Leucine

amino acid
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Leucine is one of three branched-chain amino acids (BCAAs), along with isoleucine and valine. As an essential amino acid, it cannot be produced by the body and must be obtained through diet or supplementation. It plays a role in various physiological processes, most notably acting as a stimulator of muscle protein synthesis. Leucine primarily activates the mTOR (mammalian target of rapamycin) pathway, which regulates cell growth, proliferation, and protein synthesis. This activation is involved in muscle repair, growth, and recovery following exercise. Beyond muscle building, leucine also contributes to the regulation of blood sugar levels and energy production. Due to its role in muscle metabolism, leucine is often used by athletes and those looking to maintain or increase muscle mass. It is frequently included in BCAA or complete amino acid formulations to support athletic performance, aid in recovery, and help prevent muscle breakdown, especially during intense training or calorie restriction.

Natural sources
Meat (beef, poultry, pork)FishEggsDairy products (milk, cheese, yogurt)Legumes (beans, lentils)Nuts (peanuts, almonds)Seeds (sunflower, pumpkin)Brown riceWhole wheatSoy products

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Optimal Dosage
Minimum2000 mg
Maximum5000 mg
Safety & Toxicity
4 safety notes
  • Individuals with Maple Syrup Urine Disease (MSUD) should avoid leucine due to inability to metabolize BCAAs.
  • Pregnant or breastfeeding women should consult a healthcare professional before supplementing.
  • Monitor blood sugar levels if diabetic, as high doses may influence glucose metabolism.
  • Excessive intake might lead to BCAA imbalance, potentially affecting niacin and vitamin B6 levels.

Studies

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Interactions

Positive Interactions

Isoleucine
Leucine, isoleucine, and valine are branched-chain amino acids (BCAAs) that work synergistically to stimulate muscle protein synthesis and improve muscle recovery.
Valine
As a fellow BCAA, valine cooperates with leucine to maximize muscle protein synthesis, reduce muscle breakdown, and enhance post-exercise recovery.
Creatine
Leucine can amplify the anabolic effects of creatine, potentially leading to greater gains in muscle mass and strength when combined, by further stimulating protein synthesis.
Glutamine
Leucine's role in stimulating muscle protein synthesis complements glutamine's benefits in muscle recovery, immune function, and maintaining cellular hydration.
Vitamin B6
Vitamin B6 is a crucial cofactor for the metabolism of amino acids, including leucine, optimizing its utilization for energy and protein synthesis pathways.
Proprietary Blend (Amino Acid/Protein)
Leucine is a vital component in many amino acid and protein blends, acting as the primary trigger for muscle protein synthesis, thus enhancing the overall efficacy of such formulations for muscle growth and repair.
Arginine
Arginine supports blood flow and nitric oxide production, which can enhance the delivery of nutrients, including leucine, to muscles, thereby supporting leucine's role in protein synthesis.
Lysine
As an essential amino acid, lysine is necessary for overall protein synthesis and tissue repair, supporting the comprehensive anabolic processes that leucine helps initiate.
METHIONINE
An essential amino acid, methionine plays a crucial role in initiating protein synthesis and various metabolic pathways, which complements and supports leucine's anabolic functions.
Phenylalanine
Phenylalanine is an essential amino acid required for overall protein synthesis, thereby supporting the availability of building blocks for muscle repair and growth stimulated by leucine.
Tryptophan
As an essential amino acid, tryptophan contributes to the complete amino acid profile needed for robust protein synthesis and overall physiological functions that aid recovery.
Histidine
An essential amino acid involved in protein synthesis and tissue repair, histidine supports the body's overall anabolic capacity, complementing leucine's muscle-building effects.
Glutamic Acid
As a major component of protein and a precursor to glutamine, glutamic acid supports the overall amino acid pool necessary for protein synthesis driven by leucine.
Alanine
Alanine is involved in the glucose-alanine cycle and nitrogen balance, which provides energy and supports metabolic processes critical for sustained muscle activity and recovery alongside leucine.
Glycine
Glycine is involved in collagen synthesis and neurotransmitter function, supporting connective tissue health and overall recovery, which complements the muscle repair effects of leucine.
Proline
Proline is critical for collagen formation and connective tissue health, important for structural integrity and recovery in conjunction with leucine's muscle protein synthesis benefits.
Tyrosine
Tyrosine, a non-essential amino acid, is involved in neurotransmitter synthesis, which can support mental focus and energy, indirectly benefiting physical performance where leucine aids muscle recovery.
Cysteine
Cysteine is a precursor to glutathione, a powerful antioxidant. By helping to reduce oxidative stress from intense exercise, cysteine can indirectly support the recovery process where leucine is active in muscle repair.