SOLUTION: Nutrient Reference Values | My Assignment Tutor

The following is an extract from:Nutrient Reference Values for Australia and New ZealandIncluding Recommended Dietary IntakesENDORSED BY THE NHMRC ON 9 SEPTEMBER 2005© Commonwealth of Australia 2006ISBN Print 1864962372ISBN Online 1864962437The Nutrient Reference Values (NRVs) was a joint initiative of the Australian National Health and MedicalResearch Council (NHMRC) and the New Zealand Ministry of Health (MoH). The NHMRC would like tothank the New Zealand MoH for allowing the use of the NRV material in the development of this website.NHMRC publications contact:Email: nhmrc.publications@nhmrc.gov.auInternet: http://www.nhmrc.gov.auFree Call: 1800 020 103 ext 9520PROTEINPROTEINBACKGROUNDProtein occurs in all living cells and has both functional and structural properties. Amino acids,assembled in long chains, are the building blocks of protein. Of the 20 amino acids found in proteins,some can be made by the body while others are essential in the diet. Amino acids are used for thesynthesis of body proteins and other metabolites and can also be used as a source of dietary energy.The proteins of the body are continually being broken down and resynthesised in a process calledprotein turnover.Protein is the body’s main source of nitrogen which accounts for about 16% the weight of protein.Non-protein nitrogenous compounds are usually present in the diet in minimal amounts. Thus, inassessing dietary protein sources, the total amount of protein, its digestibility and its content of essentialamino acids need to be considered. Proteins also contain carbon, oxygen, hydrogen and, to a lesserextent, sulphur.The nine indispensable or essential amino acids, defined as those that the body is unable to synthesisefrom simpler molecules, are histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine,tryptophan and valine. Cysteine and tyrosine can partly replace methionine and phenylalanine,respectively. Under certain extreme physiological conditions such as in prematurity or during somecatabolic illnesses, the non-essential amino acids arginine, cysteine, glutamine, glycine, proline andtyrosine may be required in the diet. Under normal conditions, glutamine, glutamate or aspartate cansupply arginine; methionine and serine can be converted to cysteine; glutaminic acid and ammonia canbe converted to glutamine; serine or choline can supply glycine; glutamate can provide proline andphenylalanine can be converted to tyrosine. These amino acids are sometimes termed conditionallyindispensable. Alanine, aspartic acid, asparagine, glutamic acid and serine are non-essential. The aminoacids act as precursors for many coenzymes, hormones, nucleic acids and other molecules.Proteins in the diet and the body are associated with a number of other vitamins and minerals and aremore complex and variable than other energy sources such as fat and carbohydrate. The polypeptidechains that make up proteins are folded into three-dimensional structures that include helical regionsand sheet-like structures due to interaction between the amino acids in the chain. The final shape ofa mature protein often reflects its function and also interactions with other molecules. The protein’sstructure may influence its digestibility.The body of a 76 kg man contains about 12 kg of protein. Nearly half of this protein is present asskeletal muscle, while other structural tissues such as blood and skin contain about 15% (Lentner 1981).Myosin, actin, collagen and haemoglobin account for almost half of the body’s total protein content.Only 1% of the body’s store is labile (Waterlow 1969, Young et al 1968), so its availability as a reserveenergy store, compared to body fat, is limited. Unlike carbohydrate and fats, the body does not maintainan energy storage form of protein.Proteins are found in both animal and plant foods. The amino acid profile of animal proteins is closer tothat of humans but all of the necessary amino acids can be provided in the amounts needed from plantsources. The major sources in the Australian and New Zealand diet are meat, poultry and fish (about33%), cereals and cereal-based foods (about 25%) and dairy foods (about 16%). Vegetables also provideabout 8%. Certain proteins can cause allergic responses in some individuals notably milk, eggs, peanutsand soy in children and fish, shellfish, peanuts and tree