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14-September-2008 18:38:41 - value Biological value BV is a measure of the proportion of absorbed protein from a food which becomes incorporated into the proteins of the organism's body. It summarises how readily the broken down protein can be used in protein synthesis in the cells of the organism. Proteins are the major source of nitrogen food, unlike carbohydrates and fats. This method assumes protein is the only source of nitrogen and measures the proportion of this nitrogen absorbed by the body which is then excreted. The remainder must have been incorporated into the proteins of the organisms body. A ratio of nitrogen incorporated into the body over nitrogen absorbed gives a measure of protein 'usability' - the BV. Unlike some measures of protein usability, biological value does not take into account how readily the protein can be digested and absorbed largely by the small intestine. This is reflected in the experimental methods used to determine BV. BV, confusingly, uses two similar scales: The true percentage utilization usually shown with a percent symbol. The percentage utilization relative to a readily utilizable protein source, often egg usually shown as unitless. These two values will be similar but not identical. The BV of a food varies greatly, and depends on a wide variety of factors. In particular the BV value of a food varies depending on its preparation and the recent diet of the organism. This makes reliable determination of BV difficult and of limited use - fasting prior to testing is universally required in order to make the values reliable. BV is commonly used in nutrition science in many mammalian organisms, and is a relevant measure in humans.1 It is a popular guideline in bodybuilding in protein choice.23 Contents 1 Determination of BV 1.1 Percentage utilization 1.2 Relative utilization 1.3 Conversion 2 Factors which affect BV 2.1 Properties of the protein source 2.2 Properties of the test species or individual 2.2.1 Under test conditions 2.2.2 In everyday life 2.3 Factors with no effect 3 Advantages and disadvantages 3.1 In comparison to other methods 4 In animals 5 Typical values 6 Criticism 7 See also 8 References Determination of BV For accurate determination of BV:4 the test organism must only consume the protein or mixture of proteins of interest the test diet. the test diet must contain no non-protein sources of nitrogen. the test diet must be of suitable content and quantity to avoid use of the protein primarily as an energy source. These conditions mean the tests are typically carried out over the course of over one week with strict diet control. Fasting prior to testing helps produce consistency between subjects it removes recent diet as a variable. There are two scales on which BV is measured; percentage utilization and relative utilization. By convention percentage BV has a percent sign % suffix and relative BV has no unit. Percentage utilization Biological value is determined based on this formula.45 BV = Nr / Na 100 Where: Na = nitrogen absorbed in proteins on the test diet Nr = nitrogen incorporated into the body on the test diet However direct measurement of Nr is essentially impossible. It will typically be measured indirectly from nitrogen excretion in urine.6 Faecal excretion of nitrogen must also be taken into account - this protein is not absorbed by the body and so not included in the calculation of BV. BV = Ni - Nef - Neu - Nb / Ni - Nef 100 Where: Ni = nitrogen intake in proteins on the test diet Nef = nitrogen excreted in faeces whilst on the test diet Neu = nitrogen excreted in urine whilst on the test diet Nb = nitrogen excreted on a protein free diet Note: Nr = Ni - Nef - Neu - Nb Na = Ni - Nef This can take any value of 100 or less, including negative. A BV of 100% indicates complete utilization of a dietary protein, ie. 100% of the protein ingested and absorbed is incorporated into proteins into the body. Negative values are possible if excretion of nitrogen exceeds intake in proteins. All non-nitrogen containing diets have negative BV. The value of 100% is an absolute maximum, no more than 100% of the protein ingested can be utilized in the equation above Neu, Nef and Nb cannot go negative, setting 100% as the maximum BV. Relative utilization Due to experimental limitations BV is often measured relative to an easily utilizable protein. Normally egg protein is assumed to be the most readily utilizable protein and given a BV of 100. For