre-enriched’or ‘have fibre added’. When selecting from this group of foods, be sure to choose at least halfwholegrain products (see Figure 4.16).AUSTRALIANDIETARYGUIDELINESEnjoy a wide varietyof nutritious foods,including grain(cereal) foods,mostly wholegrainand/or high cerealfibre varieties,such as breads,cereals, rice, pasta,noodles, polenta,couscous, oats,quinoa and barley.FIGURE 4.16 Bread labels comparedFood labels list the quantities of total carbohydrate, dietary fibre and sugars. A close look at these two labels reveals that breadmade from whole-wheat flour provides almost three times as much dietary fibre as the one made mostly from refined flour.Nutrition information SERVINGS PER PACKAGE: 11 (20 SLICES 1 2 CRUSTS)SERVING SIZE: 60 G (2 SLICES)PER SERVING 60 GPER 100 GEnergy589 kJ981 kJProtein5.6 g9.4 gFat› Total1.7 g2.9 g› Saturated0.2 g0.4 g› TransLess than 0.05 gLess than 0.05 g› Polyunsaturated0.7 g1.1 g› Mono-unsaturated0.8 g1.3 gCarbohydrate› Total23.6 g39.4 g› Sugars1.4 g2.4 gDietary fibre9 g15 gSodium293 mg489 mgQuantities stated above are averages only.INGREDIENTSWhole-wheat Wheat Flour, Water, Wheat Flour, Baker’s Yeast,Vinegar, Gluten, Salt, Canola Oil, Emulsifiers (481, 472e, 471), SoyFlour, Sugar, Vitamin (Thiamin). Nutrition information SERVINGS PER PACKAGE: 11 (20 SLICES 1 2 CRUSTS)SERVING SIZE: 60 G (2 SLICES)PER SERVING 60 GPER 100 GEnergy593 kJ989 kJProtein5.5 g9.1 gFat› Total2.3 g3.9 g› Saturated0.3 g0.5 g› TransLess than 0.05 gLess than 0.05 g› Polyunsaturated9.8 g1.4 g› Mono-unsaturated1.1 g1.9 gCarbohydrate› Total22.6 g37.8 g› Sugars1.8 g3.0 gDietary fibre1.8 g6.1 gSodium238 mg397 mgQuantities stated above are averages only.INGREDIENTSWheat Flour, Water, Baker’s Yeast, Vinegar, Salt, Canola Oil,Gluten, Emulsifiers (481, 472e, 471), Soy Flour, Sugar, Vitamin(Thiamin). 126 UNDERSTANDING NUTRITIONEleanor, Whitney, et al. Understanding Nutrition, Cengage Australia, 2016. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/think/detail.action?docID=5024519.Created from think on 2021-03-22 18:34:59.Copyright © 2016. Cengage Australia. All rights reserved.VegetablesThe amount of carbohydrate in a serving of vegetables depends primarily on its starch content.Starchy vegetables – ½ cup of cooked corn, peas or potatoes – provide about 15 grams ofcarbohydrate per serving. A serving of most other non-starchy vegetables – such as a ½ cup ofbroccoli, green beans or tomatoes – provides about 5 grams.FruitA typical fruit serving – a small banana, apple or orange, or ½ cup of most canned or fresh fruit –contains an average of about 15 grams of carbohydrate, mostly as sugars, including the fruitsugar fructose. Fruits vary greatly in their water and dietary fibre contents and, therefore, intheir sugar concentrations.Milks, yoghurt and cheeseA serving (1 cup) of milk or yoghurt provides about 12 grams of carbohydrate. Cottage cheeseprovides about 6 grams of carbohydrate per cup, but most other cheeses contain little, if any,carbohydrate.Meat, fish, poultry, eggs, nuts and legumesWith two exceptions, foods in the meats and meat alternatives group deliver almost nocarbohydrate to the diet. The exceptions are nuts, which provide a little starch and dietary fibrealong with their abundant fat, and legumes, which provide an abundance of both starch anddietary fibre. Just ½ cup serving of lentils provides about 20 grams of carbohydrate, of whichone-third is from dietary fibre.Read food labelsFood labels list the amount, in grams, of total carbohydrate – including starch – per serving andper 100 grams (review Figure 4.16). Dietary fibre (grams) is also listed separately, as are sugars(grams). Sugars reflect both added sugars and those that occur naturally in foods which canmake choosing products with low amounts of added sugars difficult.Clearly a diet rich in complex carbohydrates – starches and dietary fibre – supports efforts tocontrol body weight and prevent heart disease, cancer, diabetes and GI disorders. For these reasons,recommendations urge people to eat plenty of whole grains, vegetables, legumes and fruits – enoughto provide 45 to 65 per cent of the daily energy intake from carbohydrate.REVIEW ITIn today’s world, there is one other reason why plant foods rich in complex carbohydrates andnatural sugars are a better choice than animal foods or foods high in concentrated sweets: ingeneral, less energy and fewer resources are required to grow and process plant foods than toproduce sugar or foods derived from animals.CHAPTER 4 THE CARBOHYDRATES: SUGARS, STARCHES AND DIETARY FIBRE 127Eleanor, Whitney, et al. Understanding Nutrition, Cengage Australia, 2016. