The branched-chain amino acids (BCAAs) are leucine, isoleucine, and valine. They make up 35% of your muscle mass. Besides building cells and repairing tissue, they form antibodies, they are part of the enzyme and hormonal system, they build RNA and DNA and they carry oxygen throughout the body and regulate blood sugar level. BCAAs are considered essential amino acids because human beings cannot survive unless these amino acids are present in the diet.
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The branched-chain amino acids (BCAAs) are leucine, isoleucine, and valine. They make up 35% of your muscle mass. Besides building cells and repairing tissue, they form antibodies, they are part of the enzyme and hormonal system, they build RNA and DNA and they carry oxygen throughout the body and regulate blood sugar level. BCAAs are considered essential amino acids because human beings cannot survive unless these amino acids are present in the diet.
During intense weight training the body is in a highly catabolic condition. At this time glycogen stores are being rapidly depleted and the liver in turn must synthesize glucose by a conversion of L-Alanine via the glucose-alanine cycle. The BCAA's are involved in maintaining glucose homeostasis through the glucose-alanine cycle. The glucose-alanine cycle involves pyruvate (derived from glucose) being transaminated in muscle to form alanine, with the BCAA serving as the main nitrogen source (donors) for the synthesis of alanine. Then the liver can synthesize glucose by a conversion of L-Alanine.
The BCAA's are special because they aren't significantly broken down in the liver and this results in release of the BCAA's from the liver into circulation. The BCAA are different from the other 17 amino acids in that they are primarily metabolized in skeletal muscle and metabolized at a much lower rate in the liver. The rate limiting enzyme in BCAA catabolism is Branched Chain Keto Acid Dehydrogenase, which is much more active in skeletal muscle than in the liver. Skeletal muscles are able to break down the BCAA's for energy and will do so during increased energy needs such as starvation, trauma, or exercise.
The BCAA's stimulate protein synthesis through insulin secretion/activation of the PI3K pathway, and through activation of mTOR.
One pathway through which protein synthesis can be increased is the phosphatodyl-inositol-3-kinase pathway (PI3K). PI3K regulates glucose uptake through GLUT4 translocation and also increases amino acid uptake. Insulin, the body's "storage" hormone, works by activating the PI3K pathway.
Interestingly, leucine ingestion causes insulin secretion, but leucine can also directly activate PI3K in the absence insulin. So not only can leucine increase glucose uptake, it can also increase it's own and other amino acids' uptake into cells.
The Mammalian Target of Rapamycin (mTOR) is one of the body's protein synthesis regulators. When mTOR is activated (high ATP levels sensed) protein synthesis is increased and when mTOR is suppressed (low ATP levels are sensed) protein synthesis is blunted. Leucine is the key regulator of the mTOR-signaling pathway.
Intake of leucine stimulates expression of the hormone leptin in adipocytes. Leptin is a hormone, which is involved in the regulation of metabolism, body weight, and appetite.
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Amino acids 
