Protein powder · Evidence
Each point below summarizes specific sources, linked by number to the reference list at the bottom. Where the research is thin or mixed, we say so.
Grouped by how much research backs each outcome. A stronger group means more consistent results across more studies, not a bigger effect.
A meta-analysis of 49 randomized trials (1,863 healthy adults doing resistance training for at least 6 weeks) found protein supplements added small extra gains: 2.49 kg more on a one-rep max, 0.30 kg more fat-free mass, and larger muscle fibers. The extra gain in fat-free mass was smaller in older people and larger in people already trained.[1]
In the same meta-analysis, supplementing beyond a total protein intake of about 1.62 g per kg of body weight per day gave no further gain in fat-free mass. Total intake counts food and powder together.[1]
The NIH exercise fact sheet says athletes need about 1.2 to 2.0 g of protein per kg of body weight a day, from food and supplements combined.[2]
The NIH exercise fact sheet reports no safety concerns at the daily intakes recommended for athletes, up to about 2.0 g per kg of body weight, and lists no known side effects. It doesn’t cover contaminants such as heavy metals, so we don’t make claims about them here; each product page shows whatever independent testing we could find.[2]