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/think/detail.action?docID=5024519.Created from think on 2021-03-22 18:34:59.Copyright © 2016. Cengage Australia. All rights reserved.CHAPTER ACTIVITIESONLINE STUDY TOOLSVisit http://login.cengagebrain.com and use the accesscode that comes with this book for 12 months’ accessto the CourseMate resources and study tools for thischapter:• Complete your Nutrition portfolio• Take the revision quiz• Try out the interactive Nutrition calculations• Watch the Animations• Revisit the chapter with the integrated eBook• Try out an interactive version of the ‘How to’ activities,and more!NUTRITION PORTFOLIOFoods that derive from plants – whole grains, vegetables,legumes and fruits – naturally provide ample carbohydratesand dietary fibre with little or no fat. Refined foods oftencontain added sugars and fat.• List the types and amounts of grain products you eatdaily, making note of which are wholegrain or refinedfoods and how your choices could include morewholegrain options.• List the types and amounts of fruits and vegetablesyou eat daily, making note of how many are darkgreen, orange or deep yellow, how many are starchyor legumes, and how your choices could include moreof these options.• Describe choices you can make in selecting andpreparing foods and beverages to lower your intakeof added sugars.128PUTTING COMMONSENSE TO THE TEST: ANSWERS1 Complex carbohydrates are long chains of monosaccharides joined together. TRUEComplex carbohydrates contain many glucose units and, insome cases, a few other monosaccharides strung together aseither oligosaccharides or larger polysaccharides.2 The majority of carbohydrate digestion occurs in thelarge intestine. FALSEAlthough some digestion occurs in the mouth, the majority ofthe digestion of carbohydrates occurs in the small intestine.3 People who suffer lactose intolerance must avoid alldairy foods. FALSEPeople who suffer lactose intolerance need to managetheir dairy food intake so as to ensure adequate amounts ofcalcium in the diet. Choosing yoghurts and hard cheeses andspreading dairy intake across the day can assist in dietarymanagement of lactose intolerance.4 Glucose fuels the majority of the body’s energy needs.TRUEGlucose fuels the work of most of the body’s cells. Fat andprotein can be used as a fuel source but glucose is the body’spreferred form of fuel.Eleanor, Whitney, et al. Understanding Nutrition, Cengage Australia, 2016. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/think/detail.action?docID=5024519.Created from think on 2021-03-22 18:34:59.Copyright © 2016. Cengage Australia. All rights reserved.CHAPTER 4 THE CARBOHYDRATES: SUGARS, STARCHES AND DIETARY FIBRE 129STUDY QUESTIONSMultiple choice questionsAnswers can be found at the back of the book.1 Carbohydrates are found in virtually all foods except: abcdmilksmeatsbreadsfruits2Monosaccharides include:abcdglucose, fructose and galactoseglucose, maltose and fructoseglucose, glycogen and fructoseglucose, fructose and sucrose 3 The making of a disaccharide from twomonosaccharides is an example of: abcdcondensationgluconeogenesisdigestionhydrolysis4Which carbohydrate is not significantly found infood?abcdfructoseglycogenlactosestarch 5 The significant difference between starch andcellulose is that: abstarch is a polysaccharide, but cellulose is notanimals can store glucose as starch, but not ascellulosehormones can make glucose from cellulose, butnot from starchdigestive enzymes can break the bonds in starch,but not in cellulosecd6The ultimate goal of carbohydrate digestion andabsorption is to yield:abcdenzymesamylasedietary fibreglucose 7 Most carbohydrate digestion occurs in the: abcdmouthstomachpancreassmall intestine8With insufficient glucose in metabolism, fat fragmentscombine to form:abdextrinsmucilages cdphytic acidsketone bodies9What does the pancreas secrete when blood glucoserises and when blood glucose falls?abcdinsulin; glycogenglycogen; adrenalineinsulin; glucagonglucagon; insulin 10 What percentage of the daily energy intake shouldcome from carbohydrates? abcd15 to 2025 to 3045 to 5045 to 65Review questions1Which carbohydrates are described as simple andwhich are complex? (p. 97) 2 Describe the structure of a monosaccharide and namethe three monosaccharides important in nutrition.Name the three disaccharides commonly found infoods and their component monosaccharides. Inwhat foods are these sugars found? (pp. 98–101)3 What happens in a condensation reaction? In ahydrolysis reaction? (p. 100)4 Describe the structure of polysaccharides and namethe ones important in nutrition. How are starch andglycogen similar, and how do they differ? How doesdietary fibre differ from these polysaccharides?(pp. 101–103)5 Why does lactose intolerance occur? How can peoplewith lactose intolerance manage their dairy foodintake? (pp. 107–108)6 How is glucose made from protein? What is thisprocess called? What is meant by the protein­sparingaction of carbohydrate? (pp. 109–110)7 How does the body maintain its blood glucoseconcentration? What happens when the bloodglucose concentration rises too high or falls too low?