example: Two tests of BV are carried out on the same person; one with the test protein source and one with a reference protein egg protein. relative BV = BVtest / BVegg 100 Where: BVtest = percentage BV of the test diet for that individual BVegg = percentage BV of the reference egg diet for that individual This is not restricted to values of less than 100. The percentage BV of egg protein is only 93.7% which allows other proteins with true percentage BV between 93.7% and 100% to take a relative BV of over 100. For example, whey protein takes a relative BV of 104, while its percentage BV is under 100%. The principal advantage of measuring BV relative to another protein diet is accuracy; it helps account for some of the metabolic variability between individuals. In a simplistic sense the egg diet is testing the maximum efficiency the individual can take up protein, the BV is then provided as a percentage taking this as the maximum. Conversion Providing it is known which protein measurements were made relative to it is simple to convert from relative BV to percentage BV: BVpercentage = BVrelative / BVreference 100 BVrelative = BVpercentage / 100 BVreference Where: BVrelative = relative BV of the test protein BVreference = percentage BV of reference protein typically egg: 93.7%. BVpercentage = percentage BV of the test protein While this conversion is simple it is not strictly valid due to the differences between the experimental methods. It is, however, suitable for use as a guideline. Factors which affect BV The determination of BV is carefully designed to accurately measure some aspects of protein usage whilst eliminating variation from other aspects. When using the test or considering BV values care must be taken to ensure the variable of interest is quantified by BV. Factors which affect BV can be grouped into properties of the protein source and properties of the species or individual consuming the protein. Properties of the protein source Three major properties of a protein source affect its BV: Amino acid composition, and the limiting amino acid, which is usually lysine Preparation cooking Vitamin and mineral content Amino acid composition is the principal effect. All proteins are made up of combinations of the 21 biological amino acids. Some of these can be synthesised or converted in the body, whereas others cannot and must be ingested in the diet. These are known as essential amino acids EAAs, of which there are 9 in humans. The number of EAAs varies according to species see below. EAAs missing from the diet prevent the synthesis of proteins that require them. If a protein source is missing critical EAAs, then its biological value will be low as the missing EAAs form a bottleneck in protein synthesis. For example, if a hypothetical muscle protein requires phenylalanine an essential amino acid, then this must be provided in the diet for the muscle protein to be produced. If the current protein source in the diet has no phenylalanine in it the muscle protein cannot be produced, giving a low usability and BV of the protein source. In a related way if amino acids are missing from the protein source which are particularly slow or energy consuming to synthesise this can result in a low BV. Methods of food preparation also have an impact on availability of amino acids in a food source. Some of food preparation may damage or destroy some EAAs, reducing the BV of the protein source. Many vitamins and minerals are vital for the correct function of cells in the test organism. If critical minerals or vitamins are missing from the protein source this can result in a massively lowered BV. Many BV tests artificially add vitamins and minerals for example in yeast extract to prevent this. Properties of the test species or individual Under test conditions Variations in BV under test conditions are dominated by the metabolism of the individuals or species being tested. In particular differences in the essential amino acids EAAs species to species has a significant impact, although even minor variations in amino acid metabolism individual to individual have a large effect. The fine dependence on the individual's metabolism makes measurement of BV a vital tool in diagnosing some metabolic diseases. In everyday life The principal effect on BV in everyday life is the organism's current diet, although many other factors such as age, health, weight, sex, etc. all have an effect. In short any condition which can affect the organism's metabolism will vary the BV