nuts in adults.Nutrient Reference Values for Australia and New Zealand 29PROTEINThe efficiency of dietary protein digestion is high. After ingestion, proteins are denatured by acid in thestomach and cleaved to smaller peptides. A number of gut enzymes including trypsin, chymotrypsin,elastase and carboxypeptidases, complete the process. The free amino acids and small peptides thatresult are absorbed into the mucosa by specific carrier systems. After intracellular hydrolysis of absorbedpeptides, free amino acids are secreted to the portal blood where some of the amino acids are taken upand the remainder pass into systemic circulation for delivery to, and use by, peripheral tissues.There is wide variation in dietary protein intake, to which the body is able to adapt over a few days.However, severe disease states or fasting can cause substantial body protein losses as energy needstake priority. The protein lost is, however, also necessary to the functioning of the body. A seriousdepletion in the body mass protein can be life threatening with muscle loss, including loss of heartmuscle (Hansen et al 2000). Thus, not only must sufficient protein be provided for sustenance, but alsosufficient non-protein energy so the carbon skeletons of amino acids are spared from providing energy.Similarly, unless amino acids are present in the right balance, protein utilisation will be compromised(Duffy et al 1981). Protein-energy malnutrition (PEM) is common on a worldwide basis in both childrenand adults (Stephenson et al 2000) causing the death of 6 million children a year (FAO 2000). Incountries like Australia and New Zealand, PEM is seen most commonly associated with other diseasesand in the elderly. Protein deficiency affects all organs including the developing brain (Pollitt 2000), aswell as the immune system (Bistrian 1990) and gut mucosal function (Reynolds et al 1996).There are two key methods for assessing protein requirements, factorial methods and nitrogen balance.For infants, the amount provided by the milk of healthy mothers is used to estimate the adequate intake.RECOMMENDATIONS BY LIFE STAGE AND GENDER InfantsAIProtein0–6 months10 g (1.43 g/kg body weight)7–12 months14 g (1.60 g/kg body weight) Rationale: An AI for protein for 0–6 months was calculated by multiplying together the average intakeof breast milk (0.78 L/day) and the average concentration of protein in breast milk of 12.7 g/L (Deweyet al 1983, 1984, Butte et al 1984, Nommsen et al 1991, Mitoulas et al 2002) and rounding. An AI forinfants aged 7 to 12 months was calculated by multiplying the concentration of protein in breast milkat this stage of lactation of 11 g/L (Dewey et al 1984, Mitoulas et al 2002, Nommsen et al 1991) by thevolume of breast milk (0.6 L) and adding an allowance for complementary foods of 7.1 g/day from theUS, NHANES III data (FNB:IOM 2002) to give an AI of 14 g/day (or 1.6 g/kg body weight/day, assuminga reference weight of 9 kg). It is important that the digestibility and comparative protein quality offormulas is taken into account as these will be different to human milk.Children & adolescents EAR RDI ProteinAll 1–3 yr4–8 yrBoys9–13 yr14–18 yrGirls9–13 yr14–18 yr12 g/day (0.92 g/kg)16 g/day (0.73 g/kg)14 g/day (1.08 g/kg)20 g/day (0.91 g/kg)31 g/day (0.78 g/kg)49 g/day (0.76 g/kg)40 g/day (0.94 g/kg)65 g/day (0.99 g/kg)24 g/day (0.61 g/kg)35 g/day (0.62 g/kg)35 g/day (0.87 g/kg)45 g/day (0.77 g/kg) 30 Nutrient Reference Values for Australia and New ZealandPROTEINRationale: There are limited data on which to estimate EARs for children and adolescents.Requirements were estimated using the factorial method including estimates of the amount needed forgrowth and maintenance on a fat-free mass basis. An overall CV of 12% for the EAR was used to derivethe RDI.Adults EAR RDI ProteinMen 19–30 yr31–50 yr51–70 yr>70 yrWomen19–30 yr31–50 yr51–70 yr>70 yr52 g/day (0.68 g/kg)52 g/day (0.68 g/kg)52 g/day (0.68 g/kg)65 g/day (0.86 g/kg)64 g/day (0.84 g/kg)64 g/day (0.84 g/kg)64 g/day (0.84 g/kg)81g/day (1.07 g/kg)37 g/day (0.60 g/kg)37 g/day (0.60 g/kg)37 g/day (0.60 g/kg)46 g/day (0.75 g/kg)46 g/day (0.75 g/kg)46 g/day (0.75 g/kg)46 g/day (0.75 g/kg)57 g/day (0.94 g/kg) Rationale: There are limited data except for younger adult males. Requirements were estimated usingthe factorial method including estimates of the amount needed for growth and maintenance on a