(pp. 110–112)8 What is meant by glycaemic index? How can thisconcept be used to improve health? (pp. 112–114)9 What are the health effects of starches and dietaryfibre? What are the dietary recommendations regardingthese complex carbohydrates? (pp. 122–124)10 What foods provide starches and dietary fibre?(p. 125)Eleanor, Whitney, et al. Understanding Nutrition, Cengage Australia, 2016. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/think/detail.action?docID=5024519.Created from think on 2021-03-22 18:34:59.Copyright © 2016. Cengage Australia. All rights reserved.130 UNDERSTANDING NUTRITIONNUTRITION CALCULATIONSThese problems will give you practice in doing simplenutrition­related calculations. Although the situationsare hypothetical, the numbers are real, and calculatingthe answers (see the Answers section at the back of thisbook) provides a valuable lesson. Be sure to show yourcalculations for each problem.Health recommendations suggest that 45 to 65 percent of the daily energy intake comes from carbohydrates.Stating recommendations in terms of percentage of energyintake is meaningful only if energy intake is known. Thefollowing exercises illustrate this concept. 1Calculating carbohydrate intakes:aCalculate the carbohydrate intake (in grams) fora student who has a high carbohydrate intake (70 per cent of energy intake) and a moderate energyintake (8000 kJ/day). bNow consider a professor who eats half as muchcarbohydrate as the student (in grams) and has the same energy intake. What percentage doescarbohydrate contribute to the daily intake?c Now consider an athlete who eats twice as muchcarbohydrate (in grams) as the student and has amuch higher energy intake (15 000 kJ/day). Whatpercentage does carbohydrate contribute to thisperson’s daily intake?2 In an attempt to lose weight, a person adopts a dietthat provides 150 grams of carbohydrate per day andlimits energy intake to 4000 kJ. What percentage doescarbohydrate contribute to this person’s daily intake?These exercises should convince you of the importance ofexamining actual intake as well the percentage of energyintake.NUTRITION ON THE NETAnalyse the nutrient composition of foods online: To learnmore about the nutrient content of the foods you eat, you canaccess the full NUTTAB Food Composition Database providedby Food Standards Australia New Zealand from http://www.foodstandards.gov.au/science/monitoringnutrients/nutrientables• Search for ‘lactose intolerance’ at the VictorianGovernment Better Health Channel: http://www.betterhealth.vic.gov.au• Search for ‘sugars’ and ‘fibre’ at the InternationalFood Information Council Foundation site: http://www.ific.org• Learn more about dental caries from the HealthInsitewebpages from the Australian Government Departmentof Health and Ageing: http://www.healthinsite.gov.au• Learn more about diabetes from Diabetes Australia,Diabetes New Zealand and the US National Institute ofDiabetes and Digestive and Kidney Diseases: http://www.diabetesaustralia.com.au, http://www.diabetes.org.nz and http://www.niddk.nih.govSEARCH ME! NUTRITIONKeyword: carbohydrate weight lossTo lose weight, is it more important to reduce carbohydrates or fat? The article Carbohydrates as macronutrients inrelation to protein and fat for body weight control addresses this question. Can weight be lost simply by restricting howmuch fat is eaten? What is the role of different sources of carbohydrate in weight loss?Eleanor, Whitney, et al. Understanding Nutrition, Cengage Australia, 2016. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/think/detail.action?docID=5024519.Created from think on 2021-03-22 18:34:59.Copyright © 2016. Cengage Australia. All rights reserved.CARBS, kJ AND CONTROVERSIES4Carbohydrate-rich foods are easy to like. Mashed potatoes,warm muffins, blueberry pancakes, freshly baked bread,and tasty rice or pasta dishes tempt most people’spalates. In recent years, such foods have been blamed forcausing weight gain and harming health. In contrast, theAustralian Dietary Guidelines recommends eating plenty ofvegetables, legumes, beans, fruit, grain (cereal foods) – allcarbohydrate-rich foods.Do carbohydrate-rich foods cause obesity and relatedhealth problems? Should people ‘cut carbs’ to lose weightand protect their health? Many popular diet books espousea carbohydrate-restricted or carbohydrate-modified diet.Some claim that all or some types of carbohydrates arebad. Some go so far as to equate carbohydrates withtoxic poisons or addictive drugs. ‘Bad’ carbohydrates –such as sugar, white flour and potatoes – are consideredevil because they are absorbed easily and raise bloodglucose. The pancreas then responds by secreting insulin– and insulin is touted as the real villain responsible forour nation’s epidemic of obesity. Whether restrictingoverall carbohydrate intake or replacing certain ‘bad’carbohydrates with ‘good’ carbohydrates, many of thesepopular diets tend to distort the facts. This highlightexamines