BCAA is an amino acid having aliphatic side-chains with a branch (a carbon atom bound to more than two other carbon atoms). Among the proteinogenic amino acids, there are three BCAAs: leucine, isoleucine and valine.

Branched Amino Acid/BCAA are known as the stress amino acids. Thirty percent of the diet should be proteins when the body is under severe stress, because stress causes protein to break down faster. BCAAs have regulatory effects on overall protein metabolism and are required in larger amounts during stress than are other amino acids (and probably proportionately more leucine than either valine or isoleucine).Furthermore, when given as supplements, BCAAs decrease the rate of breakdown and utilisation of other amino acids and stimulate protein synthesis. Therefore these BCAAs are useful in conditions of stress caused by trauma, surgery, liver failure, infection,fever, starvation, muscle training and weight lifting. BCAAs are unique in that skeletal muscles can use them directly as an energy source.