PURE LEUCINE INCREASES MUSCLE GROWTH FACTOR (IGF-1): The Key Anabolic Trigger!
By Steve Blechman
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) of the mTOR pathway that is critical for muscle protein synthesis that promotes muscle growth. Leucine has many growth benefits: preventing muscle loss, increasing insulin sensitivity, enhancing fat metabolism and enhancing recovery.
A randomized controlled study published in the Journal of the American College of Nutrition found that taking 3 grams of pure leucine after resistance training exercise increased muscle insulin-like growth factor 1 (IGF-1). IGF-1 is a potent anabolic hormone derived from growth hormone. Increased IGF-1 in muscle can increase muscle protein synthesis and muscle growth. IGF-1 also increases lean body mass and enhances tissue repair and accelerates recovery. What’s most significant of this randomized trial was the acute increase of IGF-1, not only in blood, but significantly, two hours and six hours post resistance training exercise in muscle after a single dose of 3 grams of leucine but not the placebo! Increasing igf-1 in muscle is key for stimulating muscle protein synthesis. In this study, “Nine resistance-trained men performed 3 lower-body resistance exercise sessions involving 4 sets of 8-10 repetitions at 75%-80% one repetition maximum (1-RM) on the angled leg press and knee extension exercises. Immediately following each session, participants orally ingested 3 g cellulose placebo (PLC), l-leucine (LEU), or ursolic acid (UA). Blood samples were obtained pre-exercise and at 0.5, 2, and 6 hours postexercise. Muscle biopsies were obtained pre-exercise and at 2 and 6 hours postexercise.”
The conclusion of this study was, “Three grams of l-leucine and ursolic acid had no effect on Akt/mTORC1 signaling or serum insulin or IGF-1; however, l-leucine increased skeletal muscle IGF-1 concentration in resistance-trained men.”
Leucine, not branched-chain amino acids, 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.
Robert R. Wolfe, noted amino acid researcher, said in the Journal of the International Society of Sports Nutrition (2017) that “BCAAs also compete with other amino acids for transport, including phenylalanine, and this competition could affect the intramuscular availability of other EAAs. As a result of competition for transporters, it is possible that leucine alone, for example, could have a transitory stimulatory effect on muscle protein synthesis where the BCAAs fail to elicit such response.”
Studies indicate increases in muscle protein synthesis are dependent on leucine concentration! Leucine stimulates the anabolic effects of muscle protein by itself. A Japanese study published on October 18, 2018 in the journal Nutrients found that taking leucine supplements alone may be better for muscle protein synthesis and more anabolic than leucine from food! Japanese researchers found that blood levels of leucine were higher from pure, free leucine taken alone compared to the same amount of leucine in a meal. Increase in muscle protein synthesis is dependent on leucine concentration. Research has shown that leucine stimulates the anabolic effect of muscle protein on its own (Wilkinson et al., J Physiol, 2013). The Nutrients study showed that, “based on these findings, it is presumed that compared to the intake of protein alone or free amino acids alone, the intake of dietary protein from mixed meals may result in a lower maximum plasma leucine concentration. However, no study to date has investigated the changes in amino acid concentrations after the ingestion of mixed meals in comparison to those after the intake of a similar amount of free amino acids.”
In a randomized crossover study, 10 healthy, young Japanese men underwent tests under different conditions: consuming 2 grams of leucine alone; a mixed meal with 2.15 grams of leucine without any additional leucine supplementation; 2 grams of leucine right after a meal; and the final serving consisted of 2 grams of leucine, 180 minutes after a meal.
The study concluded that “based on the aforementioned discussions, the intake of free leucine alone markedly increased the plasma leucine concentration. However, the increase in leucine concentration after the intake of a mixed meal containing the same amount of leucine was significantly less than that of free leucine intake alone. Moreover, when free leucine was ingested after a mixed meal with the purpose of increasing the plasma leucine concentration, the maximum plasma concentration was attenuated when it was ingested immediately after the mixed meal, despite the fact that the total leucine content was doubled. These results suggest that when free amino acids ingested with the purpose of increasing plasma amino acid concentrations, the timing in relation to the mixed meal intake needs to be considered.”
For best results to use as an anabolic trigger, take 5 grams of leucine (on an empty stomach) 30 minutes before a post-workout meal, or protein shake. A meta-analysis (Nutrition, 2017) that combined the results of seven studies showed that BCAA supplements are best taken after exercise, not before or during exercise (intra-workout.) (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).
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. The addition of isoleucine and valine may hinder the benefits of leucine due to competition for transport into muscle cells. 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.
THE BEST LEUCINE SUPPLEMENT
AML Post Workout contains 5 grams of pure leucine. It also contains 5 grams of creatine monohydrate and 2.5 grams of betaine. Creatine has been reported in the scientific literature to function as a myostatin inhibitor supporting muscle growth. Betaine has also been found in the scientific research to stimulate growth hormone (GH) and insulin-like-growth-factor-1 (IGF-1). Combining 5 grams of pure leucine along with 5 grams of creatine monohydrate and 2.5 grams of betaine makes AML Post Workout a potent, muscle growth and recovery supplement. For best results we suggest taking one serving of AML Post Workout by itself (on an empty stomach) 15-30 minutes before a post-workout meal, providing all the essential amino acids required for muscle protein synthesis.
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