Keep the Muscle and Lose the Fat with Leucine
by: Robbie Durand
Leucine has been reported to have unique effects on stimulating protein synthesis compared to other amino acids. Leucine is not just a supplement for the off-season bodybuilder, but may be even more important to use while dieting. During catabolic periods, such as fasting or energy restriction, supplementation with leucine or a complete mixture of the three BCAAs leucine, isoleucine, and valine stimulates muscle protein synthesis. Likewise, leucine supplementation stimulates recovery of muscle protein synthesis after exercise.
In this month’s Journal of Amino Acids, researchers put together a comprehensive review article titled, “Leucine nutrition in animals and nutrition: mTOR signaling and beyond.” The article described the many benefits of leucine supplementation, which are beneficial to the dieting bodybuilder. Leucine is not only a substrate for protein synthesis of skeletal muscle, but also plays more roles beyond that. Leucine activates signaling factor of mTOR to promote protein synthesis in skeletal muscle and in adipose tissue. It is also a major regulator of the mTOR-signaling pathway. Additionally, leucine regulates blood glucose level by promoting gluconeogenesis and aids in the retention of lean mass in a hypocaloric state. Here is a brief summary of four findings reported in the review paper:
- Leucine directly stimulates mTOR in the hypothalamus resulting in decreased food intake and weight gain. Except for leucine, no other amino acid is observed to regulate mTOR signaling in the hypothalamus (i.e. area of the brain regulating appetite). Stimulation of mTOR decreases appetite, which may be the reason high protein diets enhance weight loss by reducing appetite.
- Leucine affects satiety by stimulating of leptin secretion (Leptin is a regulator of appetite). Low leptin levels result in increased hunger. Leptin is regulated by mTOR which leucine is known to stimulate the mTOR pathway, which may result in reduced appetite. Interesting, leptin secretion is decreased and hunger increases when the mTOR blocking drug rapamycin is administered demonstrating the leptin secretion is regulated my mTOR.
- Leucine regulates energy metabolism by increasing the number of mitochondria. More mitochondria means more fat burning in muscle cells. Brown fat is rich in mitochondria, which is why it is a potent fat burner. Leucine enhances mitochondrial number and gene expression in both muscle and adipocytes, where leucine also stimulates oxygen consumption. This suggests that leucine enhances metabolic rate. It also provides further evidence to support the effects of leucine in enhancing energy utilization.
- Leucine and BCAA’s have been shown to decrease fat mass, bodyweight and improve glucose metabolism. During low calorie diet period, leucine supplementation serves to promote gluconeogenesis (i.e. creation of glucose from amino acids/fatty acids) to maintain blood glucose level when dietary glucose is restricted but protein is plentiful. Leucine also displays an anabolic action in terms of protein metabolism and favorably affects body composition in catabolic situations. Long term of L-leucine administration on rats for 6 weeks in a catabolic situation caused by food restriction (50%) increases body fat loss (25%) and improves liver protein status. In addition, leucine with other BCAA administered to wrestlers for 19 days of caloric restriction shows reduction of body fat than caloric restriction conducted alone. This suggests an effect of nutrient partitioning induced by an increased ingestion of leucine by enhancing fat loss.
Two weight loss trials using diets designed to provide 10 g/d of leucine (∼125 grams/day of dietary protein) with a minimum of 2.5 g of leucine at each of three meals . At the end of the study, comparisons with subjects following the USDA Food Guide Pyramid, subjects consuming the protein-rich diets lost more weight and were more effective in correcting body composition during weight loss. Consumption of the protein-rich diet resulted in greater loss of body fat and attenuated loss of lean tissue consistent with a protein sparing mechanism for leucine.Leucine may be a useful diet tool for the bodybuilder or athlete who is looking to lose weight while maintaining muscle mass.
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