the scientific evidence behind some of thecurrent controversies surrounding carbohydrates andtheir kilojoules.CARBOHYDRATES’ ENERGYCONTRIBUTIONSThe incidence of obesity in Australia and New Zealand,along with all industrialised and many developingcountries, has risen dramatically over the past severaldecades.1 Popular diet books often blame carbohydratesfor this increase in obesity. One way researchers canexplore whether the amount of carbohydrate in the dietcontributes to increases in body weight over time is byreviewing national food intake survey records, such as theHIGHLIGHTSummarise the key scientific evidence behind some of thecurrent controversies surrounding carbohydrates and theirkilojoules.LEARN IT131United States National Health and Nutrition ExaminationSurvey (NHANES) records. Figure H4.1 presents a summaryof the energy nutrient data that has been compiled in theUnited States over the past three decades. These data showsome remarkable trends. Since the 1970s, energy fromcarbohydrates increased from 42 per cent to 49 per centtoday.2 At the same time, energy from fat dropped from41 per cent to 34 per cent. The percentage of protein intakestayed about the same. Although this is data from theUnited States, many similarities will exist with Australiaand New Zealand.A closer look at the data reveals that, as the percentageof energy from the three energy nutrients shifted slightly,total daily energy intake increased significantly. Ingeneral, as food became more readily available, consumersbegan to eat more than they had in the past. Since the1970s, total energy intakes have increased by about1800 kilojoules a day.3 Almost all of the increase in energycame from an increase in carbohydrate intake. At the same0Daily intake (% kcal/day)Years6010203040501977–1978 1987–1988 1994–1996 2005–2006Key:CarbohydrateFatProteinFIGURE H4.1 Energy nutrients over timeEleanor, Whitney, et al. Understanding Nutrition, Cengage Australia, 2016. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/think/detail.action?docID=5024519.Created from think on 2021-03-22 18:34:59.Copyright © 2016. Cengage Australia. All rights reserved.time, most people were not active enough to use up theextra energy; in fact, estimated activity levels declined overthe same period.4Might too many carbohydrates in the diet be to blamefor weight gains? Interestingly, epidemiological studiesfind an inverse relationship between carbohydrate intakeand body weight.5 Those with the highest carbohydrateintake have the lowest body weight and vice versa. Dietaryfibre, which favours a healthy body weight, explains somebut not all of this relationship.Might a low-carbohydrate diet support weight losses?Studies report that people following low-carbohydratediets do lose weight.6 In fact, they may lose more thanpeople following conventional high-carbohydrate, low-fatdiets – but generally only in the short term. Their latergains make up the difference, so total weight loss is nodifferent after one year. For the most part, weight lossis similar for people following either a low-carbohydratediet or a high-carbohydrate diet. This is an importantpoint. Weight losses reflect restricted kilojoules – not theproportion of energy nutrients in the diet. Any diet canproduce weight loss, at least temporarily, if energy intakeis restricted.SUGARS’ SHARE IN THE PROBLEMOver the past several decades, as obesity rates increasedsharply, consumption of added sugars reached an alltime high. In the United States and Canada, much ofthe rising peak in added sweeteners has come fromhigh-fructose corn syrup.7 High-fructose corn syrup iscomposed of fructose and glucose in a ratio of roughly50:50. Compared with sucrose, high-fructose corn syrupin the United States is less expensive than cane-sugar,easier to use and more stable. In addition to being usedin beverages, high-fructose corn syrup sweetens candies(lollies and sweets), baked goods and hundreds of otherfoods. Fructose contributes about half of the added sugarsin the United States food supply and accounts for about10 per cent of the average energy intake in the UnitedStates. Estimates of the apparent consumption of highfructose corn syrup in Australia and New Zealand suggestthat the intake remains low and is less than 10 per centof additive sweeteners.8 Intakes may be higher in NewZealand as this country allows the importation of coladrinks manufactured in the United States.Although the use of high-fructose corn syrupsweetener parallels unprecedented increases in theincidence of obesity, particularly in the UnitedStates, does it mean that the increasing sugar intakesare responsible for the increase in body fat and itsassociated health problems?9 Excess sugar in the dietmay be associated with more fat on the body. Wheneaten in excess of need, energy from added sugarscontributes to body fat stores, just as excess energy fromother sources does. Added