of a protein source. In particular, whilst on a high protein diet the BV of all foods consumed is reduced - the limiting rate at which the amino acids may be incorporated into the body is not the availability of amino acids but the rate of protein synthesis possible in cells. This is a major point of criticism of BV as a test; the test diet is artificially protein rich and may have unusual effects. Factors with no effect BV is designed to ignore variation in digestibility of a food - which in turn largely depends on the food preparation. For example compare raw soy beans and extracted soy bean protein. The raw soy beans, with tough cell walls protecting the protein, have a far lower digestibility than the purified, unprotected, soy bean protein extract. As a foodstuff far more protein can be absorbed from the extract than the raw beans, however the BV will be the same. The exclusion of digestibility is a point of misunderstanding and leads to misrepresentation of the meaning of a high or low BV. Advantages and disadvantages BV provides a good measure of the usability of proteins in a diet and also plays a valuable role in detection of some metabolic diseases. BV is, however, a scientific variable determined under very strict and unnatural conditions. It is not a test designed to evaluate the usability of proteins whilst an organism is in everyday life - indeed the BV of a diet will vary greatly depending on age, weight, health, sex, recent diet, current metabolism, etc. of the organism. In addition BV of the same food varies significantly species to species. Given these limitations BV is still relevant to everyday diet to some extent. No matter the individual or their conditions a protein source with high BV, such as egg, will always be more easily used than a protein source with low BV. In comparison to other methods There are many other major methods of determining how readily used a protein is, including: Net protein Utilization NPU Protein Efficiency Ratio PER Nitrogen Balance NB Protein digestibility PD Protein Digestibility Corrected Amino Acid Score PDCAAS These all hold specific advantages and disadvantages over BV,7 although in the past BV has been held in high regard.89 In animals The Biological Value method is also used for analysis in animals such as cattle, poultry, and various laboratory animals such as rats. It was used by the poultry industry to determine which mixtures of feed were utilized most efficiently by developing chicken. Although the process remains the same, the biological values of particular proteins in humans differs from their biological values in animals due to physiological variations.10 Typical values Common foodstuffs and their values: Note: this scale uses 100 as 100% of the nitrogen incorporated. Isolated Whey: 100citation needed Whole bean: 9611 Whole Soy Bean: 96 11 Human milk: 9512 Chicken egg: 9412 Soybean milk: 9111 Cow milk: 9012 Cheese: 8413 Rice: 8313 Defatted soy flour: 8111 Fish: 7614 Beef: 74.314 Immature bean: 6511 Full-fat soy flour: 6411 Soybean curd tofu: 6411 Whole wheat: 6414 White flour: 4111 Common foodstuffs and their values: 15 Note: These values use whole egg as a value of 100, so foodstuffs that provide even more nitrogen than whole eggs, can have a value of more that 100. 100, does not mean that 100% of the nitrogen in the food is incorporated into the body, and not excreted, as in in other charts. Whey protein concentrate: 104 Whole egg: 100 Cow milk: 91 Beef: 80 Casein: 77 Soy: 74 Wheat gluten: 64 Criticism Since the method measures only the amount that is retained in the body critics have pointed out what they perceive as a weakness of the biological value methodology.16 Critics have pointed to research that indicates that because whey protein isolate is digested so quickly it may in fact enter the bloodstream and be converted into carbohydrates through a process called gluconeogenesis much more rapidly than was previously thought possible, so while amino acid concentrations increased with whey it was discovered that oxidation rates also increased and a steady-state metabolism, a process where there is no change in overall protein balance, is created.17 They claim that when the human body consumes whey protein it is absorbed so rapidly that most of it is sent to the liver for oxidation. Hence they believe the reason so much is retained is that it is used for energy production not protein synthesis. This would bring into question whether the method defines which proteins are more