Past about 1.6 g per kg a day, extra protein added nothing
Across 49 training trials protein supplements bought 0.30 kg of fat-free mass. Above roughly 1.62 g per kg a day the curve flattens; 16 weeks at double that added nothing.
What the study found
Extra protein stopped adding lean mass above 1.6 g per kg a day
Pooled across 49 resistance-training trials, protein supplements bought 0.30 kg of fat-free mass and 2.49 kg on a one-rep max, months of them for a third of a kilo. Above roughly 1.62 g per kg a day the fat-free mass curve flattens, and sixteen weeks at double that added nothing.
The caveat · Most already ate 1.2 g per kg
In about 80% of the pooled trials people were already eating at least 1.2 g per kg a day, so this measures going from enough to more, not from too little to enough. The 1.62 figure comes with a range running from 1.03 to 2.20, wide enough to be a region rather than a line. Most trials ran six to twelve weeks. Effects shrank with age and were larger in people already training.