L-Leucine, Unflavored by Nutricost is a high-purity supplement providing 5 grams of L-leucine per serving, an essential branched-chain amino acid (BCAA) with a central role in regulating muscle protein synthesis (MPS). L-Leucine acts not only as a building block for proteins but also as a key signaling molecule that activates the mTOR pathway, a critical regulator of muscle growth and repair. This dual function makes leucine a primary target for interventions in sarcopenia, age-related muscle loss, and conditions involving protein malnutrition.
The 5 g dose aligns precisely with clinical research demonstrating efficacy in enhancing myofibrillar protein synthesis, particularly when protein intake is suboptimal or in older populations with anabolic resistance. Studies show that 5 g of leucine added to low-protein meals can maximize post-exercise muscle synthesis [1], and when combined with resistance training, it improves fat-free mass and strength in midlife and older adults [2][3]. While benefits are most evident in those with low baseline muscle mass or protein intake, the isolated use of leucine without adequate total protein may limit long-term anabolic effects.
Quick Summary
Full transparency: exact amount of L-Leucine (5 g) is clearly listed with no proprietary blends or hidden ingredients.
The 5 g dose of L-Leucine is at the clinical midpoint for sarcopenia, resistance training, and low-protein meal augmentation, making it highly effective for its intended purposes. As a primary ingredient at clinical dose, efficacy is strong despite lack of supporting ingredients.
L-Leucine in powder form has high bioavailability and rapid absorption. Free-form amino acids like this are more readily utilized than protein-bound forms, earning a +10% credit for high-absorption delivery.
Generally safe at 5 g/day, but potential for GI discomfort and interactions with levodopa. Contraindicated in maple syrup urine disease. Long-term safety of high-dose isolated leucine is not fully established.
Suggested: 1 serving/day to reach clinical midpoint
Why Take This Product
Key Benefits
Who Should Take This
Potential Side Effects
Ingredient Breakdown
This product contains only one ingredient: L-Leucine. It is classified as a primary ingredient due to its presence in the product name, high dose (5 g), and central role in the product’s intended benefits. No supporting ingredients are present.
Primary Ingredients
L-Leucine
Essential branched-chain amino acid; stimulates muscle protein synthesis via mTOR pathway
L-Leucine is a key regulator of muscle protein synthesis, functioning both as a substrate and a signaling molecule. It is particularly effective in older adults and those with low protein intake.
Practical Recommendations
- Optimize Timing With Protein Or Exercise: Take 5 g of L-Leucine with resistance exercise or alongside low-protein meals to maximize muscle protein synthesis, especially in older adults.
- Combine With Adequate Total Protein Intake: Ensure daily protein intake is sufficient (1.2–2.0 g/kg/day); isolated leucine without adequate protein may not yield optimal muscle benefits.
- Monitor For Gastrointestinal Tolerance: Start with a lower dose if sensitive, and increase gradually to 5 g to assess tolerance.
- Avoid In Maple Syrup Urine Disease: Contraindicated in individuals with MSUD due to impaired leucine metabolism.
Is it Safe?
L-Leucine is safe for most individuals at the 5 g dose, but caution is advised in specific populations. It should be avoided in maple syrup urine disease and used carefully in those on levodopa therapy. Gastrointestinal side effects are possible at high doses, and long-term isolated use without adequate total protein intake may limit benefits and pose unknown risks.
Safety & Considerations
- Contraindication: Do not use if you have maple syrup urine disease (MSUD).
- Drug Interaction: May interfere with levodopa absorption; separate dosing by at least 2–3 hours.
- Adverse Effect: High doses may cause gastrointestinal discomfort in sensitive individuals.
Reports for Similar Products
The Science
The efficacy of this product is driven entirely by its 5 g dose of L-Leucine, which falls within the clinically effective range of 3–6 g/day for enhancing muscle protein synthesis and improving body composition. This dose is supported by multiple studies showing benefits in older adults, those with sarcopenia, and individuals undergoing resistance training.
Adding leucine to a low-protein beverage enhanced myofibrillar protein synthesis in young men post-exercise; 5 g dose was optimal.
5 g/day leucine with resistance training increased fat-free mass and strength in untrained midlife women.
Leucine supplementation showed beneficial effects on sarcopenia criteria, including lean mass and physical performance.
Leucine supplementation improves sarcopenia-related parameters in older adults, including muscle mass and strength.
L-leucine and BCAA supplementation may improve malnutrition and sarcopenia in chronic liver disease.
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