What does high biological value protein and low biological value protein mean? And what is an example food of each?

United Kingdom

The building blocks of protein are amino acids. Each protein has its own specific number and sequence of amino acids. Amino acids can be classified as either essential or non-essential. Non-essential amino acids can be produced in the body from other proteins or carbohydrates. Essential amino acids, however, cannot be produced during metabolism by the body and therefore must be provided by our diet. Eight amino acids (Leucine, Isoleucine, Valine, Threonine, Methionine, Phenylalanine, Tryptophan and Lysine) are considered essential for adults, while nine (those mentioned above plus Histidine) are considered essential for children.

When a protein contains the essential amino acids in a proportion similar to that required by humans, we say that it has high biological value. When one or more essential amino acids are scarce, the protein is said to have low biological value. The amino acid that is in shortest supply in relation to need is termed the limiting amino acid. The limiting amino acid tends to be different in different proteins, so when two foods providing vegetable protein are eaten at a meal, such as a cereal (e.g. bread) and a pulse (e.g. baked beans), the amino acids of one protein may compensate for the limitations of the other, resulting in a combination of higher biological value.

High biological value proteins are provided by animal sources of protein, such as meat, poultry, fish, eggs, milk, cheese and yogurt.

Low biological value proteins are found in plants, legumes, grains, nuts, seeds and vegetables.

For further information see:

and British Nutrition Foundation:
http://www.nutrition.org.uk/home.asp?siteId=43§ionId=607&subSubSectionId=324&subSectionId=320&parentSection=299&which=1