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Leucine: The Great Equalizer

7306-eat9We all love whey protein. In fact, we love it because it tastes great and it’s less filling. Just kidding. But it does taste great, and it also has high levels of leucine, an essential amino acid.

Leucine may be the key that unlocks the anabolic trigger in skeletal muscle. Check out this study published in the American Journal of Clinical Nutrition. Scientists got 40 men to take in various supplement cocktails after doing leg extensions. They got one of the following: 1) 25 grams of whey protein only (W25) [note there is naturally 3 grams of leucine in this], 2) 6.25 grams of whey protein (W6, which has 0.75 grams of leucine), 3) 6.25 grams of whey supplemented with leucine to 3.0 total grams of leu (W6+Low+Leu), 4) 6.25 grams of whey supplemented with high levels of leucine to 5.0 grams (W6+High-Leu), or 5) 6.25 grams of whey supplemented with the BCAAs to 5.0 total grams of leucine (W6+BCAA).

After they consumed these various concoctions, the men’s rates of muscle protein synthesis increased over baseline in every category over 1.5 hours. From hours 1.5 to 4.5 after consumption, protein synthesis remained higher than baseline in all treatments but was the highest in the W25 (267 percent greater) and W6+High-Leu (220 percent greater) conditions. According to the researchers, “A low-protein mixed macronutrient beverage can be as effective as a high-protein dose at stimulating increased muscle-protein-synthesis rates when supplemented with a high amount of leucine.”1

Those results have important implications for formulations of protein beverages designed to enhance muscle anabolism. Here’s more food for thought. First, consuming 25 grams of protein still exerted the greatest anabolic effect. Let’s not forget that. Second, who the heck would use 6.25 grams of whey? Okay, maybe a midget. Seriously, that’s like a tablespoon. Ah, but what if you put 6.25 grams of whey plus five grams of leucine into a shot? Down that shot right after your workout—no need to worry about getting “full” from consuming 25 grams of whey. Then have your normal meal an hour later.

Or how about this? Add five grams of leucine to your soy, casein, rice, hemp or pea protein shake? Perhaps that’ll make it at least as anabolic as whey. Leucine is great for adding muscle protein postexercise, but it’s also great for regenerating skeletal muscle. For instance, in rats that were subjected to a cryolesion—that is, damaging the muscle via cold exposure—scientists found that leucine-supplemented rats regained muscle fiber size and strength better than nonsupplemented muscles.2 So with leucine you get the double whammy: increased muscle fiber size and strength.

—Jose Antonio, Ph.D.


Editor’s note: Jose Antonio, Ph.D., is an assistant professor at Nova Southeastern University in sunny South Florida and the cofounder of the coolest sports nutrition society ever, the ISSN.

1 Churchward-Venne, T.A., et al. (2013). Leucine supplementation of a low-protein mixed-macronutrient beverage enhances myofibrillar protein synthesis in young men: a double-blind, randomized trial. Am J Clin Nutr. Published online November 27.

2 Pereira, M.G., et al. (2014). Leucine supplementation improves skeletal muscle regeneration after cryolesion in rats. PLoS ONE. 9(1):e85283.

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