fat-freemass basis. An overall CV of 12% was used to derive the RDIs. Adults older than 53 years appeared tohave 25% higher requirements for maintenance than younger adults in an analysis by Rand et al (2003).However, there were only 14 subjects and the difference did not reach significance. Other researchersfrom the same institute have also suggested a need for higher intakes in older adults (Campbell & Evans1996, Campbell et al 2001). For this reason, the EAR for adults >70 years was increased by 25% over thatof younger adults, although it should be recognised that the data supporting this increase are limited.The RDI is estimated assuming a CV of 12% for the EAR based on the analysis of Rand et al (2003).Pregnancy EAR RDI Protein(2nd and 3rd trimesters) 14–18 yr19–30 yr31–50 yr47 g/day (0.82 g/kg)49 g/day (0.80 g/kg)49 g/day (0.80 g/kg)58 g/day (1.02 g/kg)60 g/day (1.00 g/kg)60 g/day (1.00 g/kg) Rationale: No additional requirement was set for the first trimester as there is little additional weightgain during this time. The recommendations are for the second and third trimesters. One third of thepregnancy weight gain occurs in the second trimester and two thirds in the third trimester. The increasein body weight requires an additional 0.2 g/kg/day during this phase of pregnancy based on themid-trimester weight gain and efficiency of utilisation observed in the meta analysis of Rand et al(2003), making the EAR at this stage of 0.8 g/kg/day. The RDI is estimated using a CV of 12% for theEAR giving an RDI in the second and third trimesters of pregnancy of 1.00–1.02 g/kg/day or 60 g/daywith rounding.Lactation EAR RDI Protein 14–18 yr19–30 yr31–50 yr51 g/day (0.90 g/kg)54 g/day (0.88 g/kg)54 g/day (0.88 g/kg)63 g/day (1.1 g/kg)67 g/day (1.1 g/kg)67 g/day (1.1 g/kg) Nutrient Reference Values for Australia and New Zealand 31PROTEINRationale: Using a factorial approach, the additional requirement in pregnancy was estimated as21.2 g/day (FNB:IOM 2002), assuming that all nitrogen in human milk is provided by extra protein.This was the figure used by the US:Canadian Committee. However, about 20–25% of the nitrogen inmilk is non-protein and can be provided by the unused portion of the maintenance protein intake.On this basis, the additional need is about 17 g/day or 0.28 mg/kg body weight. The RDI was setassuming a CV of 12% for the EAR.UPPER LEVEL OF INTAKE – PROTEINNo UL was set as there are insufficient data. However, a UL of 25% protein as energy isrecommended for which the rationale is provided in the ‘Chronic disease’ section of thisdocument.Rationale: Humans consume widely varying amounts of proteins. Although some adverse effectshave been reported with moderate to high levels of supplementation, the risk of adverse effects fromfoods consumed as part of everyday diets is very low. This consideration, together with the limiteddata available, makes it impossible to set an upper limit in terms of grams per day. However cautionis needed. Intakes of individual amino acids that may be consumed as supplements should not exceedthose normally found in the diet.REFERENCESAustralian Bureau of Statistics/Commonwealth Department of Health and Ageing. National NutritionSurvey: Nutrient intakes and physical measurements. Australia, 1995. Canberra: Australian Bureauof Statistics, 1998.Bistrian BR. Recent advances in parenteral and enteral nutrition: a personal perspective. J ParenteralEnteral Nutr 1990;14:329–34.Butte NF, Garza C, Johnson CA, O’Brian Smith E, Nichols BL. Longitudinal changes in milk compositionof mothers delivering preterm and term infants. Early Hum Dev 1984;9:153–62.Campbell WW, Evans WJ. Protein requirements of elderly people. Eur J Clin Nutr 1996;50:S180–S185.Campbell WW, Trappe TA, Wolfe RR, Evans WJ. The recommended dietary allowance for protein maynot be adequate for older people to maintain skeletal muscle. J Gerontol A Biol Med Sci 2001;56:M373–M380.Dewey KG, Finley DA, Lonnerdal B. Breast milk volume and composition during late lactation(7-20 months). J Pediatr Gastroenterol Nutr 1984;3:713–20.Dewey KG, Lonnerdal B. Milk and nutrient intake of breast-fed infants from 1 to 6 months: relation togrowth and fatness. J Pediatr Gastroenterol Nutr 1983;2:497–506.Duffy B, Gunn T, Collinge J, Penchartz PB. The effect of varying protein quality and energy intake onthe nitrogen metabolism of parenterally fed very low birth weight (