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Brian Turner

Posted on June 21 2018

By Steve Blechman

 Leucine promotes recovery by stimulating the mTOR pathway to increase protein synthesis to repair injured tissue. Leucine is an essential amino acid that serves as a building block for muscle protein synthesis. Leucine is a powerful anabolic trigger— it’s the most potent branched-chain amino acid (BCAA) and a key activator of the mTOR pathway that is critical for muscle protein synthesis that promotes muscle growth.

 Stuart Phillips from McMaster University in Canada, with colleagues, found that a supplement containing 25 grams of whey protein was optimal for stimulating muscle protein synthesis. Consuming less whey slowed protein synthesis. However, consuming low levels of protein (6.25 grams) but adding a leucine supplement caused the same rate of protein synthesis as the 25-gram supplement. Supplements containing 25 grams of whey protein are optimal for stimulating muscle protein synthesis. You can achieve the same result by consuming less whey protein but adding leucine supplements.

 Muscle loss is a serious problem in older adults, leading to decreased quality of life, diabetes and premature death. Dietary protein is an important stimulator of muscle protein synthesis. Older adults can stimulate muscle protein by consuming supplements containing protein and leucine. (Clinical Nutrition 2013, 32: 412-419; Journal of Physiology 2012, 590: 2751-2765)

 Unfortunately, older adults show a blunted muscle protein synthesis (MPS) compared to younger adults. Recent research has suggested that the anabolic resistance can be overcome by consuming greater quantities of leucine. In the most recent study, published in the Journal of Nutrition on June 13, 2018, it is confirmed that leucine and not total protein content of a “…supplement is the primary determinant of muscle protein anabolic responses in healthy older women.” The study showed that “lower protein (10 compared with 25 g/dose) leucine-matched beverage induced similar increases in acute and integrated myoPS in healthy older women. Lower-protein supplements with added leucine may represent an advantageous approach in older adults to maintain skeletal muscle anabolic sensitivity and attenuate muscle loss; however, further work is needed using longer-term interventions.”

 In the March 2018 issue of the International Journal of Sports Nutrition and Exercise Metabolism, it was reported that men fed 6 grams of whey protein supplemented with leucine, isoleucine and valine observed less protein synthesis than whey protein supplemented with just leucine! Also, research has shown that valine can cause insulin resistance in muscle, which is detrimental to muscle growth and enhances the accumulation of body fat.

 Leucine, not branched-chain amino acids (BCAAs), is the most important chemical that turns on the mTOR pathway, so it is likely that consuming leucine after exercise would be more effective (and cheaper) than consuming BCAAs. The addition of isoleucine and valine may hinder the benefits of leucine due to competition for transport into muscle cells. The BCAAs share the same active transport system into cells and muscle cells. Indeed, isoleucine and valine have been shown to inhibit absorption of leucine.

 For best results as an anabolic trigger, take 5 grams of leucine (on an empty stomach) 15-30 minutes before a post-workout meal. By taking pure leucine on an empty stomach, you will get a better spike in blood levels than if you take leucine with food, because food can slow leucine’s absorption. When leucine is taken on an empty stomach, it’s a powerful metabolic switch that turns on protein synthesis. Leucine increases mTOR activity for several hours after training. When leucine is taken after resistance exercise and before a post-workout, protein-containing meal rich in essential amino acids, it triggers greater protein synthesis for improved recovery and greater gains. (Nutrition 2017, 42: 30-36; American Journal of Clinical Nutrition 2016; 104:1594-606; Med Sci Sports Exercise 2011, 43: 2249-2258; Nat Med 2015, 22: 421-426; Biochemical Journal 1996, 100: 7-11; International Journal of Sport Nutrition and Exercise Metabolism, March 2018, 28: 170-177; Amino Acids, June 2008, 35: 147-155; Amino Acids, July 2015, 47: 1389-98)


Leucine, Not Total Protein, Content of a Supplement Is the Primary Determinant of Muscle Protein Anabolic Responses in Healthy Older Women, The Journal of Nutrition, nxy091, June 13, 2018