Strength athletes who use leucine [structural formula shown below] say that they lose fat as a result. Their claims may be founded. According to an animal study done at Columbia University, leucine not only stimulates muscle growth, it also boosts fat burning.
Leucine is a BCAA. In most BCAA supplements, leucine is the most commonly found amino acid. The same is true, but less so, for whey-based protein concentrates. Since it has been known that extra leucine enhances the anabolic response of muscle cells to amino acids, strength athletes have been experimenting with leucine supplements.
The effect of leucine supplementation is sufficient to limit muscle mass breakdown during a period of inactivity. The optimum leucine dose is not yet know, but it may well be on the high side.
Animal tests have shown that leucine supplementation not only stimulates muscle tissue growth, but also the synthesis of collagen [Nutrition. 2004 Feb;20(2):213-7.], so leucine may also help strengthen joints. Epidemiological studies suggest that a high leucine – or BCAA – intake reduces the risk of overweight.
Pretty interesting stuff, leucine. A study published in Diabetes in 2007 makes leucine even more interesting. In this study the researchers did experiments on mice. Half of the animals were given ordinary feed [Chow] and the other half were given feed with extra fat [HFD]. Half of the Chow and HFD mice were given 55 mg extra leucine each day in their drinking water [Leu]. This doubled the leucine intake.
The leucine supplementation was done for 15 weeks. In this period the HFD mice became fatter. But in the HFD mice that got extra leucine the increase in fat mass was a quarter less.
When the researchers monitored the mice’s oxygen expenditure over a day, they saw that the mice on leucine used more oxygen. That means the mice burned more calories, and that’s probably how leucine suppletion inhibited the growth of fat reserves.
An analysis of the muscle and white fat cells from the lab animals showed how this worked: the leucine supplement enhanced the synthesis of the uncoupling protein 3 [UCP3]. UCPs boost the mitochondrias’ burning ability. They ‘decouple’ the burning of food and the production of ATP.
Researchers at Pennsylvania State University who repeated the experiment in 2009 using less leucine reported no effects. [J Nutr. 2009 Apr; 139(4): 715-9.]
Increasing Dietary Leucine Intake Reduces Diet-Induced Obesity and Improves Glucose and Cholesterol Metabolism in Mice via Multimechanisms
Leucine, as an essential amino acid and activator of mTOR (mammalian target of rapamycin), promotes protein synthesis and suppresses protein catabolism. However, the effect of leucine on overall glucose and energy metabolism remains unclear, and whether leucine has beneficial effects as a long-term dietary supplement has not been examined. In the present study, we doubled dietary leucine intake via leucine-containing drinking water in mice with free excess to either a rodent chow or a high-fat diet (HFD). While it produced no major metabolic effects in chow-fed mice, increasing leucine intake resulted in up to 32% reduction of weight gain (P < 0.05) and a 25% decrease in adiposity (P < 0.01) in HFD-fed mice. The reduction of adiposity resulted from increased resting energy expenditure associated with increased expression of uncoupling protein 3 in brown and white adipose tissues and in skeletal muscle, while food intake was not decreased. Increasing leucine intake also prevented HFD-induced hyperglycemia, which was associated with improved insulin sensitivity, decreased plasma concentrations of glucagon and glucogenic amino acids, and downregulation of hepatic glucose-6-phosphatase. Additionally, plasma levels of total and LDL cholesterol were decreased by 27% (P < 0.001) and 53% (P < 0.001), respectively, in leucine supplemented HFD-fed mice compared with the control mice fed the same diet. The reduction in cholesterol levels was largely independent of leucine-induced changes in adiposity. In conclusion, increases in dietary leucine intake substantially decrease diet-induced obesity, hyperglycemia, and hypercholesterolemia in mice with ad libitum consumption of HFD likely via multiple mechanisms. Source: http://diabetes.diabetesjournals.org/