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 captures how readily the digested protein can be used in protein synthesis in the cells of the organism. Proteins are the major source of nitrogen in food. BV assumes protein is the only source of nitrogen and measures the amount of nitrogen ingested in relation to the amount which is subsequently 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 uses two similar scales:
The 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 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 ascertain reliable figures.
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.[2][3]