Isoleucine is an essential amino acid, because the body cannot produce it.  Isoleucine helps with glucose uptake and production during exercise.  Isoleucine is known for its ability to induce muscle protein synthesis. It is one of the three amino acids included in BCAA, or the Branched Chain Amino Acids. This makes it widely used in the world of sports and body building for its ability to aid with muscle growth and recovery.