sugars provide excess energy,raising the risk of weight gain. When total energy intakeis controlled, however, moderate amounts of sugar donot cause obesity. Yet moderating sugar intake canbe a challenge. Some claim sugar is addictive. Othersassert sugary beverages are particularly easy to swallowand make it difficult for the body to regulate appetitecontrol and energy metabolism.Cravings and addictionsDo sugars cause cravings and addictions? Foods ingeneral, and carbohydrates and sugars more specifically,are not physically addictive in the ways that drugs are. Yetsome people describe themselves as having ‘carbohydratecravings’ or being ‘sugar addicts’. One frequently notedtheory is that people seek carbohydrates as a way toincrease their levels of the brain neurotransmitterserotonin, which elevates mood. Interestingly, whenthose with self-described carbohydrate cravings indulge,they tend to eat more of everything; the percentage ofenergy from carbohydrates remains unchanged.One reasonable explanation for the carbohydratecravings that some people experience involves the selfimposed labelling of a food as both ‘good’ and ‘bad’ –that is, one that is desirable but should be eaten withrestraint. Restricting intake heightens the desire further(a ‘craving’). Then ‘addiction’ is used to explain whyresisting the food is so difficult and, sometimes, evenimpossible. But the ‘addiction’ is not physiologicalor pharmacological.Simple to swallowIn general, the energy intake of people who drink softdrinks, fruit punches and other sugary beverages isgreater than those who choose differently. For example,people who drink as much as 600 mL or more of sugarsweetened soft drinks daily, can consume an extra1000 kilojoules a day than people who don’t. Not toosurprisingly, they also tend to weigh more.10 Overweightchildren and adolescents tend to consume more sweetdesserts and soft drinks than their normal-weight peerswith a review of the research confirming that consumingsugary beverages correlates with both increased foodenergy and being overweight.11The liquid form of sugar in soft drinks makes itespecially easy to over-consume energy. Swallowingliquid energy requires little effort. These sweetenedbeverages are also cheap and widely available. Theconvenience, economy, availability and flavours ofsugary foods and beverages make overconsumptionespecially likely.Limiting selections of foods and beverages high inadded sugars can be an effective weight-loss strategy,132 UNDERSTANDING NUTRITIONEleanor, Whitney, et al. Understanding Nutrition, Cengage Australia, 2016. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/think/detail.action?docID=5024519.Created from think on 2021-03-22 18:34:59.Copyright © 2016. Cengage Australia. All rights reserved.HIGHLIGHT 4 CARBS, kJ AND CONTROVERSIESespecially when added sugars become an important energysource in their diets. Replacing a can of cola with a glassof water every day, for example, can help a person lose upto 2.5% of their body weight.12 That may not sound likemuch, but it all adds up – and for very little effort.Appetite controlRecall from Chapter 4 that glucose stimulates the releaseof insulin from the pancreas. Insulin, in turn, sets off asequence of hormonal actions that suppress the appetite.(Appetite regulation is discussed fully in Chapter 8.)Fructose, in contrast, does not stimulate the releaseof insulin, and therefore does not suppress appetite.Theoretically, then, eating lots of fructose would neversatisfy a person’s appetite. Although this idea soundsplausible, a major flaw exists: people don’t typically eat purefructose. They eat sucrose or high-fructose corn syrup, andboth of these sugars contain sufficient glucose to stimulatethe release of insulin and suppress appetite accordingly.Whether the meal or snack is liquid or solid may alsoaffect appetite. Even when energy intake is the same, afresh apple suppresses appetite more than apple juice.13Consequently, beverages can influence weight gains bothby providing energy and by not satisfying hunger.Energy regulationOne explanation of why it is so easy to overconsume sugarybeverages is that perhaps the body’s energy regulationsystem cannot detect the energy of sugar in liquid form.Consequently, a person would not compensate forenergy excesses by reducing food intake at other times.A classic research study tested this hypothesis by givingstudents 450-kJ worth of either solid sugars (roughly 40jelly beans) or liquid sugars (about three 375-mL cans ofsoft drinks) to consume daily whenever they chose.14 Itshowed that the energy intake from other foods during‘jelly bean weeks’ was lower – the students ate less food tocompensate for the energy received from the jelly beans.By comparison, energy intake from other foods duringthe ‘soft-drink weeks’ did not decrease – the studentsate their meals without compensating for the kilojoulesin the beverages.Consequently, body