If you're a young man who already lifts weights and eats enough protein, doing strength training twice a week for 12 weeks will make you stronger and build more muscle — and taking leucine supplements won't make any extra difference compared to taking a sugar pill.
See the scientific wording
In resistance-trained young men consuming 1.8 g protein per kg body weight daily, 12 weeks of twice-weekly resistance training leads to significant increases in muscle strength and size, with no difference in outcomes between those taking 10 g/day of leucine and those taking a placebo.
Very strong evidence
Randomized trialsOne good-quality study supports this claim.
What the research says
1 study reviewedSupporting (1)
Leucine Supplementation Has No Further Effect on Training-induced Muscle Adaptations
Randomized Controlled TrialHuman2020
The study gave some guys 10 grams of leucine daily and others a fake pill, while both groups trained and ate the same amount of protein. Both groups got just as strong and muscular, so leucine didn’t help extra — which means the claim is right.
Contradicting (0)
No contradicting studies found yet
That doesn't mean it's settled — it just means no study has tested the opposite.
Quality-weighted scoring: we follow the GRADE framework — each study is rated High, Moderate, Low, or Very Low based on study design, methodology rigor, and risk of bias. A single high-quality RCT can outweigh several weaker observational studies.
Scores reflect study quality, not just count.
Score breakdown, mechanism chain, raw evidence, ideal studies needed & 1 supporting study
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If you're a young man who already lifts weights and eats enough protein, doing strength training twice a week for 12 weeks will make you stronger and build more muscle — and taking leucine supplements won't make any extra difference compared to taking a sugar pill.
Evidence from Studies
Supporting (1)
Community contributions welcome
Leucine Supplementation Has No Further Effect on Training-induced Muscle Adaptations
The study gave some guys 10 grams of leucine daily and others a fake pill, while both groups trained and ate the same amount of protein. Both groups got just as strong and muscular, so leucine didn’t help extra — which means the claim is right.
Contradicting (0)
Community contributions welcome
Score Breakdown
No multi-axis breakdown available yet. The overall Pro / Against score above is the best signal.
- No clinical evidence is available; the score reflects mechanistic plausibility only.
What Would Prove This
Per GRADE and EBM methodology, here is what ideal scientific evidence would look like to definitively prove or disprove this claim, ordered from strongest to weakest.
Systematic Review & Meta-Analysis of RCTs on Leucine Supplementation vs Placebo for Muscle Strength and Hypertrophy in Protein-Adapted Resistance-Trained Young Men Over 12 Weeks
All included RCTs must involve resistance-trained young men, 1.8 g/kg protein intake, twice-weekly resistance training for 12 weeks, 10 g/day leucine vs placebo, with pre/post measures of muscle strength (e.g., 1RM) and size (e.g., MRI/DEXA)
Double-Blind, Placebo-Controlled RCT of 10 g/day Leucine vs Placebo on Muscle Strength and Hypertrophy in Resistance-Trained Young Men Over 12 Weeks with 1.8 g/kg Protein Intake
Random assignment of participants to leucine (10 g/day) or placebo, matched for protein intake (1.8 g/kg), twice-weekly resistance training, 12-week duration, blinded assessors, primary outcomes: 1RM and muscle cross-sectional area via DEXA/MRI
Prospective Cohort Study Comparing Muscle Gains in Resistance-Trained Young Men Taking 10 g/day Leucine vs Placebo Over 12 Weeks with Controlled Protein Intake
Enroll resistance-trained young men consuming 1.8 g/kg protein, assign to leucine or placebo group based on self-selection, monitor training compliance and muscle changes over 12 weeks with standardized assessments
Case-Control Study of Individuals with Significant Muscle Strength Gains vs Minimal Gains After 12 Weeks of Resistance Training, Comparing Leucine Supplementation Use
Identify 'cases' (those with >10% increase in 1RM and muscle mass) and 'controls' (those with <2% increase) after 12 weeks of training and 1.8 g/kg protein, then retrospectively assess leucine use
Cross-Sectional Survey of Muscle Strength and Size in Resistance-Trained Young Men Reporting Leucine Use vs Non-Use with 1.8 g/kg Protein Intake
Survey a group of resistance-trained young men at one time point, collect data on leucine use (yes/no), protein intake (self-reported), training frequency, and measure muscle strength and size