biologically utilizable. A further critique published in the Journal of Sports Science and Medicine states that the BV of a protein does not take into consideration several key factors that influence the digestion and interaction of protein with other foods before absorption, and that it only measures a proteins maximal potential quality and not its estimate at requirement levels.18 Also, the study by Poullain et al, which is often cited to demonstrate the superiority of whey protein hydrolysate by marketers, measured nitrogen balance in rats after three days of starvation, which corresponds to a longer period in humans.19 The study found that whey protein hydrolysate led to better nitrogen retention and growth than the other proteins studied. However the study's flaw is in the BV method used, as starvation affects how well the body will store incoming protein as does a very high caloric intake, leading to falsely elevated BV measures.20 So, the BV of a protein is related to the amount of protein given. BV is measured at levels below the maintenance level. This means that as protein intake goes up, the BV of that protein goes down. For example, milk protein shows a BV near 100 at intakes of 0.2 g/kg. As protein intake increases to roughly maintenance levels, 0.5 g/kg, BV drops only around 70.20 Another limitation of the use of Biological Value as a measure of protein quality is that proteins which are completely devoid of one essential amino acid EAA can still have a BV of up to 40. This is because of the ability of organisms to conserve and recycle EAAs as an adaptation of inadequate intake of the amino acid.21 Lastly, the use of rats for the determination of protein quality is not ideal. Rats differ from humans in requirements of essential amino acids. This has led to a general criticism that experiments on rats lead to an over-estimation of the BV of high-quality proteins to man because human requirements of essential amino acids are much lower than those for rats as rats grow at a much faster rate than humans. Also, because of their fur, rats are assumed to have relatively high requirements of sulphur-containing amino acids methionine and cysteine. As a result, the analytical method that is universally recognized by the FAO/WHO as well as the FDA, USDA, United Nations University UNU and the National Academy of Sciences when judging the quality of protein in the human is not PER or BV but the Protein Digestibility Corrected Amino Acid Score PDCAAS, as it is viewed as accurately measuring the correct relative nutritional value of animal and vegetable sources of protein in the diet.2223 However, scientific studies demonstrate that the PDCAAS scale has limitations in predicting protein quality of those protein sources which may contain naturally occurring growth-depressing factors or antinutritional factors formed during alkaline and/or heat processing. In short, PDCAAS makes no distinction of their performance relative to each other because after they pass a certain point their scores are all capped at the maximum 1.0 and receive an identical rating.242526 This is because in 1990 at an FAO/WHO meeting it was decided that proteins having values higher than 1.0 would be rounded or leveled down to 1.0 as scores above 1.0 are considered to indicate that the protein contains essential amino acids in excess of the human requirements.27 This approach implies injustice to high-quality proteins which can compensate for low-quality ones by virtue of their high content of essential amino acids egg has an actual PDCAA score of 1.19 compared to 0.91 for soy, however when leveled down, they appear much closer.28 Regardless, the scientific community has raised critical questions about the validity of PDCAAS.specify293031 See also Edible protein per unit area of land References ^ Thomas, K. Ueber die biologische Wertigkeit der stickstoff-substanzen in 1909 verschiedenen Nahrungsmitteln. Arch. Physiol., 219. ^ Optimum Sports Nutrition: Your Competitive Edge, A Complete Nutritional Guide For Optimizing Athletic Performance; Chapter 12. by Dr. Michael Colgan ^ The Great Animal Versus Vegetable Protein Debate What Is The Best Protein For Muscle Growth? ^ a b Mitchell, H.H. 1923. A Method of Determining the Biological Value of Protein. Journal of Biol. Chem. 58 3: 873. ^ Chick H., Roscoe, M.H. 1930. The biological values of proteins: A method for measuring the nitrogenous exchange of rats for the purpose of determining the biological value of proteins. Biochem J. 24 6: 1780-2. ^ Fixsen, M.A.B. The biological value of purified caseinogen and the influence of vitamin B2 upon biological values, determined by the balance sheet method. Biochem J. 1930; 246: 1794-1804. ^ The Use Of Biological Value Of A Protein In Evaluating Its Quality For Human Requirments ^ Mitchell, H.H. A method for determining the biological value of protein. 