The biological value of the proteins of a foodstuff is a measure of the efficiency with which these dietary proteins can be converted into the body’s own proteins. The more similar the dietary proteins are to the body proteins in their amino acid composition, the fewer dietary proteins are required for their composition (protein balance = 0, protein synthesis = protein degradation). The content of essential amino acids is of particular importance here. The reference value is whole egg, whose biological value was defined as 100 or 1 (100 %), since it was the protein source with the highest known biological value at the time the definition was made.

The concept of biological valence was developed by the German nutritionist Karl Thomas (1883-1969) at the suggestion of Max Rubner.