The Biological Value (BV) is a scale of measurement used to determine what percentage of a given nutrient source is utilized by the body. The scale is most frequently applied to protein sources. Biological Value is derived from providing a measure intake of protein, then determining the nitrogen uptake versus nitrogen excretion. The theoretical highest BV of any food source is 100%. In short - BV refers to how well and how quickly your body can actuallyusethe protein you consume.

The BV is particularly used in protein, as the body can not store excess amino acids (other main nutrients, such as fat and carbohydrates can be stored by the body). The daily diet should thus always provide enough protein, and protein of the proper quality, to fulfil the need of the body.

The most limiting amino acid thus determines the BV of the whole protein. If the body needs, for example, 1 gram of phenylalanine daily, and the food supplies 500 gram of protein, but only 0.5 gram of phenylalanine, the BV of the protein is very low. Only a fraction of the protein can be used, the rest has to be excreted.

A low BV can be compensated by consuming other proteins. For example, when a protein is low in leucine, the BV is low. When combining this protein with a protein with high leucine content, the combined BV will be higher than that from the first protein alone. In the combination another amino acid may be limiting, thus determining a new BV. You can never add two biological values to obtain a new biological value. The new value in a combination will be determined by the most restricted amino acid in the combination.

The BV is very important for vegetarians and vegans, who do not consume animal protein. In general, animal proteins have a higher BV than vegetable protein, due to the resemblance of humans and animals. Vegetarians and vegans thus should cleverly select protein sources to obtain a high BV.

Table 1 : Biological value of some foods

Product	Biological value
Whole egg	93.7
Milk	84.5
Fish	76.0
Beef	74.3
Soybeans	72.8
Rice, polished	64.0
Wheat, whole	64.0
Corn	60.0
Beans, dry	58.0

Egg white protein is considered to have one of the best amino acids profiles for human nutrition. Plant proteins generally have lower content of some essential amino acids such as lysine and methionine. Soy protein is one of the best plant proteins, but nevertheless, the most prominent difference is the proportion of the essential sulphur-containing amino acid methionine. Egg white protein has approximately three times more methionine than is found in soy protein.

Amino acid profiles of food proteins

The following table shows representative amino acid profiles of some common foods and dietary protein supplements. The percentages are averages of several commercial products. Casein and whey are milk proteins. Casein is the protein that precipitates from milk when curdled with rennet; it is the basis for making cheese. Whey is the watery part of milk that remains after the casein is separated.

Table 2 : Amino acid composition of food proteins (Percentage (%) by weight of amino acid)

Amino Acid	protein
	egg white	beef	chicken	whey	casein	soy	yeast
alanine	6.6	6.1	5.5	5.2	2.9	4.2	8.3
arginine	5.6	6.5	6.0	2.5	3.7	7.5	6.5
aspartic acid	8.9	9.1	8.9	10.9	6.6	11.5	9.8
cysteine	2.5	1.3	1.3	2.2	0.3	1.3	1.4
glutamic acid	13.5	15.0	15.0	16.8	21.5	19.0	13.5
glycine	3.6	6.1	4.9	2.2	2.1	4.1	4.8
histidine *	2.2	3.2	3.1	2.0	3.0	2.6	2.6
isoleucine *	6.0	4.5	5.3	6.0	5.1	4.8	5.0
leucine *	8.5	8.0	7.5	9.5	9.0	8.1	7.1
lysine *	6.2	8.4	8.5	8.8	3.8	6.2	6.9
methionine *	3.6	2.6	2.8	1.9	2.7	1.3	1.5
phenylalanine *	6.0	3.9	4.0	2.3	5.1	5.2	4.7
proline	3.8	4.8	4.1	6.6	10.7	5.1	4.0
serine	7.3	3.9	3.4	5.4	5.6	5.2	5.1
threonine *	4.4	4.0	4.2	6.9	4.3	3.8	5.8
tryptophan *	1.4	0.7	1.2	2.2	1.3	1.3	1.6
tyrosine	2.7	3.2	3.4	2.7	5.6	3.8	5.0
valine *	7.0	5.0	5.0	6.0	6.6	5.0	6.2

* Essential amino acids