Leucine
Jose Antonio, Ph.D.

The dynamic triplet of amino acids, aka the branched-chain amino acids, include valine, isoleucine, and leucine. Of the three, leucine is clearly the ‘star of the show!’ Leucine, as an essential amino acid and activator of mTOR (an important regulator of cell growth), promotes protein synthesis and suppresses protein catabolism. In addition, there’s some new information showing that leucine affects overall glucose and energy metabolism. Recently, scientists doubled dietary leucine intake via leucine-containing drinking water in mice with free excess to either a typical ‘mouse’ 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 and a 25% decrease in adiposity in HFD-fed mice. The reduction of adiposity resulted in part from an increased resting energy expenditure; also, increasing leucine intake also prevented HFD-induced hyperglycemia, which was associated with improved insulin sensitivity. In conclusion, the authors concluded that “increases in dietary leucine intake substantially decrease diet-induced obesity, hyperglycemia, and hypercholesterolemia in mice with ad lib consumption of HFD likely via multiple mechanisms.” 1 Pretty nifty, eh? Well, on top of that, there is human data showing an ergogenic (i.e. performance-enhancing) effect of leucine. Thirteen (ten female, three male) competitive outrigger canoeists underwent testing before and after 6-week supplementation with either capsulated L-leucine (45 mg/kg.d) [that’s equal to 3.15 grams of leucine for a 154 lb individual] or placebo (corn flour). Testing included anthropometry, 10 second upper body power and work and a row to exhaustion at 70-75% maximal aerobic power where perceived exertion (RPE), heart rate 2 and plasma BCAA and tryptophan concentrations were assessed. What happened? Leucine supplementation resulted in significant increases in plasma leucine and total BCAA concentrations. Upper body power and work significantly increased in both groups after supplementation but power was significantly greater after leucine supplementation compared to the placebo. Rowing time significantly increased and average RPE significantly decreased with leucine supplementation while these variables were unchanged with the placebo. Leucine supplementation had no effect on the plasma tryptophan to BCAA ratio, HR or anthropometric variables. Six weeks' dietary leucine supplementation significantly improved endurance performance and upper body power in outrigger canoeists.3 As a very amateur outrigger canoeist myself, I can testify to the benefits of leucine.
So next time you drink your protein shake, throw a bit of leucine in it. A dose in the 1-3 gram range would be effective.
References
1. Zhang Y, Guo K, Leblanc RE, Loh D, Schwartz GJ, Yu YH: Increasing dietary leucine intake reduces diet-induced obesity and improves glucose and cholesterol metabolism in mice via multi-mechanisms. Diabetes 2007
2. McDowell HE, Christie GR, Stenhouse G, Hundal HS: Leucine activates system A amino acid transport in L6 rat skeletal muscle cells. Am J Physiol 1995, 269:C1287-1294
3. Crowe MJ, Weatherson JN, Bowden BF: Effects of dietary leucine supplementation on exercise performance. Eur J Appl Physiol 2005:1-9

 

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