Evidence Level
Strong
Whey and casein protein are among the most extensively studied supplements in sports science, with hundreds of RCTs and multiple meta-analyses confirming their efficacy. The key finding from Morton et al. (2018) — the largest meta-analysis to date — is that protein supplementation augments resistance training adaptations, but total daily protein intake matters far more than timing, source, or type. The practical protein dose-response plateaus at ~1.6 g/kg/day, with an upper confidence bound of ~2.2 g/kg. Whey is superior to casein, soy, and most plant proteins for acute MPS stimulation, primarily due to faster digestion and higher leucine content. Casein has a unique niche for overnight protein delivery.