Protein's muscle payoff stalls past 1.62 g/kg/day

Protein supplements are the default purchase for anyone who lifts weights, but the honest question is how much of the resulting muscle and strength is down to the powder rather than the training. Just as importantly, there is a widespread assumption that more protein keeps producing more muscle, which drives intakes far above official recommendations. Settling that requires pooling many trials, because individual studies are typically too small to detect the modest effects involved. This review set out to quantify the benefit and to find the point at which extra protein stops paying off.

The authors systematically searched Medline, Embase, CINAHL and SportDiscus for randomised controlled trials combining dietary protein supplementation with resistance exercise training lasting at least six weeks. They pooled 49 studies with 1863 participants using random-effects meta-analysis, then ran meta-regressions with four pre-specified covariates. Outcomes included one-repetition-maximum strength, fat-free mass, muscle fibre cross-sectional area and mid-femur cross-sectional area. To locate a possible ceiling, they applied a two-phase break point analysis relating total protein intake to changes in fat-free mass.

Protein supplementation significantly increased one-repetition-maximum strength by 2.49 kg (95% CI 0.64 to 4.33) and fat-free mass by 0.30 kg (95% CI 0.09 to 0.52). Muscle size also increased, with muscle fibre cross-sectional area up 310 µm2 and mid-femur cross-sectional area up 7.2 mm2. The benefit to fat-free mass shrank with increasing age (-0.01 kg per year) and was larger in people already resistance-trained (an extra 0.75 kg). The break point analysis found that supplementation beyond a total protein intake of 1.62 g/kg/day produced no further training-induced gains in fat-free mass.

This is one of the most cited quantifications of protein's supporting role in resistance training, and it reframes supplements as a modest amplifier of training rather than a driver of growth. The 1.62 g/kg/day figure has since become shorthand for the point of diminishing returns, though it describes where the averaged data flattened, not a hard biological wall. The age and training-status findings complicate simple recommendations, hinting that older lifters may need a different approach and that novices gain plenty from the training alone. Open questions include whether higher intakes matter during energy restriction and how individual variation sits around that group-level ceiling.

This is a reason to treat total daily protein as the number that matters and to see supplements as a convenient way to reach it rather than a growth stimulus in their own right. The absolute effects are real but modest, so no powder will compensate for inadequate training. If your overall intake is already comfortably above roughly 1.62 g/kg/day, the pooled evidence gives little reason to expect more muscle from adding still more. Training experience appeared to increase the payoff, which suggests the value of dialling in intake grows as your training does.