Meta-analysis: protein supplementation augments resistance-training strength & fat-free mass, benefit plateau ~1.62 g/kg/day
Participants
n=1863 participants across 49 randomised controlled trials of resistance training (≥6 weeks) with dietary protein supplementation, healthy adults.
Key Findings
Protein supplementation during RET significantly increased (all p<0.05) gains in 1RM strength +2.49 kg (95% CI 0.64–4.33), fat-free mass +0.30 kg (0.09–0.52), muscle-fibre CSA +310 µm² (51–570) and mid-femur CSA +7.2 mm² (0.20–14.30).
The effect on FFM was reduced with increasing age (−0.01 kg per year; p=0.002 in the abstract, p=0.02 in the Results and key messages (corrected 2026-10-12, full text)) and greater in resistance-trained individuals (+0.75 kg, p=0.03).
Break-point analysis: protein supplementation beyond a total intake of 1.62 g/kg/day produced no further RET-induced gains in FFM (~1.6 g/kg/day in the conclusion). The 95% CI of the break point (1.03–2.20 g/kg/day) is reported in the full text, checked 2026-09-27.
Practical Application
Meta-analysis of 49 RCTs, n=1863: protein supplementation during ≥6 weeks of resistance training added +2.49 kg to 1RM and +0.30 kg fat-free mass; the FFM benefit stops at a total intake of ~1.6 g/kg/day (break point 1.62), is smaller with age and larger in trained lifters.
Target ~1.6 g/kg/day as the practical ceiling for maximising RET muscle/strength in most athletes; more isn't harmful in this data but adds little to lean mass.
Older muscle less responsive → masters sit at/above the top of the band + adequate stimulus (REF-348).
Default answer to "will more protein build more muscle?": yes, up to ~1.6 g/kg/day, then diminishing returns.
Limitations
1.62 breakpoint is a group average with a wide CI (full text); outcomes FFM/strength not performance; effects modest, depend on baseline diet/training.
How this entry was checked and changed
Why this level
regraded 2026-09-27 from A+: a single systematic review/meta-analysis (rubric: A); A+ is reserved for several concordant SR/MAs or an umbrella review
Content correction 2026-09-27
Break-point CI "1.03–2.20" is not in the abstract -> labelled full text. Added fibre and mid-femur CSA effects and the age/training-status coefficients from the abstract; Participants section added.
Level A+ -> A per rubric (single SR/MA). Cross-references given refIds.
Lines labelled "full text; not checked against the abstract" were checked against the open-access full text (PMC5867436): every number in them appears there; relabelled "full text, checked 2026-09-27".
Full text (checked 2026-10-12)
The 49 studies (1962 to 2016) had participants aged 35±20 years, with 10 studies in resistance-trained participants and 14 study groups of exclusively female participants (full text).
Supplements gave 36±30 g/day of protein (young 42±32, old 20±18 g/day), with 24±11 g after exercise, and mean baseline intake was ~1.4 g/kg/day (full text).
The 1.62 g/kg/day break point came from a biphasic regression of 42 study arms (723 participants) that was not statistically significant (p=0.079) (full text).
RET alone (13±8 weeks) raised 1RM by 27±22 kg and FFM by 1.1±1.2 kg, and protein added 2.49 kg (9%) and 0.30 kg (27%) respectively (full text).
1RM gain from protein was 0.99 kg (p=0.12) in untrained and 4.27 kg (p=0.02) in trained participants, and FFM gain was 0.15 kg (p=0.08) versus 1.05 kg (p<0.0001) (full text).
FFM gain from protein was 0.06 kg in older (>45; 67±7 years) versus 0.55 kg in younger (<45; 24±4 years) participants, with only 13 studies in older individuals (full text).
Correction: the entry gives the age effect on FFM as "p=0.002" (as in the abstract), while the results and key messages report p=0.02 (full text).