BCAA – leucine, isoleucine, and valine – are three essential (meaning that body cannot synthesize them by itself) amino acids with branched side chains. Three of them stand for almost 40% of dry muscle mass, so they are an important part of that tissue. Supplementation of leucine, isoleucine, and valine is usually recommended in a 2:1:1 ratio because in this ratio those amino acids appear in muscles.