Leucine is an amino acid, part of the branched-chain amino acids along with isoleucine and valine. It may lower elevated blood sugar levels and aid in increasing growth hormone production. As part of BCAA it protects muscle, acts as fuel, and promotes healing of bone, skin, and muscle tissue. It can be found singly, as part of an amino acid complex, or a sports supplement. It is found in brown rice, meat, nuts, and whole wheat. Leucine must be taken in moderation and with isoleucine and valine.