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.
A pooled analysis of 75 trials in 1,206 athletes found protein supplements improved endurance and strength compared with no supplement, but every statistically significant benefit came from trials where the protein group also took in more total energy. The gains may reflect extra calories rather than protein itself.
well supported · human dataTake the benefits with a pinch of salt: results pooled from 75 trials in 1,206 athletes, but every significant win came from studies where the supplement group also consumed more energy overall. Extra calories, not protein itself, may explain the edge.
Pooling 36 trials in 1,552 people doing resistance training, whey protein added the most lean mass versus placebo, about 1.24 kg on average, with benefits plateauing around 30 to 35 g per day; in adults aged 65 and over, whey's edge narrowed while casein climbed the rankings.
well supported · human dataFairly solid for whey's edge: results pooled from 36 trials in 1,552 people lifting for at least six weeks. The dose plateau is an exploratory estimate, and the older-adult comparison rests on just nine trials, so those two details deserve the most doubt.
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.
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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.