The branched-chain amino acids (BCAA’s) leucine, isoleucine, and valine are used by the body to manufacture proteins. Muscles have a high content of BCAA’s. Adequate amounts of BCAA’s are usually obtained from the diet; however, injury can increase the body’s need for BCAA’s in order to repair damage. BCAA’s are found in all protein-containing foods, but the best sources are red meat and dairy products.

BCAA’s are often used for their muscle-building properties; however, the majority of evidence obtained from clinical studies suggests that they do not improve performance, reduce fatigue, or increase the body’s muscle/fat ratio. Results of a 1999 study suggest that BCAA’s might improve the symptoms of tardive dyskinesia, a movement disorder caused by long-term use of antipsychotic drugs. Other studies have found that supplementary BCAA’s may reduce the symptoms of Lou Gehrig’s disease (amyotrophic lateral sclerosis (ALS)), and improve the appetite of cancer patients.

The therapeutic dose is 1-5 g per day, depending upon requirements.

The maximum safe level has not been established. When taken in excess BCAA’s are simply converted into other amino acids, thus they are generally regarded as safe, even in large doses.

People with kidney or liver disease should consult their doctor before taking supplementary leucine, isoleucine, or valine. BCAA’s can reduce the effectiveness of anti-Parkinson’s drugs, for example levodopa.