Strongest evidence: The evidence for all 6 outcomes is rated as low strength, so no outcomes reach high or moderate certainty. Among these, improved handgrip strength has the most studies (4 papers; 2 beneficial, 2 neutral) with a moderate effect size, primarily in older adults with sarcopenia or undergoing resistance training. Reduced postprandial glucose (3 studies; 2 beneficial, 1 neutral) shows a moderate effect with a consistent dose range of 12.5–55 g premeal, though all trials were under 7 days long.
Mixed or weaker evidence: For increased muscle mass (3 studies; 2 beneficial, 1 neutral), effects were small and seen mostly in clinical populations (type 2 diabetes, MASLD). Improved muscle strength (3 studies; 2 beneficial, 1 neutral) had moderate effects but only 1 study reached statistical significance, and one substituted pea protein for whey. Reduced interleukin-6 levels (3 studies; 1 beneficial, 2 neutral) showed only a small effect in a single meta-analysis of sarcopenic older adults. Increased lean mass (3 studies; 1 beneficial, 2 neutral) had mixed results with no consistent benefit across populations.
Effective dose patterns: Only one outcome, reduced postprandial glucose, reported a specific effective dose range (12.5–55 g premeal). No other outcome had a reproducible effective dose, and dose reporting was inconsistent across studies.
Population insights: The most consistent benefit appears in older adults, particularly those with sarcopenia or undergoing resistance training (for handgrip strength and muscle outcomes). Clinical populations (type 2 diabetes, MASLD, post-operative patients, hemodialysis patients) were studied in several outcomes, but generalizability to healthy adults or athletes remains unclear. One study on postprandial glucose included pregnant women with or without gestational diabetes.
Notable caveats: All 6 syntheses are based on only 3–4 studies, and the evidence strength is low across the board. Many individual studies did not reach statistical significance, indicating effects may be smaller or less consistent than the beneficial studies suggest. Study durations were short (often under 8 weeks, and as short as 7 days), limiting conclusions about long-term effects. Two outcomes had studies using pea protein instead of whey, and one used a suboptimal twice-weekly dosing schedule.