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
Morton, R.W., et al.British Journal of Sports Medicine, 2018DOI: 10.1136/bjsports-2017-097608
A meta-analysis of 49 resistance-training trials (1,863 adults). Extra protein increased muscle and strength gains up to about 1.62 g/kg/day, beyond which no further benefit appeared, setting a practical ceiling for how much protein lifters need.