L-Leucine

The Master Anabolic Trigger and More!
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There are many stresses in life that threaten our ability to hang on to our hard-earned muscle. One obvious threat is illness. It doesn’t have to be life threatening to rob you of muscle mass. It can be something as common as a 24-hour stomach virus. Take, for example, my own experience this past summer. I got a bug, and before I knew it, I had lost 12 pounds in two days. Yeah, most of it came back pretty quickly...but not all of it. Fasting or even just dieting also eats away at our gains. But there is one kind of stress that not many people know about that eats up muscle like almost nothing else: climbing at altitude.

That’s right, few people are aware, save those who do it, that climbing
at altitude wreaks havoc on muscle mass. So what can we do about all these catabolic threats? You might be surprised to hear that something as simple as leucine, an amino acid that belongs to the group called branched chain amino acids (BCAAs), can have a big impact on how much you and how much you lose when faced with one of these challenges.

One person who is well aware of the catabolic effects of climbing at altitude is Stacie Wing-Gaia, Ph.D. She also happens to be a colleague of mine at the University of Utah. She has recently completed research on Mount Everest, exploring the effects of leucine supplementation on the ability of climbers to keep muscle mass at altitude. One thing that’s different about climbing at altitude compared with normal strenuous climbing is the inordinate amount of weight that is lost as muscle. In addition to the difficulty of meeting the caloric requirements of climbing, there may be other mechanisms involved due to the limited oxygen at altitude.

In her study, climbers were provided specially prepared food bars that contained the additional leucine. They were instructed to eat a bar three times per day. Measures of body composition were taken at the beginning and after their climb, which lasted several days. The data are still being analyzed, but there is evidence that leucine might be able to preserve lean mass and facilitate fat burning under such stressful conditions. I’m sure we’ll hear more about this research in the future.

The essential amino acid L-leucine is one of three BCAAs, along with isoleucine and valine. Of the three, leucine has become a star because of its potent anabolic properties in muscle tissue. Many of the effects of leucine are associated with the activation of mammalian target of rapamycin (mTOR) transduction pathway in muscle cells. This pathway is well known to be associated with anabolic signaling within muscle. In addition, leucine appears to have mTOR-independent anabolic effects as well.(1) But it gets even better. Not only does leucine directly trigger muscle protein synthesis, it also inhibits protein breakdown (i.e., it’s anticatabolic). Studies of leucine supplementation clearly show that it can inhibit skeletal muscle breakdown.(2) It should be clear why Dr. Wing-Gaia chose supplemental leucine to try to combat muscle loss at altitude.

Body fat may also be favorably affected by leucine supplementation. Infusion of leucine leads to an increase in thermogenesis, and at least one study in rats shows that leucine enhances fat loss and preserves muscle tissue during food restriction.(3,4) In vitro it’s been shown that in fat cells exposed to leucine, genes that are needed to create fat are suppressed. In muscle cells leucine exposure increases their ability to burn fat for fuel.(5) The ability of leucine to increase protein synthesis in muscle tissue, decrease fat storage, and increase fat burning makes leucine a true energy-partitioning supplement.

Finally there is a question of dose. From all the talk it would seem as if I’m hollering, “Feels like Deca!” Hopefully you know me better than to think I would pull that one on anybody. It is true; leucine is a bona fide anabolic nutrient signal in muscle tissue. Muscle tissue however has limits in the extent to which it can increase protein synthesis.(6,7) For the average guy, it appears that as little as 2 grams is enough to maximize the anabolic effect, assuming you are ingesting sufficient essential amino acids with it. After all, the muscle cannot synthesize new muscle proteins out of just leucine. The anabolic effect of leucine is dependent on the availability of essential amino acids. As you might have guessed by now, one of the most accessible sources of leucine combined with all essential amino acids is whey protein. Twenty-five grams of whey protein provide 3 grams of leucine, which just happens to be the right 
amount to maximally stimulate protein synthesis. When dieting, however, I 
would recommend that you supplement with additional leucine in your protein drinks. Although supplying more than
3 grams of leucine is all you need to maximally stimulate protein synthesis,
 more leucine does impart additional anticatabolic affects.(2)

 

References: 1. M.H. Stipanuk, Nutr. Rev., 2007, 65, 122–129; 2. N.E. Zanchi et al., Nutr Metab., 2008, 5, 20; 3. L. Tappy, Am J Clin Nutr., 1993, 57, 912–916; 4. J. Donato Jr., Nutri., 2006, 22(5):520–27; 5. X. Sun and M. Zemel, Lipids, 2007, 42(4):297–305; 6. D. Cuthbertson et al., FASEB J., 2005, 19, 422–24; 7. D.R. Moore et al., Am J Clin Nutr., 2009, 89(1):161–68

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