Protocol
Adequate dietary protein (1.2 to 1.6 g/kg/day)
Higher protein intake adds to the lean-mass and strength gains of resistance training; without training the pooled strength effect is nil, and the lean-mass effect shrinks with age.
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How this letter has changedLatest: October 2026 · Corrected.
The description said protein supports lean mass 'particularly in older adults'. The evidence runs the other way: Morton 2018 (PMID PubMed ID: the permanent number the US National Library of Medicine gives a published paper. Each one links to that paper's record on PubMed. 28698222) found the effect shrinks with age, Bhasin 2018 (PMID 29532075) was null at almost this record's dose in older men, and Obasi 2025 (PMID 41385355) found no benefit in healthy older people. Tagawa 2022 (PMID 36057893) shows the strength benefit depends on concurrent resistance training, now stated. Nunes 2022 (PMID 35187864) added with its industry ties, and the dairy-industry support behind Morton 2018 stated. Wu 2016 (PMID 26797090) relabeled as a narrative review. Endpoint The outcome a trial measures to decide whether the treatment worked, such as heart attacks, blood pressure or a symptom score. type set to surrogate (lean mass), which is what the grade rests on. Letter unchanged.PMID 28698222 PMID 29532075 PMID 41385355 PMID 36057893 PMID 35187864 PMID 26797090
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This is about eating more protein, about 1.2 to 1.6 grams per kilogram of body weight each day. In many trials of people doing strength training, extra protein added a little more lean muscle and strength. The gain stopped growing above about 1.6 grams per kilogram. It was also smaller in older people. In people who did not do strength training, extra protein did not add strength. No trials looked at disease or deaths.
Higher protein intake adds to the lean-mass and strength gains of resistance training; without training the pooled strength effect is nil, and the lean-mass effect shrinks with age. Randomized evidence on body-composition and strength endpoints.
Why this gradeThe reasoning, and what the grade does not cover.
Grade B on lean mass and strength during resistance training. A meta-analysis A study that pools the numbers from several trials into one combined estimate. of 49 randomized trials found added protein increased fat-free mass by 0.30 kg and one-repetition maximum by 2.49 kg, with no further gain above about 1.6 g/kg/day, and a smaller effect with age (Morton et al., 2018; PMID 28698222); the senior author discloses dairy-council support. A meta-analysis of 74 trials found a lean-mass gain in people resistance training (Nunes et al., 2022; PMID 35187864).
WHAT THIS GRADE DOES NOT COVERpeople who do not resistance train, where the pooled strength effect is nil; intakes above about 1.6 g/kg/day; and disease or mortality outcomes.
A grade describes the human evidence for a named use. It is not advice, and it is not a judgment on any individual prescription. How the letters are decided →
The evidence, in fullSix papers, each linked to its PubMed record.
Morton et al. (Br J Sports Med, 2018; PMID 28698222): meta-analysis of 49 randomized trials, 1,863 adults; protein supplementation during resistance training added 0.30 kg fat-free mass and 2.49 kg to one-repetition maximum, with no further gain above about 1.6 g/kg/day; the effect on fat-free mass fell with increasing age. The senior author discloses support from the US National Dairy Council, which funded some of the pooled trials. Nunes et al. (J Cachexia Sarcopenia Age-related loss of muscle mass and strength. Muscle, 2022; PMID 35187864): 74 randomized trials; lean mass gain with added protein in people resistance training (SMD 0.22), significant in those 65 and over at 1.2 to 1.59 g/kg/day; funded by ILSI Europe, with employees of nutrition companies among the authors. Tagawa et al. (Sports Med Open, 2022; PMID 36057893): 82 randomized trials; strength rose with protein only when resistance training was present (2.01 percent) and not without it (0.13 percent), with gains up to 1.5 g/kg/day; five authors are employees of a food company. Null in older adults: Bhasin et al. (JAMA Intern Med, 2018; PMID 29532075) randomized 92 functionally limited men aged 65 and over to 1.3 versus 0.8 g/kg/day for 6 months and found no difference in lean mass, strength, power, walking speed or well-being; Obasi et al. (Age Ageing, 2025; PMID 41385355), an overview of 33 meta-analyses, found no increase in muscle mass, strength or performance from protein supplementation in healthy older people, with benefit confined to those with long-term conditions, more so with exercise. Wu (Food Funct, 2016; PMID 26797090) is a narrative review and is context, not grade evidence. Grade B: replicated The same finding reproduced by a separate research group. A result seen once can be chance or bias; a replicated one is harder to explain away. randomized evidence on lean mass and strength, conditional on resistance training, with the benefit smaller or absent in older adults.
Daily protein intake using a 3-day food diary or app at baseline and monthly. Lean mass by DEXA at baseline and 6 months; grip strength quarterly. In older adults over 65, the lower bound of 1.2 g/kg may be insufficient during caloric restriction: 1.6 g/kg is more protective of lean mass during weight loss.
Evidence notes: review
Endpoint graded: Lean mass and strength during resistance training (surrogate)
Last reviewed: July 2026
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(protein supplementation[tiab] OR protein intake[tiab]) AND (lean mass[tiab] OR fat-free mass[tiab] OR muscle strength[tiab]) AND meta-analysis[pt] AND (older[tiab] OR resistance training[tiab] OR resistance exercise[tiab])Grades move when new trials publish. A free monthly email lists every grade EBL moved, with the reason and the trial behind it: the sign-up is on the Evidence Log →