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I Love Leucine- Most Potent BCAA: the Anabolic Trigger

Brian Turner

Posted on April 27 2018

By Steve Blechman and Tom Fahey, Ed.D.


 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. Testosterone acts through the mTOR pathway to promote muscle protein synthesis. Leucine has many benefits: powering muscle growth, preventing muscle loss, increasing insulin sensitivity, enhancing fat metabolism and enhancing recovery.

 Increases Muscle Protein Synthesis. Muscles increase in size when muscle protein synthesis is greater than muscle breakdown. Protein balance is influenced by muscle tension, physical activity, calories, protein and amino acids. High protein intake temporarily increases protein synthesis in the muscles by activating key biochemical pathways in the cells. When combined with protein, leucine triggers protein synthesis for greater gains.

 A study from Maastricht University Medical Center in the Netherlands found that supplementing 20 grams of casein protein and 2.5 grams of crystalline leucine increased protein synthesis in older men 20 percent greater than protein alone. Researchers used sophisticated chemical tracers to measure protein synthesis.

 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 several times per day, containing 20 to 30 grams of protein. (Clinical Nutrition 2013, 32: 412-419; Journal of Physiology 2012, 590: 2751-2765)

 Increases Insulin Sensitivity. Long-term leucine supplementation increased insulin sensitivity and lean bodyweight, according to a Chinese study on rats. They gave rats high doses of leucine for 24 weeks. The scientists speculated that leucine worked by reducing oxidative stress and improving insulin signaling. Leucine is the real deal when it comes to muscle-promoting supplements, particularly in older adults. (Molecular Nutrition & Food Research 2013, 57: 1067-1079)

 Enhances Fat Metabolism. Leucine builds proteins and chemically signals key metabolic pathways. Higher dietary intake of leucine is linked to a reduced risk of obesity. Researchers from Suzhou University in China, in a study on mice fed a high-fat diet, found that long-term leucine supplementation enhanced fat metabolism, prevented fat and weight gain, reduced fat accumulation in the liver and increased brown fat activity.

 Leucine activates the mTOR pathway, which is important for muscle protein synthesis. It stimulates brown fat, which helps regulate bodyweight by converting food energy to heat instead of storing it as fat. Leucine is an important supplement for building lean body mass. Whey protein is high in leucine, but athletes benefit from additional leucine supplements (about 3-5 grams). (Food & Nutrition Research, published online September 9, 2016)

 Prevents Muscle Wasting. Muscle atrophy (muscle loss) is a serious problem in older adults and bedridden patients. Muscle is critical for quality of life. Muscle loss reduces the ability to move, and promotes painful joints. Muscle is the largest tissue in the body and is critical for metabolic health. Muscle loss reduces the capacity to control blood sugar and other fuels and makes it more difficult to control blood pressure, blood fats and fat deposition.

 Leucine supplements are a simple, effective way to reduce muscle loss in bedridden patients and older adults. A series of studies from the University of Texas Medical Branch in Galveston found that feeding leucine mixed in a cocktail of essential amino acids and carbohydrates reduced muscle loss by half during 28 days of bed rest. Bedridden people usually have reduced appetites, which promote muscle loss. Feeding 3-5 grams of leucine is an easy way to promote muscle protein synthesis and prevent muscle breakdown. (Nutra, published online August 26, 2013)

 Prevents Muscle Loss During Bed Rest. Too much bed rest will kill you! In 1947, British physician Richard Asher wrote, “Teach us to live that we may dread unnecessary time in bed. Get people up and we may save our patients from an early grave.” Bed rest studies by scientists from NASA showed that three weeks of total bed rest (not allowed to get out of bed during the experiment) caused a 25 percent decrease in aerobic capacity, a 13 percent decrease in muscle mass and a 25 to 35 percent decrease in strength and power.

 Everyone gets sick occasionally, so how do you maintain precious training gains when you have to stay in bed? A study led by Kirk English from the University of Texas Medical Branch in Galveston, Texas found that supplementing the amino acid leucine with every meal (0.06 grams per kilogram of bodyweight) during 14 days of bed rest prevented some changes in muscle mass, strength, power and body fat, compared to a placebo (fake leucine). Leucine is an amino acid that acts as a chemical signal to turn on protein synthesis in the muscle cells. Leucine can prevent physical deterioration during short breaks in training or when you are confined to bed with the flu. (American Journal Clinical Nutrition 2016, 103: 465-473)

 BCAAs or Leucine Best Taken After Exercise. Leucine, isoleucine and valine are called branched-chain amino acids (BCAAs). They are essential amino acids, which means they must be consumed in the diet. BCAAs are involved in protein synthesis, tissue repair, signaling a biochemical pathway essential for muscle protein synthesis (i.e., mTOR) and blood sugar control. A meta-analysis that combined the results of seven studies showed that BCAA supplements are best taken after exercise, not before or during exercise (intra-workout). The studies revealed that BCAAs taken during exercise are “not effective on muscle soreness at follow-up time,” the researchers wrote.

 Leucine consumption before your workout promotes sluggishness and fatigue. Recent research has shown that leucine competitively inhibits dopamine precursor tyrosine into the brain, and reduces dopamine levels. Dopamine and noradrenaline are the “flight-or-fight” hormones that allow the body to perform at higher levels than normal. Increasing dopamine reduces fatigue and increases mental arousal, focus, confidence and greater levels of motivation. Pre-workout leucine and BCAA consumption is not the best for optimal muscular performance.

 According to the meta-analysis, when BCAAs are taken after exercise, they reduce post-exercise muscle soreness and creatine kinase— a marker of muscle damage— better than rest alone.

 BCAAs promote recovery by stimulating the mTOR pathway to increase protein synthesis to repair injured tissue. Leucine, one of the 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 leucine. 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.

 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)


AML's PostWorkout has 5g Leucine.