Whey Protein and Increased Muscle Mass

Across 3 studies, 2 reported beneficial effects of whey protein on increased muscle mass, with effect sizes ranging from small to moderate. The median study duration was 28 days across 1 study that reported duration, though effects were observed in clinical populations including older adults, those with type 2 diabetes, and patients with MASLD. Evidence is preliminary due to the small number of studies and mixed populations.

• Studied populations: middle-aged and older adults undergoing resistance training, adults with type 2 diabetes mellitus, adults with MASLD

Caveats: Evidence base is small (only 3 studies) — conclusions should be considered preliminary. One systematic review (highest quality, evidence score 8) reported neutral findings despite noting whey as the most effective protein source, and its effect size was small; the other two studies were beneficial but in clinical populations (T2DM, MASLD) with small to moderate effects. Generalizability to healthy adults or athletes is unclear. Median study duration was short (28 days) and only reported in one study, limiting conclusions about long-term effects.