High Quality Content by WIKIPEDIA articles! 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 summarises how readily the broken down protein can be used in protein synthesis in the cells of the organism. Proteins are the major source of nitrogen in food, unlike carbohydrates and fats. This method assumes protein is the only source of nitrogen and measures the proportion of this nitrogen absorbed by the body which is then 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.