Essential Amino Acid Preserves Muscle Glycogen Maintains Nitrogen Balance Protein Synthesis What is it and where does it come from L-Leucine is an essential branched-chain amino acid BCAA that's broken down in fat structures. The other two essential BCAA's are L-Valine and L-Isoleucine. L-Leucine can not be made by the body, and must be acquired through food or dietary supplements. It can be found in nuts, brown rice and whole wheat bread products. What does L-Leucine do L-Leucine comprises about eight percent of the total amino acid count in your body's protein structures it is the forth most concentrated amino acid in skeletal muscle tissue. As one of the three BCAA's, L-Leucine is essential to your basic health. It has athletic applications. L-Leucine has many beneficial effects on sports performance. It helps preserve lean muscle tissue, it supplies the body with energy when under stress i.e. when engaging in athletic activity, it preserves muscle glycogen glucose stored in muscle