Conclusion: Dietary protein supplementation significantly enhanced changes in muscle strength and size during prolonged RET in healthy adults. Increasing age reduces and training experience increases the efficacy of protein supplementation during RET. With protein supplementation, protein intakes at amounts greater than ~1.6 g/kg/day do not further contribute RET-induced gains in FFM.
PubMed 28698222 ↗Leucine
The short answer. There isn't much data on Leucine yet — 25 mentions, 8 with a clear outcome — so treat these numbers as anecdotal. It is most often used for performance: 100% of 6 reports say that improved. It is well studied — 267 meta-analyses on PubMed.
From 25 mentions in total — the rest didn't say how it went and aren't counted.
What Leucine does, according to users
Of the people who reported each effect, the share who said it got better.
What the research says
Systematic reviews and meta-analyses from PubMed, with their published conclusions.
3+ meta-analyses or systematic reviews and 10+ randomized controlled trials in humans. The grade measures how much human research exists — read the conclusions below for what it found.
Conclusion: In studies using high-throughput metabolomics, several blood amino acids appear to be consistently associated with the risk of developing type 2 diabetes.
PubMed 27208380 ↗Conclusion: The benefits of nutritional interventions with various compositions for pressure ulcer prevention and treatment are uncertain. There may be little or no difference compared to standard nutrition or placebo. Nutritional supplements may not increase gastrointestinal side effects, but the evidence is very uncertain. Larger studies with similar nutrient compositions would reduce these uncertainties. No study investigated the effects of special diets (e.g. protein-enriched diet, vegetarian diet) on pressure ulcer incidence and healing.
PubMed 38345088 ↗Conclusion: In addition, the appendicular muscle mass significantly increased regardless of the presence of a concomitant physical exercise program; (4) Conclusions: Whey protein, leucine, and vitamin D supplementation can increase appendicular muscle mass in patients with sarcopenia. In addition, combining a physical exercise program with whey protein, leucine, and vitamin D supplementation can improve muscle strength and function.
PubMed 36771225 ↗Dosage people report
As stated by users — not a recommendation. Follow the label or your doctor.
Reported side effects
How often each side effect came up across all reports.
What users say
First-hand experiences, quoted verbatim. We show one positive and one negative where both exist.
“on a cut I ramp leucine intake through the roof (both through eating more protein generally and also through BCAA and pure luecine supplementation) and I find it helps me retain lean mass better.”
“even a small amount (3/4 grams leucine or 5/6 grams bcaa) before resistance training or sports makes a huuuuge difference in my doms”
“I only need L-Leucine, so that's what I take, 10mg before training fasted. It's supposed to help you build muscle by spiking insulin”
Other options for performance
User data from public discussions; research from PubMed. Information only, not medical advice — talk to a doctor before starting, stopping or combining anything. Data updated October 3, 2026. How we rate