BCAAs are not vitamins, they are amino acids. Amino acids are the building blocks of protein. Each individual amino acid has its own specific function, and the branched-chain amino acids are no different. The BCAAs, leucine, isoleucine, and valine comprise nearly 35 percent of the amino acids making up your skeletal muscle. Each amino acid has its individual functions as well.
Leucine is an essential amino acid, which means that you cannot synthesize it and must consume it via diet, usually from a protein source. Leucine is the only protein that directly contributes to muscle protein synthesis Without this amino acid, your ability to recover from both stress and exercise is compromised. Leucine also contributes to cell growth and the formation of sterols. Sterols are utilized in the process of forming steroidal hormones such as testosterone and estrogen. Eggs, soy and fish are good sources of leucine.
Isoleucine is also an essential amino acid that you cannot produce on your own. Dietary proteins are a source of this amino acid as well, including eggs, seaweed, fish and many seeds. Isoleucine is an important amino acid as it assists your body in the utilization of ketone bodies and fatty acids. This is a critical process of fat mobilization and utilization. A deficit of this amino acid can not only limit your ability to mobilize fat, but cause cerebral dysfunction.
Foods high in valine include eggs, elk, seaweed, soy and watercress. Valine has shown some effect on brain chemistry, which may affect performance, according to a 2001 study published in the "International Journal of Sports Medicine." Valine, like the other branched-chain amino acids, can be broken down and converted to glycogen for use as fuel. This occurs primarily when your carbohydrate stores are low, or your diet is deficient in specific proteins and amino acids.
The BCAAs themselves contribute directly to muscle hypertrophy and recovery. In a 2010 study published in the "International Journal of Sport Nutrition and Exercise Metabolism" it was shown that BCAA supplementation reduced delayed-onset muscle soreness. For endurance athletes, BCAA supplementation has been shown to increase the lactate threshold, or point at which exercise stops using your oxygen systems as a primary source of fuel. A 2009 study in the "Journal of Nutritional Science and Vitaminology" displayed an increase in endurance exercise capacity following BCAA supplementation.