weight increasedduring the beverage weeks, but not during the jelly beanweeks. Other studies, however, have found no differencesbetween liquid and solid sugars when examining appetite,energy intake or body weight.15INSULIN’S RESPONSESeveral popular diet books hold insulin responsible for theobesity problem and advocate a low glycaemic diet as theweight-loss solution. Yet, among nutrition researchers,controversy continues to surround the questions ofwhether insulin promotes weight gain or a low glycaemicdiet fosters weight loss.16Recall that just after a meal, blood glucose rises andinsulin responds. How high the insulin levels surge mayinfluence whether the body stores or uses its glucoseand fat supplies. What does insulin do? Among its roles,insulin facilitates the transport of glucose into the cells,the storage of fatty acids as fat and the synthesis ofcholesterol. It is an anabolic hormone that builds andstores, but there’s more to the story. Insulin is only oneof many factors involved in the body’s metabolism ofnutrients and regulation of body weight.Most importantly, insulin is critical to maintaininghealth, as any person with type 1 diabetes can attest.Insulin causes problems only when a person developsinsulin resistance – that is, when the body’s cells donot respond to the large quantities of insulin that thepancreas continues to pump out in an effort to get aresponse. Insulin resistance is a major health problem –but it is not caused by carbohydrate, or by protein, orby fat. It results from being overweight. Importantly,when a person loses weight, insulin response improves,regardless of the diet.The glycaemic index and body weightThe glycaemic index identifies foods that raise bloodglucose and stimulate insulin secretion. What is therelationship between a diet’s glycaemic index and fatstorage? Studies find that diets with a high glycaemicindex are positively associated with body weight.17 Becausefructose does not stimulate insulin secretion, it has a lowglycaemic index. Yet some research suggests that fructosefavours the fat-making pathways and impairs the fatclearing pathways in the body.18 As the liver busily makeslipids, its handling of glucose becomes unbalanced andinsulin resistance develops.19 Research is beginning to findlinks between high fructose intake and prediabetes andthe metabolic syndrome.Might a low glycaemic diet foster weight loss?When obese people followed one of three low-energydiets – high glycaemic diet, low glycaemic diet or highfat diet – for nine months, they all lost about 9 kg.20Furthermore, insulin sensitivity improved for all ofthem. Other studies confirm that overweight peopleexperience similar weight losses on a low-energy dietregardless of whether it has a high or a low glycaemicindex.21 In other words, all low-energy diets supportweight loss; defining the type or amount of carbohydratedoes not enhance losses.133Eleanor, Whitney, et al. Understanding Nutrition, Cengage Australia, 2016. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/think/detail.action?docID=5024519.Created from think on 2021-03-22 18:34:59.Copyright © 2016. Cengage Australia. All rights reserved.HIGHLIGHT ACTIVITIESCRITICAL THINKING QUESTIONSA What is the importance of including carbohydrates inthe diet?B Why do diets low in carbohydrates appear to achievegood weight loss results in the short­term? If youwere to exclude carbohydrates from the diet, whattypes of foods would you not eat? What types of foodswould this leave to select from?As might be expected given the similarity in their chemical composition, high-fructose corn syrup and sucrose produce similareffects in appetite control and energy metabolism. In fact, high-fructose corn syrup is more like sucrose than it is like fructose.Furthermore, people don’t eat pure fructose; they eat foods and drink beverages that contain added sugars – either highfructose corn syrup or sucrose. Limiting these sugars is a helpful strategy when trying to control body weight, but restricting allcarbohydrates would be unwise.The quality of the diet suffers when carbohydrates are restricted. Without fruits, vegetables and whole grains, lowcarbohydrate diets lack not only carbohydrate, but fibre, vitamins, minerals and phytochemicals as well – all dietary factorsprotective against disease. A healthy diet includes a variety of carbohydrate-rich sources: whole-grain cereals, vegetables, legumesand fruits.REVIEW IT134 UNDERSTANDING NUTRITIONEleanor, Whitney, et al. Understanding Nutrition, Cengage Australia, 2016. