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Protein and leucine

Expert groups conclude that older adults need more dietary protein than younger adults, and many older adults eat less than that. In randomised trials, eating more protein gave small extra gains in lean mass and leg strength in healthy adults doing resistance exercise, with little further gain above about 1.6 g per kilogram of body weight a day. Leucine supplements raised muscle protein synthesis in older adults without a measurable gain in lean mass. Plant and animal protein sources produced similar changes in absolute lean mass and strength, although many plant proteins carry less leucine, lysine or methionine. In healthy adults, higher-protein diets did not change kidney function in trials.

  • Longevity
  • Strength
  • Vegan

Evidence retrieved up to

What the research shows

In healthy adults without kidney disease, higher-protein diets did not adversely affect kidney function in randomised trials: glomerular filtration rate after the intervention was trivially higher on higher-protein diets, and the change from baseline did not differ from normal- or lower-protein diets.

Moderate certaintyFurther research may change the size of the effect.
Take care: see the safety noteNo clear effect

Who this is about

healthy adults without kidney disease

Practical note

Graded moderate: a 2018 meta-analysis of 28 randomised trials with 1358 participants; downgraded one level for the unclear risk of selection bias the authors report. Higher-protein arms were defined as at least 1.5 g/kg/day, at least 20 percent of energy, or at least 100 g of protein a day. Direction is no-effect because the claim concerns harm to kidney function and none was found: post-intervention GFR was trivially higher on higher-protein diets (SMD 0.19), which the authors call a trivial effect rather than a benefit or harm, and the change in GFR from baseline did not differ (SMD 0.11, not significant).

Safety note

This finding is limited to adults without kidney disease; the PROT-AGE group notes that older people with severe kidney disease not on dialysis may need to limit protein intake.

Sources

In older adults, leucine supplementation increased the rate of muscle protein synthesis in randomised trials, but did not measurably increase lean body mass.

Low certaintyFurther research is likely to change this.
No known concerns at usual amountsUnclear

Who this is about

older adults

Practical note

Graded low: a 2015 meta-analysis of nine randomised trials; the positive result is for a short-term surrogate (fractional synthetic rate), and lean mass showed no difference, so the evidence is downgraded for indirectness and imprecision.

Vegan note

Leucine content varies widely between plant proteins, so leucine matters most for diets built on a single low-leucine plant protein.

Sources

In healthy adults doing resistance exercise, increasing daily protein intake produced small additional gains in lean body mass and lower-body strength in randomised trials, with little further lean-mass gain at total intakes above about 1.6 g per kilogram of body weight a day.

Moderate certaintyFurther research may change the size of the effect.
No known concerns at usual amountsBenefit

Who this is about

healthy non-obese adults doing resistance exercise training

Practical note

Graded moderate: a 2022 meta-analysis of 74 randomised trials rated the lean-mass effect moderate-level evidence (strength gains low-level); effects on handgrip strength and physical function tests were unclear or marginal. A 2018 meta-analysis of 49 trials found no further lean-mass gain above total intakes of about 1.6 g/kg/day. Several authors of both reviews declared dairy or nutrition-industry funding. Training-specific detail sits in the plant-protein-resistance-training topic.

Sources

Expert groups conclude that older adults need more dietary protein than younger adults to maintain lean body mass and physical function, and a sizeable share of adults over 71 eat less protein than recommended.

Low certaintyFurther research is likely to change this.
Take care: see the safety noteBenefit

Who this is about

older adults (over 65)

Practical note

Graded low: the higher-need conclusion rests on an expert position paper and a narrative review drawing on metabolic studies, not on trials showing better function from a specific intake. The PROT-AGE group recommended an average of at least 1.0 to 1.2 g of protein per kilogram of body weight a day for people over 65, and more for those who are active or have acute or chronic illness; the 2025 review reports that 30 percent of men and 50 percent of women over 71 in the United States eat inadequate protein.

Vegan note

The 2025 review describes per-meal protein amounts from animal and plant sources alike as sufficient to maximise muscle protein synthesis in older populations.

Safety note

The PROT-AGE group names older people with severe kidney disease who are not on dialysis as an exception who may need to limit protein; protein targets in that group belong with their clinicians.

Sources

In randomised trials where total protein intake was generally above the recommended allowance, plant and animal protein sources produced similar changes in absolute lean mass and muscle strength, with a small advantage for animal protein in percent lean mass, mainly in adults under 50.

Low certaintyFurther research is likely to change this.
No known concerns at usual amountsNo clear effect

Who this is about

adults with protein intakes generally above the recommended dietary allowance

Practical note

Graded low: a 2021 meta-analysis of 16 randomised trials, with results differing by outcome (absolute versus percent lean mass) and by age subgroup, so downgraded for inconsistency and imprecision. Leucine contents measured in plant isolates ranged from 5.1 percent of protein for hemp to 13.5 percent for corn, against 9.0 percent for milk.

Vegan note

Many plant protein isolates contain less essential amino acid, leucine, lysine or methionine than animal proteins; laboratory analyses suggest combining plant protein sources gives a profile closer to animal protein.

Sources