How we rate
“Strong” = several concordant meta-analyses or systematic reviews. “Moderate” = one synthesis, or several controlled trials. “Limited” = early trials only. The rating is about the quality of the studies, not about how useful the supplement is.
Leucine
In the elderly, leucine at mealtimes restarts muscle protein synthesis and helps a little in cases of sarcopenia. In young people who weight train, four trials find no extra muscle or strength.
Benefits
- Restarts muscle protein synthesis in elderly men: with 5 g of leucine at each of the three meals for 3 days, 1.57% turnover per day versus 1.48% under placebo at rest, and 1.87% versus 1.71% in the trained leg, whether the diet is high or low in protein.
- Improves the muscular response to meals in elderly individuals: 4 g of leucine at each of the three meals for 2 weeks increased muscle protein synthesis at rest and after a low-protein meal.
- Makes a small dose of whey as effective as a large one in young men: 6.25 g of whey supplemented up to 5 g of leucine stimulated muscle protein synthesis as much as 25 g of whey.
- Helps the sarcopenic elderly individual a little: 6 g per day for 13 weeks improved walking time, lean mass index, and expiratory muscle strength compared to placebo, in 50 individuals over 65 living in a facility.
- Adds about 1 kg of lean mass in the elderly: +0.99 kg on average compared to control groups across 16 studies and 999 individuals, especially in sarcopenic individuals, without a strength gain.
Precautions
Well tolerated at 6 g per day for 13 weeks in elderly individuals, and between 1.2 and 6 g per day in studies from the 2019 review. Very few studies have sought the maximum safe dose, particularly in elderly or ill individuals. Limitations: in young people who weight train, leucine adds neither muscle nor strength: nothing at 3 g per day for 8 weeks, nothing at 10 g per day for 12 weeks in trained men, and a placebo group that progresses just as much for 12 weeks. It does not protect the muscle of an immobilized leg: 7.5 g then 15 g per day for 7 days slowed neither muscle wasting nor strength loss in young men. In elderly men eating enough protein, 7.5 g per day for 3 months (healthy) or 6 months (type 2 diabetic) changed neither muscle mass, nor strength, nor blood glucose. Making more protein does not mean gaining muscle: the meta-analysis in the elderly finds higher muscle synthesis, but no difference in total or leg lean mass. Evidence in sarcopenic individuals is of low quality, and several reviews combine leucine alone with leucine-enriched proteins, often with vitamin D.
Recommended dosage
6 g per day in sarcopenic elderly individuals; 4 to 5 g at each of the three meals in trials on muscle synthesis.
How to take it
- For whom: positive results involve individuals over 65, especially sarcopenic ones; in young people who weight train and eat enough protein, trials find nothing.
- Dose against sarcopenia: 6 g per day for 13 weeks in the placebo-controlled trial; studies from the 2019 review range from 1.2 to 6 g per day.
- At mealtimes: trials on muscle synthesis provide 4 to 5 g of leucine at each of the three main meals.
- Alone or with proteins: in sarcopenic elderly individuals, leucine alone and without exercise did not improve markers of the condition; combined with proteins, it did.
- With vitamin D: most protocols that lead to a gain in lean mass add vitamin D to leucine.
- Trial duration: from 3 days for muscle synthesis to 6 months in elderly diabetic men.
- What does not work: 3 g per day for 8 weeks or 10 g per day for 12 weeks of weight training in young people, nor 7.5 to 15 g per day for 7 days of an immobilized leg.
Did you know?
In a 12-week weight training trial in 75 young men, the placebo group gained as much muscle (2.2 kg on average for all groups) as the leucine group: all ate 600 to 800 kcal more per day than at baseline.
What the studies say
This meta-analysis compiled data to explore the effect of leucine supplementation in elderly individuals with sarcopenia. The results suggest that leucine may show trends toward improving muscle strength, muscle quality, and physical performance. A high dose of leucine was associated with a significant improvement in appendicular muscle mass and walking speed. However, the beneficial therapeutic impact of leucine alone is limited without concomitant additional therapy.
Huang C, Hsieh MH. — Nutrients (2025) — View the source study
Pairs well with
- Whey proteinTested together in young men: 6.25 g of whey supplemented up to 5 g of leucine stimulated muscle protein synthesis as much as 25 g of whey. In another trial, only the full dose of whey prolonged this effect after exercise.
- Vitamin DTested together in the sarcopenic elderly: in the 2025 meta-analysis, the leucine and vitamin D group had more limb muscle mass than the control group, and most of the positive protocols in the 2019 review combine both.
- BCAA / Essential Amino AcidsTested together in people aged 65 to 75: an essential amino acid blend containing 40% leucine, taken for 12 weeks, increased lean mass and improved certain physical tests.
For information only: not a substitute for medical advice. Dietary supplements are not a replacement for a varied, balanced diet. Learn more