A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength in healthy adults.
Level 1 - systematic review of randomized trials
Systematic review and meta-analysis of randomized controlled trials
PubMed 28698222 · doi:10.1136/bjsports-2017-097608
What was done
Systematic review, random-effects meta-analysis, and meta-regression of randomised controlled trials evaluating dietary protein supplementation during resistance exercise training lasting at least 6 weeks in healthy adults. Databases searched included Medline, Embase, CINAHL, and SportDiscus. A two-phase breakpoint analysis evaluated the relationship between total daily protein intake and changes in fat-free mass (FFM).
What was found
Across 49 studies with 1,863 participants, protein supplementation significantly increased gains during prolonged training: one-repetition-maximum strength increased by 2.49 kg (95% CI: 0.64 to 4.33, p < 0.05), FFM increased by 0.30 kg (95% CI: 0.09 to 0.52, p < 0.05), muscle fibre cross-sectional area (CSA) increased by 310 µm² (95% CI: 51 to 570, p < 0.05), and mid-femur CSA increased by 7.2 mm² (95% CI: 0.20 to 14.30, p < 0.05). The impact on FFM was reduced with increasing age (-0.01 kg, 95% CI: -0.02 to -0.00, p = 0.002) and was larger in resistance-trained participants (0.75 kg, 95% CI: 0.09 to 1.40, p = 0.03). Total protein intakes exceeding 1.62 g/kg/day provided no further gains in FFM.
Why it matters
This review establishes a quantitative benchmark (~1.6 g/kg/day) for optimal daily protein intake to maximize resistance training-induced muscle hypertrophy and strength gains in healthy adults.
Limits
The abstract does not detail specific protein sources, timing strategies, or the methodological quality and risk of bias of the included trials. Findings apply to healthy adults and may not generalize to clinical or catabolic populations.
Cited by
- supports Daily protein intake beyond 1.5 to 1.6 grams per kilogram of body weight does not yield additional increases in muscle mass in clinical studies.