Systematic review and meta-analysis of protein intake to support muscle mass and function in healthy adults.
Level 1 - systematic review of randomized trials
Systematic review and meta-analysis of 74 randomized controlled trials.
PubMed 35187864 · doi:10.1002/jcsm.12922
What was done
Researchers conducted a systematic review, three-level random-effects meta-analysis, and meta-regression of 74 randomized controlled trials to evaluate the effect of increasing daily protein intake on lean body mass (LBM), muscle strength, and physical functional test performance. The analysis included healthy, non-obese adults and conducted subgroup analyses stratified by resistance exercise participation, age (<65 vs. ≥65 years), and daily protein dosage.
What was found
Protein supplementation during resistance exercise resulted in a small increase in LBM (SMD = 0.22, 95% CI 0.14 to 0.30, P < 0.01; 62 studies). Significant LBM effects occurred at 1.2–1.59 g/kg/day for adults ≥65 years old and at ≥1.6 g/kg/day for adults <65 years old. For strength during resistance training, protein intake ≥1.6 g/kg/day slightly improved lower-body strength (reported SMD = 0.40, 95% CI 0.09 to 0.35, P < 0.01; 19 studies) and bench press strength in adults <65 years old (SMD = 0.18, 95% CI 0.03 to 0.33, P = 0.01; 32 studies). Effects on handgrip strength were unclear, and effects on physical function test performance were minimal.
Why it matters
This review clarifies the modest magnitude of benefit from supplemental protein on muscle mass and strength, showing that benefits are primarily realized when combined with resistance exercise and vary by age-dependent intake thresholds.
Limits
The total number of individual participants was not reported in the abstract. Evidence certainty was rated low for strength outcomes and moderate for lean mass. In the absence of resistance exercise, protein effects were not clearly supported, and functional performance test improvements were marginal.