L-leucine is an essential amino acid, meaning you must obtain it through diet because your body can't produce it. You can acquire L-leucine by eating meat, dairy products, eggs, soy and other beans, or by taking it as a supplement. Leucine has potential benefits for weight, lean muscle mass and cholesterol levels, although research is limited and conflicting, according to physician Ray Sahelian, who has a website devoted to natural supplements. Studies have mainly involved animals rather than humans. Consult a qualified health care provider before taking leucine supplements.
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L-leucine, like other essential amino acids, helps maintain muscle mass. For this reason, many bodybuilders and athletes take leucine supplements. One study with animals published in the December 1, 2005 issue of the "Journal of Physiology" found that feeding aged rats leucine inhibited muscle protein breakdown. Another article in the journal discusses this research, explaining that although decreasing dietary fat is advisable for older people, continuing to eat high-quality protein is important.
Weight Loss Benefits
Another animal study, this one appearing in the May 2009 issue of "Medicine & Science in Sports & Exercise," evaluated the effect of L-leucine along with exercise on weight loss in rats who previously ate a high-fat diet for 15 weeks. Researchers divided these rats into two exercise groups, with one group receiving leucine supplementation. Exercise combined with leucine had stronger effects on weight loss than exercise alone.
During the May 2009 "Medicine & Science in Sports & Exercise" study, supplementing the rats with leucine also increased blood levels of high-density lipoprotein cholesterol, the so-called "good" cholesterol. Research published in the June 2007 issue of "Diabetes" investigated the effects on cholesterol levels in mice supplemented with leucine in drinking water. Leucine had no noteworthy metabolic effects on rats eating regular chow. It did produce significant effects on the group eating a high-fat diet compared with other mice eating the same diet without leucine supplementation. Consuming leucine resulted in up to a 32 percent decrease in weight gain and a 25 percent decrease in body fat in these mice, along with improving insulin sensitivity and preventing high blood sugar. The mice receiving leucine also experienced decreased levels of low-density lipoprotein cholesterol, the "bad" cholesterol, of 53 percent and decreased total cholesterol levels of 27 percent.