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Leucine is one of more than a dozen amino acids needed to synthesize proteins and build muscle in our body.  Researchers have known about leucine for decades, but exciting new research has shed a new and broader light on this important health-promoting amino acid. Much of protein's benefits
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may be attributable specifically to leucine due to its ability to stimulate protein synthesis, help turn on the body's switch to build muscle, and spare muscle when dieting. A series of cellular studies has now clearly shown that leucine directly activates a critical compound in muscle called the mTOR. It turns out mTOR is like a molecular switch that turns on the protein synthetic machinery in muscle, and leucine is one of the major activators of mTOR. Thus, leucine not only provides the building blocks for protein synthesis, it also has a critical role in up-regulating the process.  A new study examined the effects of high dose leucine supplementation around a high-intensity resistance exercise workout. Subject consumed about 19 grams leucine before and after exercise and then were tested daily for 4 days after exercise to study recovery. Isometric peak squat force output was significantly decreased over the four days recovery in the control group. There was less of a drop in force output with leucine supplementation. The better maintenance of force production with leucine supplementation is consistent with other work showing less loss of muscle strength with lower doses of leucine. This study used a very large dose of leucine, probably impractical in most settings, but nonetheless does contribute to a growing body of evidence indicates that increasing leucine intake can have multiple benefits.
  . Kirby TJ, Triplett NT, Haines TL, Skinner JW, Fairbrother KR, McBride JM. Effect of leucine supplementation on indices of muscle damage following drop jumps and resistance exercise. Amino Acids. 2011 May 12.