L-Leucine
amino acids
L-Leucine is a branched-chain amino acid (BCAA) essential for muscle protein synthesis and energy metabolism. It activates mTOR signalling pathways critical for muscle growth and recovery, particularly during resistance training and caloric restriction.
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Benefits
Dosage
Typical Dose
2-5g per day
Upper Limit
20g per day
Timing
With meals or around training for optimal muscle protein synthesis
Forms & Bioavailability
Free-form powder
Excellent absorption; rapid intestinal uptake with peak plasma levels within 30-60 minutes
Capsules
Good absorption; convenient dosing with slightly delayed release compared to powder
BCAA complex
Good; often combined with isoleucine and valine for synergistic effects on muscle protein synthesis
Side Effects
Interactions
Research Summary
Substantial evidence demonstrates L-Leucine's role in stimulating mTOR-dependent muscle protein synthesis, with studies showing benefits for post-exercise recovery and preservation of lean mass during caloric deficits. Research indicates doses of 2-3g are sufficient to maximally stimulate protein synthesis when consumed with adequate total protein intake and carbohydrates.
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The Bottom Line on L-Leucine
L-Leucine is well-researched with strong evidence supporting its primary benefits.It is most commonly used for muscle protein synthesis and exercise recovery and performance. As with any supplement, individual results vary. Start with the lower end of the dosage range and assess for 4-8 weeks before adjusting.
About Our Research
This profile is compiled from peer-reviewed research published on PubMed, the NIH Office of Dietary Supplements, and established nutritional science databases. Dosages reflect clinically-studied amounts from human trials where available. We update profiles as new research emerges. This is not medical advice — consult a healthcare professional before supplementing.
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Goal Guides for L-Leucine
See how L-Leucine can help with specific health goals: