Branched-Chain Amino Acids
Branched-chain amino acids, including leucine, isoleucine and valine, are used by endurance athletes as an energy source late in exercise when muscle carbohydrate stores are low. Research suggests that BCAA also may delay mental fatigue by altering brain neurotransmitters that contribute to fatigue. The theory is sound, but there is not enough evidence to show that BCAA supplementation can delay fatigue.
Eating foods rich in BCAA is a smart move for athletes, but for reasons other than delaying fatigue. Leucine has been identified as an anabolic trigger to stimulate muscle protein synthesis. Leucine is a key amino acid in whey, a protein in milk. Milk may have a muscle-building advantage over other protein sources because milk protein contains both whey and casein. Whey is a “fast” protein that is rapidly digested and absorbed, leading to a rapid rise in amino acids in the blood, while casein, a “slow” protein, results in a slower release of amino acids. The combined fast and slow release of amino acids leads to a more sustained availability of amino acids to muscles.
Christine Rosenbloom, PhD, RDN, CSSD, is the sports dietitian for Georgia State University athletics and editor-in-chief of Sports Nutrition: A Manual for Professionals, 5th ed. (Academy of Nutrition and Dietetics 2012).