Leucine Supplement: Why 7.5 g a Day Built No Muscle in Two Trials
Quick Answer: Leucine on its own has not built muscle in older adults in the trials that tested it. In two randomised trials, men around 71 years old took 2.5 g of leucine with each main meal (7.5 g a day) for three months and for six months; neither group gained muscle mass or strength compared with placebo. A meta-analysis explains the puzzle: leucine reliably raised the rate of muscle protein synthesis, yet produced no significant gain in lean body mass or leg lean mass. Where leucine has helped is as part of a protein supplement, and mainly in people who already have sarcopenia: a leucine-enriched whey supplement added 0.17 kg of limb muscle in 13 weeks in 380 sarcopenic older adults. If you want the leucine effect, get it from enough protein, not from a leucine powder.
Leucine is the amino acid with the best story in muscle science. It acts as a signal that switches on muscle protein synthesis, and older muscle responds less to that signal than younger muscle does. The logical next step was obvious: add extra leucine to meals and restore the response. Researchers tested exactly that, for months, with good methods. The results are the reason this page does not recommend a leucine supplement.
The trials that gave leucine alone
The cleanest tests came from Maastricht University. In a 2009 trial in the American Journal of Clinical Nutrition, Verhoeven and colleagues randomised 30 healthy men with an average age of 71 to 2.5 g of leucine or placebo with each main meal for three months, 7.5 g a day. Muscle mass was measured by CT and DXA scans and strength by one-repetition maximum. No changes in muscle mass or strength were seen in either group, and there was no improvement in insulin sensitivity, HbA1c or blood lipids.
Two years later the same group repeated the design for twice as long in a higher-risk group. Leenders and colleagues, in the Journal of Nutrition, gave 60 men with type 2 diabetes, average age 71, the same 7.5 g a day or placebo for six months. Lean tissue mass in the leucine group was 61.9 kg at the start and 62.0 kg at six months. The placebo group went from 62.2 kg to 62.2 kg. Strength, body fat, muscle fibre characteristics and blood sugar control did not change either.
| Trial | Who | Leucine | Result vs placebo |
|---|---|---|---|
| Verhoeven 2009 | 30 healthy men, mean age 71 | 2.5 g with each meal, 3 months | No change in muscle mass or strength |
| Leenders 2011 | 60 men with type 2 diabetes, mean age 71 | 2.5 g with each meal, 6 months | Lean mass 61.9 to 62.0 kg (placebo 62.2 to 62.2 kg); no change in strength |
One detail in the second trial matters for interpreting both: the authors concluded leucine did not help elderly men with diabetes who habitually consume adequate dietary protein. Men who already ate enough protein were already getting the leucine that comes with it.
Why the lab signal did not become muscle
A 2015 meta-analysis in the British Journal of Nutrition by Xu and colleagues pooled nine randomised trials in older people and found both halves of the story at once. The muscle protein fractional synthetic rate rose significantly with leucine (standardised difference 1.08). Lean body mass did not (0.18, not significant), and neither did leg lean mass.
Synthesis rate is measured over hours after a meal. Muscle mass is what accumulates over months, after synthesis and breakdown are both counted. A supplement can push the short-term measurement up without changing the long-term one, and leucine is the clearest example of that gap in nutrition research. Headlines built on the first measurement are why leucine is sold as a muscle builder.
Where leucine did help: inside protein, in sarcopenia
The results change when leucine comes as part of a protein supplement and the people taking it are already losing muscle.
- Komar et al., 2015 (Journal of Nutrition, Health & Aging): 16 studies, 999 older people. Leucine supplementation, mostly as leucine-rich protein, increased lean body mass by 0.99 kg and body weight by 1.02 kg compared with controls, with larger effects in people with sarcopenia. It did not improve hand grip or knee extension strength.
- Lee et al., 2022 (Archives of Gerontology and Geriatrics): 6 randomised trials, 699 older adults with sarcopenia. Leucine-rich protein supplements improved muscle strength (standardised difference 0.79) and a combined measure of strength, mass and performance.
- PROVIDE, 2015 (Journal of the American Medical Directors Association): 380 sarcopenic older adults took a vitamin D and leucine-enriched whey protein supplement or an isocaloric control twice a day for 13 weeks. The supplement group gained 0.17 kg more limb muscle and was 1.01 seconds faster on the chair-stand test. Hand grip and the overall physical performance score (SPPB), the trial’s primary outcomes, improved in both groups with no difference between them.
Put together: for someone already eating enough protein, extra leucine did nothing measurable. For someone with sarcopenia, a leucine-rich protein supplement produced small gains in muscle, and in one analysis in strength. Protein was doing much of that work.
What this means in practice
- Start with total protein. Older adults often eat less than they need, and every protein food carries leucine with it. Our guide to how much protein you need after 60 gives grams per day by body weight.
- If you use a supplement, make it a protein. The positive trials used leucine-rich protein, most often whey, not leucine powder. Our comparison of EAAs, BCAAs and whey explains why a complete protein beats isolated amino acids.
- Pair it with resistance training. Supplements added modest amounts of muscle; training is what builds it. See how to build muscle after 60.
