How much protein do I need a day?
What the studies we have published say — strongest evidence first. Every claim below links to the paper it came from.
In an 8-week randomised trial, resistance-trained men taking 30 g/day whey protein plus 10 g/day collagen gained more muscle mass, lumbar spine bone density and strength than whey alone, collagen alone or placebo.
preliminary · human dataSmall double-blind RCT: 40 resistance-trained men across four groups, so about 10 per arm, over only 8 weeks; muscle mass came from bioelectrical impedance rather than a criterion method, and the reported gains, including the spine bone density change, are unusually large and unusually consistent for such a short trial, so independent replication matters.
Across 49 randomised trials with 1863 healthy adults, adding protein supplements to resistance training increased fat-free mass by 0.30 kg and one-rep-max strength by 2.49 kg on average. Once total protein intake passed roughly 1.62 g/kg/day, extra protein added nothing further to fat-free mass gains.
well supported · human dataMeta-analysis of 49 RCTs in healthy adults training for at least six weeks, so the pooled effects are solid but small in absolute terms; the 1.62 g/kg/day ceiling comes from a break-point analysis of group averages, not an individualised threshold, and the senior author discloses dairy-industry grant support.
A meta-analysis of 74 randomised trials found that eating more protein adds small extra gains in lean mass and lower-body strength for healthy adults doing resistance training. Lean-mass benefits appeared at 1.2-1.59 g of protein per kg per day in adults 65 and over, and at 1.6 g/kg/day or more in younger adults.
well supported · human dataMeta-analysis of 74 RCTs in healthy, non-obese adults; the lean-mass effect was small (SMD 0.22, moderate-level evidence), strength evidence was rated low, and some authors have food-industry ties.
A meta-analysis of whole-food dietary interventions in adults aged 50 and over found they raised daily protein intake by 12.2 g/day compared with controls, with bigger effects when programmes ran longer, used individual counselling and set an absolute protein target.
preliminary · human dataSystematic review of 16 studies (n = 1712, 33% male) with a meta-analysis of 11 controlled trials (n = 1207) in community-dwelling older adults; protein intake was self-reported dietary data, the confidence interval was wide (+5.0 to +19.4 g/day), and muscle or strength outcomes were not the endpoint.
Pooling seven randomised trials in adults aged 60 and over, adding protein or amino acids at breakfast did not improve lean mass, grip strength or lower-limb strength. The evidence was judged very uncertain, and in trials without exercise the extra morning protein was linked to slightly lower total daily energy intake.
preliminary · human dataSystematic review and meta-analysis of only 7 RCTs totalling 305 older adults; the authors rate certainty as very low, effect estimates all crossed zero, and they call for further high-quality trials.
In a meta-analysis of 10 randomised trials with 1,154 participants, whey protein supplementation improved muscle mass and gait speed in older adults diagnosed with sarcopenia, and combining it with resistance training significantly increased handgrip strength.
well supported · human dataMeta-analysis of 10 RCTs (1,154 older adults with diagnosed sarcopenia, community and hospital settings mixed); the authors say more studies are needed to validate the results.
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This page collects what our published, cited studies say; it is information, not medical advice. Have a different question? Ask it here.