1924 J. Biol. Chem., 58, 873. http://www.jbc.org/cgi/reprint/58/3/873.pdf ^ Mitchell, H.H. and G.G. Carman. The biological value of the nitrogen of mixtures 1926 of patent white flour and animal foods. J. Biol. Chem., 68, 183. ^ Recent developments in protein quality evaluation by Dr E. Boutrif. ^ a b c d e f g h YourCause.com ^ a b c http://www.medbio.info/Horn/Time%206/protei4.gif ^ a b Jolliet, P. Enteral nutrition in intensive care patients: a practical approach. Intensive Care Medicine 1998. ^ a b c Microsoft PowerPoint - The Nutritious Egg ^ Protein, Which Is Best., JSSM. Retrieved on 2007-10-31. ^ Joint FAO/WHO/UNU Expert Consultation on Energy and Protein Requirements, The use of biological value of protein in evaluatiing its quality for human requirements, S.G. Srikantia, University of Mysore. ^ Testosterone Nation, The Protein Roundtable, August 24, 2000. ^ Journal of Sports Science and Medicine 2004 3, 118-130 ^ Poullain, MG et al. Effect of whey proteins, their oligopeptide hydrosylates and free amino acid mixtures on growth and nitrogen retention in fed and starved rats. J Parenteral and Enteral Nutrition 1989 13: 382-386 ^ a b Pellett, PL and Young, VR. Nutritional evaluation of protein foods. United Nations University, 1980. ^ Said, A.K. and Hegsted, D.M., J. Nutr., 99, 474, 1969 ^ FAO/WHO 1991 Protein Quality Evaluation Report of Joint FAO/WHO Expert Consultation, Food and Agriculture Organization of the United Nations, FAO Food and Nutrition Paper No. 51, Rome. ^ Schaafsma, G. 2000 'The protein digestibility-corrected amino acid score. Journal of Nutrition 130, 1865S-1867S ^ The Journal of Sports Science and Medicine 2004 3, 118-130.. ^ Sarwar G. Health Canada, Bureau of Nutritional Sciences, Banting Research Centre, Ottawa, Ontario. The protein digestibility-corrected amino acid score method overestimates quality of proteins containing antinutritional factors and of poorly digestible proteins supplemented with limiting amino acids in rats. J Nutr. 1997 May;1275:758-64. Pub Med Reference ^ Schaafsma G. TNO Nutrition and Food Research, PO Box 360, 3700 AJ Zeist, The Netherlands. The Protein Digestibility-Corrected Amino Acid Score PDCAAS--a concept for describing protein quality in foods and food ingredients: A Critical Review. J AOAC Int. 2005 May-Jun;883:988-94. The Validity Of PDCAAS Under Critical Review ^ FAO/WHO 1990. Expert consultation on protein quality evaluation. Food and Agriculture Organization of the United Nations, Rome. ^ FAO/WHO/UNU 1985. Expert consultation. Energy and protein requirements. Technical Report Series 724. World Health Organization, Geneva. ^ Gertjan Schaafsma; Center of Expertise Nutrition, DMV International-Campina Melkunie, 6700 AA, Wageningen, the Netherlands The Protein Digestibility-Corrected Amino Acid Score -- Journal of Nutrition. 2000;1307:1865S-1867S. The Journal of Nutrition ^ Darragh A. J., Schaafsma G., and Moughan P. J. Impact of amino acid availability on the protein digestibility corrected amino acid score. Proceedings of the Nutrition Week of the International Dairy Federation, Wellington, New Zealand, March 9-11, 1998 1998 ^ Dutch Dairy Foundation on Nutrition and Health Proceedings of the International Workshop on Nutritional Aspects of Milk Proteins in Comparison with Other Proteins, organized by the Dutch Foundation on Nutrition and Health, Utrecht, the Netherlands, March 13-14, 1995 Retrieved from http://en..org/wiki/Biological_value Categories: Proteins | NutritionHidden categories: All articles with statements | Articles with statements since September 2007 | Articles needing more detailed references Views Article Discussion this page History Personal tools Log in / create account Navigation Main page Contents Featured content Current events Random article Search Go Search Interaction Community portal Recent changes Contact Donate to Help Toolbox What links here Related changes Upload file Special pages Printable version Permanent link Cite this page Languages Deutsch Español Italiano Polski Português This page was last modified on 28 August 2008, at 01:24
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