- Dileucine is a different product with thinner evidence in older adults. It is two leucine molecules bonded together; our dileucine review covers the studies, which were in young men.
- If you are ill or bed-bound, HMB, a leucine metabolite, has its own evidence for protecting muscle when you cannot train.
What the trials support: a protein supplement, not a leucine one. The positive sarcopenia trial used whey protein, which provides leucine along with every other essential amino acid. An unflavoured whey protein can be mixed into foods you already eat. Compare unflavoured whey protein on Amazon.
Affiliate link: as an Amazon Associate we earn from qualifying purchases, at no extra cost to you. People with kidney disease should ask their doctor before increasing protein.
Frequently Asked Questions
Does leucine build muscle?
Not as a standalone supplement in older adults, in the trials that tested it. Men around 71 taking 7.5 g of leucine a day gained no muscle mass or strength over three months, or over six months in men with diabetes. Leucine does raise the rate of muscle protein synthesis after a meal, but a meta-analysis of nine trials found that did not translate into more lean body mass.
How much leucine should an older adult take?
The trials give no evidence that adding leucine powder helps if you already eat enough protein. The two long trials used 2.5 g with each of three meals, 7.5 g a day, without benefit. A better target is total daily protein, which brings leucine with it; our protein guide gives amounts by body weight.
Is leucine good for sarcopenia?
Leucine-rich protein supplements have helped. A meta-analysis of six trials in 699 older adults with sarcopenia found improved muscle strength, and the PROVIDE trial found a leucine-enriched whey supplement added 0.17 kg of limb muscle and improved chair-stand time over 13 weeks. Those were protein supplements with extra leucine, not leucine alone.
Is leucine better than whey protein?
No evidence says so. Whey contains leucine plus the other essential amino acids, and the positive trials in older adults used leucine-enriched whey or other leucine-rich protein. Leucine alone raised muscle protein synthesis in short studies but did not increase muscle over months.
Does leucine help blood sugar?
Not in the long trials. Neither three months in healthy older men nor six months in older men with type 2 diabetes changed HbA1c, insulin sensitivity or blood lipids.
What is the difference between leucine and dileucine?
Dileucine is two leucine molecules joined together, sold as a newer form that may be absorbed differently. Its human studies have been in young men, and it has not been tested for muscle gain in older adults the way leucine has.
The Bottom Line
Leucine is the right molecule with the wrong delivery. It switches on muscle building in the short term, but 7.5 g a day on top of a normal diet did not add muscle or strength in older men over three or six months. The benefit shows up when leucine comes packaged in protein, and mostly in people who are already losing muscle. Eat enough protein, lift something, and if you need a supplement, choose a protein rather than a single amino acid.
Sources
- Verhoeven S, Vanschoonbeek K, Verdijk LB, et al. Long-term leucine supplementation does not increase muscle mass or strength in healthy elderly men. American Journal of Clinical Nutrition, 2009;89(5):1468-1475. PMID 19321567. 30 men, mean age 71; 2.5 g leucine per main meal (7.5 g/d) for 3 months; no change in muscle mass or strength. Checked 24 September 2026.
- Leenders M, Verdijk LB, van der Hoeven L, et al. Prolonged leucine supplementation does not augment muscle mass or affect glycemic control in elderly type 2 diabetic men. Journal of Nutrition, 2011;141(6):1070-1076. PMID 21525248. 60 men, mean age 71, 6 months; lean mass 61.9 to 62.0 kg (leucine) vs 62.2 to 62.2 kg (placebo). Checked 24 September 2026.
- Xu ZR, Tan ZJ, Zhang Q, Gui QF, Yang YM. The effectiveness of leucine on muscle protein synthesis, lean body mass and leg lean mass accretion in older people: a systematic review and meta-analysis. British Journal of Nutrition, 2015;113(1):25-34. PMID 25234223. 9 RCTs; fractional synthetic rate SMD 1.08; lean body mass 0.18 (P = 0.318); leg lean mass not significant. Checked 24 September 2026.
- Komar B, Schwingshackl L, Hoffmann G. Effects of leucine-rich protein supplements on anthropometric parameter and muscle strength in the elderly: a systematic review and meta-analysis. Journal of Nutrition, Health & Aging, 2015;19(4):437-446. PMID 25809808. 16 studies, 999 participants; lean body mass +0.99 kg, body weight +1.02 kg; no effect on grip or knee extension strength. Checked 24 September 2026.
- Lee SY, Lee HJ, Lim JY. Effects of leucine-rich protein supplements in older adults with sarcopenia: a systematic review and meta-analysis. Archives of Gerontology and Geriatrics, 2022;102:104758. PMID 35777246. 6 RCTs, 699 participants; muscle strength SMD 0.794. Checked 24 September 2026.
- Bauer JM, Verlaan S, Bautmans I, et al. Effects of a vitamin D and leucine-enriched whey protein nutritional supplement on measures of sarcopenia in older adults, the PROVIDE study. Journal of the American Medical Directors Association, 2015;16(9):740-747. PMID 26170041. 380 sarcopenic adults, 13 weeks; appendicular muscle +0.17 kg; chair stand -1.01 s; grip and SPPB no between-group difference. Checked 24 September 2026.
