science nutrition blog

By Steve Blechman

The amino acid leucine plays a pivotal role in promoting recovery by stimulating the mTOR pathway, which increases muscle protein synthesis to repair injured tissue. As an essential amino acid, leucine serves as a critical building block for muscle protein synthesis. It is recognized as a powerful anabolic trigger and is the most potent branched-chain amino acid (BCAA), acting as a key activator of the mTOR pathway essential for leucine protein synthesis that promotes muscle growth.

Research conducted by Stuart Phillips and colleagues from McMaster University in Canada highlights the importance of leucine supplementation. They discovered that a supplement containing 25 grams of whey protein is optimal for stimulating muscle protein synthesis. However, consuming lower amounts of whey protein (6.25 grams) in conjunction with leucine supplementation achieved the same rate of protein synthesis as the 25-gram supplement. This finding underscores the benefits of leucine in muscle recovery, amino acid and muscle growth.

Muscle loss is a significant concern for older adults, leading to decreased quality of life, increased risk of diabetes, and premature death. Dietary protein is a crucial stimulator of muscle protein synthesis, and older adults can enhance muscle protein synthesis by consuming supplements rich in protein and leucine, emphasizing the benefits of essential amino acids. (Clinical Nutrition 2013, 32: 412-419; Journal of Physiology 2012, 590: 2751-2765)

Unfortunately, older adults exhibit a blunted muscle protein synthesis response compared to younger individuals. Recent studies suggest that this anabolic resistance can be overcome by increasing leucine intake. A study published in the Journal of Nutrition on June 13, 2018, confirmed that leucine, rather than the total protein content of a supplement, is the primary determinant of muscle protein anabolic responses in healthy older women. The study demonstrated that a lower-protein, leucine-matched beverage induced similar increases in acute and integrated muscle protein synthesis in healthy older women. Lower-protein supplements with added leucine may offer an advantageous approach for older adults to maintain skeletal muscle anabolic sensitivity and mitigate muscle loss, although further research is needed for long-term interventions.

The March 2018 issue of the International Journal of Sports Nutrition and Exercise Metabolism reported that men consuming 6 grams of whey protein supplemented with leucine, isoleucine, and valine experienced less protein synthesis than those who consumed whey protein supplemented with just leucine. Additionally, research indicates that valine may cause insulin resistance in muscle, which can hinder muscle growth and increase body fat accumulation. This highlights the importance of focusing on leucine supplementation for optimal post-workout recovery and muscle growth.

Leucine, more than other branched-chain amino acids, is the most critical chemical that activates the mTOR pathway. Consuming leucine after exercise is likely more effective and cost-efficient than consuming BCAAs. The addition of isoleucine and valine may impede the benefits of leucine due to competition for transport into muscle cells. The BCAAs share the same active transport system into cells, and indeed, isoleucine and valine have been shown to inhibit leucine absorption.

For best results as an anabolic trigger, take 5 grams of leucine on an empty stomach 15-30 minutes before a post-workout meal. Taking pure leucine on an empty stomach ensures a better spike in blood levels compared to taking it with food, as food can slow leucine's absorption. When taken on an empty stomach, leucine acts as a powerful metabolic switch that turns on muscle protein synthesis. It increases mTOR activity for several hours after training. When leucine is taken after resistance exercise and before a protein-rich meal containing essential amino acids, it triggers greater protein synthesis for improved recovery and greater gains, showcasing the benefits of amino acids for muscle gain. (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)

• Amino Acid Leucine Benefits: Leucine is an essential amino acid that plays a critical role in muscle recovery and growth. It is particularly effective in stimulating the mTOR pathway, which is essential for muscle protein synthesis.
• Leucine Supplementation: Leucine supplementation can significantly enhance muscle recovery and protein synthesis, making it an invaluable component of any fitness regimen aimed at muscle growth and recovery.
• Essential Amino Acids for Muscle Gain: While leucine is a standout, incorporating a balanced intake of essential amino acids further supports muscle protein synthesis and overall muscle health.
• Amino Acid Supplements: Supplements containing amino acids, particularly leucine, are beneficial for athletes and fitness enthusiasts looking to maximize their muscle gain and recovery potential.

Reference:

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