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/think/detail.action?docID=5024519.Created from think on 2021-03-22 18:34:59.Copyright © 2016. Cengage Australia. All rights reserved.REFERENCESCHAPTERHIGHLIGHT1 K. M. Queenan and co-authors, Concentrated oat b-glucan, afermentable fiber, lowers serum cholesterol in hypercholesterolemicadults in a randomized controlled trial, Nutrition Journal 6 (2007): 6.2 NIH Consensus Development Conference: Lactose intolerance andhealth, http://consensus.nih.gov/2010/lactosestatement.htm3 M. J. Borrok and co-authors, Revisiting the role of glycosylationin the structure of human IgG Fc, Chemical Biology 7 (9) (2012):1596–1602.4 R. L. Schnaar, Glycolipid-mediated cell-cell recognition ininflammation and nerve regeneration, Archives of Biochemistry andBiophysics 426 (2004): 163–172.5 A. B. Walls & A. Schousboe, Brain glycogen: emergency fuel anddynamic function in neurotransmission, Metabolic Brain Disease30 (2015): 249.6 E. L. M. Barr and co-authors, AusDiab 2005: The AustralianDiabetes, Obesity and Lifestyle Study, Melbourne: InternationalDiabetes Institute (2006).7 K. J. Coppell and co-authors, Prevalence of diagnosed andundiagnosed diabetes and prediabetes in New Zealand: findingsfrom the 2008/09 Adult Nutrition Survey. NZ Med J 126.1370(2013): 23–42.8 K. Foster-Powell, S. H. A. Holt and J. C. Brand-Miller, Internationaltable of glycemic index and glycemic load values: 2002, AmericanJournal of Clinical Nutrition 76 (2002): 5–56.9 G. Livesey and co-authors, Is there a dose-response relation ofdietary glycemic load to risk of type 2 diabetes? Meta-analysis ofprospective cohort studies, American Journal of Clinical Nutrition97 (2013): 584–596.10 L. M. Goff and co-authors, Low glycaemic index diets and bloodlipids: a systematic review and meta-analysis of randomisedcontrolled trials, Nutrition, Metabolism, and CardiovascularDiseases 23 (2013): 1–10.11 G. M. Turner-McGrievy and co-authors, Decreases in dietaryglycemic index are related to weight loss among individualsfollowing therapeutic diets for type 2 diabetes, Journal of Nutrition141 (2011): 1469–1474.12 S. D. Ball and co-authors, Prolongation of satiety after low versusmoderately high glycemic index meals in obese adolescents,Pediatrics 111 (2003): 488–494; S. B. Roberts, glycemic index andsatiety, Nutrition in Clinical Care 6 (2003): 20–26.13 M. L. Neuhouser and co-authors, A low-glycemic load diet reducesserum C-reactive protein and modestly increases adiponectin inoverweight and obese adults, Journal of Nutrition 142 (2012): 369–374.14 A. I. Cozma and co-authors, Effect of fructose on glycaemic controlin diabetes: a systematic review and meta-analysis of controlledfeeding trials, Diabetes Care 35 (2012): 1611–1620.15 K. Foster-Powell, S. H. A. Holt and J. C. Brand-Miller, Internationaltable of glycemic index and glycemic load values, American Journalof Clinical Nutrition 76 (2002): 5–56.16 B. M. Popkin and co-authors, The role of high sugar foods andsugar-sweetened beverages in weight gain and obesity, in T. Gill(ed), Managing and Preventing Obesity: Behavioural Factors andDietary Interventions (2014), Cambridge, UK: Elsevier.17 A. Sheiham and W.P.T. James, Diet and dental caries: the pivotalrole of free sugars reemphasized, Journal of Dental Research 94(2015): 1341–1347.18 T. J. McNeill & W.S. Shrapnel, Apparent consumption of refinedsugar in Australia (1938–2011), European Journal of ClinicalNutrition 1 July 2015; doi:10.1038/ejcn.2015.10519 Australian Diabetes Council. Alternative sweeteners. TalkingDiabetes 2 (2012).20 U. A. Ajani, E. S. Ford and A. H. Mokdad, Dietary fiber andC-reactive protein: Findings from National Health and NutritionExamination Survey Data, Journal of Nutrition 134 (2004):1181–1185.21 E. Q. Ye and co-authors, Greater whole-grain intake is associatedwith lower risk of type 2 diabetes, cardiovascular disease, andweight gain, Journal of Nutrition 142 (2012): 1304–1313.22 G. Maconi and co-authors, Treatment of diverticular disease of thecolon and prevention of acute diverticulitis: a systematic review,Diseases of the Colon and Rectum 54 (2011): 1326–1338.23 D. Aune and co-authors, Dietary fibre whole grains and risk ofcolorectal cancer: systematic review and dose-response metaanalysis of prospective studies, British Medical Journal 343(2011): d6617.24 S. A. Bingham and co-authors, Dietary fibre in food and protectionagainst colorectal cancer in the European Prospective Investigationinto Cancer and Nutrition (EPIC): an observational study, Lancet361 (2003): 1496–1501.25 Q. J. Wu and co-authors, Cruciferous vegetables intake and therisk of colorectal cancer: a meta-analysis of observational studies,Annals of Oncology 24(4) (2013): 1079–1087.26 J. I. Barrasa and co-authors, Bile acids in the colon, fromhealthy to cytotoxic molecules, Toxicology in Vitro 27 (2013): 964–977.27 A. J. Wanders and co-authors, Effects of dietary fibre on subjectiveappetite, energy intake and body weight: a systematic review ofrandomized controlled trials, Obesity Reviews 12 (2011): 724–739.28 Better Health Channel, Fibre in Food, http://www.betterhealth.vic.gov.au1 B. Swinburn and A. Wood, Progress on obesity prevention over20 years in Australia and New Zealand, Obesity Reviews 14 (2013):S60–S26.2 