Branched-chain amino acids are essential nutrients that the body obtains from proteins found in food, especially meat, dairy products, and legumes. They include leucine, isoleucine, and valine. “Branched-chain” refers to the chemical structure of these amino acids. People use branched-chain amino acids for medicine. Branched-chain amino acids to prevent fatigue and improve concentration. Many athletes use branched-chain amino acids to improve performance and reduce protein and muscle breakdown during intense exercise. Branched-chain amino acids stimulate the building of protein in muscle and possibly reduce muscle breakdown.