A branched-chain amino acid (BCAA) is an amino acid having aliphatic side-chains with a branch (a central carbon atom bound to three or more carbon atoms).Among the proteinogenic amino acids, there are three BCAAs: leucine, isoleucine and valine. Non-proteinogenic BCAAs include norvaline and 2-aminoisobutyric acid. branched-chain amino acid (BCAA) is an amino acid having aliphatic side-chains with a branch (a central carbon atom bound to three or more carbon atoms).