The 1.6 g/kg figure is real and traceable to a specific, high-profile paper. Morton et al. pooled data from 49 studies with 1,863 participants and found that dietary protein supplementation significantly increased one-repetition-maximum strength, fat-free mass, and muscle fibre cross-sectional area during prolonged resistance training, and that protein supplementation beyond total protein intakes of 1.62 g/kg/day resulted in no further resistance-training-induced gains in fat-free mass.

The paper's own wording is that "protein intakes at amounts greater than approximately 1.6 g/kg/day do not further contribute to RET-induced gains in FFM."

However, the precision implied by "1.6" is much softer in the original paper. The figure caption reports the break point as 1.62 g protein/kg/day with p=0.079, and a 95% confidence interval of 1.03 to 2.20. That p-value means the breakpoint itself did not reach conventional statistical significance, and the confidence interval extending to roughly 2.2 g/kg/day is the statistical basis for the widely cited practical range of 1.6 to 2.2 g/kg/day; 1.62 is the point estimate of the plateau, not a hard ceiling.

The claim that research is "consistent" on this is where the evidence diverges most sharply. A re-examination of Morton's own supplementary figures argues that the meta-analysis contains data suggesting the breakpoint, if one exists, is probably higher than 1.62 g/kg, and that these supplementary data received far less attention than the headline breakpoint analysis despite being no less valid. Other meta-analyses used different statistical approaches and reached different conclusions. Tagawa et al. concluded that slightly increasing protein intake by 0.1 g/kg/d in a dose-dependent manner across a range from 0.5 to 3.5 g/kg/d may increase or maintain lean body mass , a dose-response framing rather than a plateau framing. A summary of the Nunes meta-analysis notes that whether intakes were categorized as low, medium, or high, or analyzed by meta-regression, going above 1.6 g/kg was associated with improved hypertrophy.

Professional guidance sits above the claim's figure, not at it. The ISSN position stand recommends 1.4 to 2.0 g/kg/day for exercising individuals, well above the general population recommendation of 0.8 g/kg.

The ISSN also notes that resistance-trained subjects on low calorie diets may need higher intakes, ranging from 2.3 to 3.1 g/kg/day.

The debate remains live and unsettled. One 2025 review notes that while Morton reported benefits plateauing beyond approximately 1.6 g/kg/day, other work by Antonio and colleagues found intakes exceeding 3 g/kg/day were tolerated and associated with favorable body composition. Researchers aligned with the original meta-analysis maintain their position: a 2025 McMaster analysis states that meta-analyses pooling dozens of trials show supplementation benefits plateau at about 1.6 g/kg/day, and that beyond that additional protein does not increase lean mass or strength.