U.S. Department of Agriculture, Agricultural Research Service,2008, Nutrient intakes from food, http://www.ars.usda.gov/ba/bhnrc/fsrg.3 W. S. Yancy and co-authors, Trends in energy and macronutrientintakes by weight status over four decades, Public Health Nutrition17 (2014): 256–265.4 Australian Bureau of Statistics, Profiles of Health, Australia 2011–13:overweight and obesity, ABS Catalogue Number 4338.0, Canberra:ABS, (2013).5 G. A. Gaesser, Carbohydrate quantity and quality in relation tobody mass index, Journal of the American Dietetic Association 107(2007): 1768–1780.6 A. M. Johnstone, and co-authors, Effects of a high-protein, lowcarbohydrate v. high-protein, moderate-carbohydrate weight-lossdiet on antioxidant status, endothelial markers and plasma indicesof the cardiometabolic profile, British Journal of Nutrition 106(2011): 282–291.7 V. S. Malik, M. B. Schulze and F. B. Hu, Intake of sugar-sweetenedbeverages and weight gain: a systematic review, American Journal ofClinical Nutrition 84 (2006): 274–288.8 T. J. McNeill & W. S. Shrapnel, Apparent consumption of refinedsugar in Australia (1938–2011), European Journal of ClinicalNutrition (2015); doi:10.1038/ejcn.2015.1059 J. M. Rippe and T. J. Angelopoulos, Sucrose, high-fructose cornsyrup, and fructose, their metabolism and potential healtheffects: what do we really know? Advances in Nutrition 4 (2013):236–245.135Eleanor, Whitney, et al. Understanding Nutrition, Cengage Australia, 2016. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/think/detail.action?docID=5024519.Created from think on 2021-03-22 18:34:59.Copyright © 2016. Cengage Australia. All rights reserved.10 B. Richelsen, Sugar-sweetened beverages and cardio-metabolicdisease risks, Clinical Nutrition and Metabolic Care 16 (2013):478–484.11 V. S. Malik, M. B. Schulze and F. B. Hu, Intake of sugar-sweetenedbeverages and weight gain: a systematic review, American Journal ofClinical Nutrition 84 (2006): 274–288.12 D. F. Tate and co-authors, Replacing caloric beverages with water ordiet beverages for weight loss in adults: main results of the ChooseHealthy Options Consciously Everyday (CHOICE) randomizedclinical trial, American Journal of Clinical Nutrition 95 (2012):555–563.13 R. D. Mattes and W. W. Campbell, Effects of food form and timingof ingestion on appetite and energy intake in lean young adultsand in young adults with obesity, Journal of the American DieteticAssociation 109 (2009): 430–437.14 D. P. DiMeglio and R. D. Mattes, Liquid versus solid carbohydrate:Effects on food intake and body weight, International Journal ofObesity and Related Metabolic Disorders 24 (2000): 794–800.15 S. Soenen and M. S. Weterterp-Plantenga, No differences insatiety or energy intake after high-fructose corn syrup, sucrose, ormilk preloads, American Journal of Clinical Nutrition 86 (2007):1586–1594.16 R. Clemens and P. Pressman, Clinical value of glycemic indexunclear, Food Technology 58 (2004): 18; M. A. Pereira andco-authors, Effects of a low-glycemic load diet on restingenergy expenditure and heart disease risk factors during weightloss, Journal of the American Medical Association 292 (2004):2482–2490; A. Raben, Should obese patients be counselled tofollow a low-glycaemic index diet? No, Obesity Reviews 3 (2002):245–256; D. B. Pawlak, C. B. Ebbeling and D. S. Ludwig, Shouldobese patients be counselled to follow a low-glycaemic index diet?Yes, Obesity Reviews 3 (2002): 235–243.17 O. Gogebakan and co-authors, Effects of weight loss and long-termweight maintenance with diets varying in protein and glycemicindex on cardiovascular risk factors: The Diet, Obesity, and Genes(DiOGenes) Study: a randomized, controlled trial, Circulation 124(2011): 2829–2838.18 E. J. Parks and co-authors, Dietary sugars stimulate fattyacid synthesis in adults, Journal of Nutrition 138 (2008):1039–1046.19 C. A. Lyssiotis and L. C. Cantley, Metabolic syndrome: F stands forfructose and fat, Nature 502 (2013): 181–182.20 S. K. Raatz and co-authors, Reduced glycemic index and glycemicload diets do not increase the effects of energy restriction on weightloss and insulin sensitivity in obese men and women, Journal ofNutrition 135 (2005): 2387–2391.21 R. Sichieri and co-authors, An 18-mo randomized trial of a lowglycemic-index diet and weight change in Brazilian women,American Journal of Clinical Nutrition 86 (2007): 707–713;S. K. Das and co-authors, Long-term effects of 2 energy-restricteddiets differing in glycemic load on dietary adherence, bodycomposition, and metabolism in CALERIE: a 1-y randomizedcontrolled trial, American Journal of Clinical Nutrition 85 (2007):1023–1030.136 UNDERSTANDING NUTRITIONEleanor, Whitney, et al. Understanding Nutrition, Cengage Australia, 2016. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/think/detail.action?docID=5024519.Created from think on 2021-03-22 18:34:59.Copyright © 2016. Cengage Australia. All rights reserved.