Branched-chain amino acids (BCAAs) are naturally occurring molecules (leucine, isoleucine, and valine) that the body uses to build proteins. The term "branched chain" refers to the molecular structure of these particular amino acids. Muscles have a particularly high content of BCAAs.

For reasons that are not entirely clear, BCAA supplements may improve appetite in cancer patients and slow the progression of amyotrophic lateral sclerosis (ALS, or Lou Gehrig's disease, a terrible condition that leads to degeneration of nerves, atrophy of the muscles, and eventual death).

BCAAs have also been proposed as a supplement to boost athletic performance.

Dietary protein usually provides all the BCAAs you need. However, physical stress and injury can increase your need for BCAAs to repair damage, so supplementation may be helpful.

BCAAs are present in all protein-containing foods, but the best sources are red meat and dairy products. Chicken, fish, and eggs are excellent sources as well. Whey protein and egg protein supplements are another way to ensure you're getting enough BCAAs. Supplements may contain all three BCAAs together or simply individual BCAAs.