The Study
Leucine Supplementation Has No Further Effect on Training-induced Muscle Adaptations
This study is like a fair test where two groups of guys lifted weights and one group took extra leucine pills and the other took fake pills. After 12 weeks, both groups got just as strong and muscular — so the leucine pills didn’t help any more than the fake ones.
Analysis score
Maximum 90 for a randomized controlled trial.
Where the score came from
Scientists gave some guys extra leucine powder and others a fake powder, while both groups lifted weights. They wanted to see if the leucine made muscles grow more.
Where does this study sit?
Reviews of RCTs (Meta-analyses)
Max 100Randomized Trials
Max 90Reviews of Cohort Studies
Max 85Cohort Studies
Max 72Reviews of Case-Control Studies
Max 63Case-Control Studies
Max 58Cross-Sectional & Case Series
Max 50Expert Opinion
Max 575 / 100
Quality score
Participants are randomly assigned to treatment or control groups, minimizing bias. The gold standard for testing whether an intervention causes an effect.
Key takeaways
Summary
Based on the study abstract and findings.
- 1No — adding 10g of leucine daily didn’t help at all when people already ate enough protein.
- 2Both groups got stronger by about 20% and muscles grew by about 8%.
- 3The leucine group didn’t grow more than the placebo group.
Score breakdown, methodology, conflicts of interest, evidence analysis & raw study data
Publication
Journal
Medicine & Science in Sports & Exercise
Year
2020
Authors
Isabel Thomazi de Andrade, B. Gualano, Victoria Hevia-Larraín, Juarez Neves Junior, M. Cajueiro, F. Jardim, R. L. Gomes, G. Artioli, Stuart M Phillips, P. Campos-Ferraz, H. Roschel
Related Content
Claims (6)
If you're a young man who lifts weights regularly, eating 1.8 grams of protein per kilogram of your body weight every day is enough to build as much muscle as you can from training—adding extra leucine powder won't help you get any bigger or stronger.
If you're a young guy who lifts weights and you take 10 grams of leucine powder split into two doses a day, it won't make you eat more or less protein or leucine from your regular food.
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.
Taking leucine supplements won’t help young athletes build more muscle, get stronger, or recover faster—even though leucine is known to trigger a muscle-growth signal in the body.
If you're a young guy who lifts weights and already eats enough protein, taking extra leucine pills for 12 weeks won't make you stronger or build more muscle in your thighs than just lifting weights by itself.
If you're a young man who already eats enough protein and works out with weights, taking extra leucine won't help your muscles grow any more — your muscles just can't use more than a certain amount, no matter how much you give them.
Not medical advice. For informational purposes only. Always consult a qualified healthcare professional before making health decisions.