PUMPED
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Three major properties of a protein source affect its BV:
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 affect the 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 inyeast extract) to prevent this.
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.
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
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.
Common foodstuffs and their values: (Note: this scale uses 100 as 100% of the nitrogen incorporated.)
- Amino acid composition, and the limiting amino acid, which is usually lysine
- Preparation (cooking)
- Vitamin and mineral content
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 affect the 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 inyeast extract) to prevent this.
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.
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
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.
Common foodstuffs and their values: (Note: this scale uses 100 as 100% of the nitrogen incorporated.)
- Whey Protein: 96 [SUP][11][/SUP]
- Whole Soy Bean: 96 [SUP][12][/SUP]
- Human milk: 95[SUP][13][/SUP]
- Chicken egg: 94[SUP][13][/SUP]
- Soybean milk: 91[SUP][12][/SUP]
- Buckwheat: 90+[SUP][14][/SUP]
- Cow milk: 90[SUP][13][/SUP]
- Cheese: 84[SUP][15][/SUP]
- Quinoa: 83[SUP][16][/SUP]
- Rice: 83[SUP][15][/SUP]
- Defatted soy flour: 81[SUP][12][/SUP]
- Fish: 76[SUP][17][/SUP]
- Beef: 74.3[SUP][17][/SUP]
- Immature bean: 65[SUP][12][/SUP]
- Full-fat soy flour: 64[SUP][12][/SUP]
- Soybean curd (tofu): 64[SUP][12][/SUP]
- Whole wheat: 64[SUP][17][/SUP]
- White flour: 41[SUP][12][/SUP]
- Whey protein concentrate: 104
- Whole egg: 100
- Cow milk: 91
- Beef: 80
- Casein: 77
- Soy: 74
- Wheat gluten: 64
