The Summary
In a randomized, double-blind, crossover study, nine resistance-trained young adults consumed either 40 grams of whey protein, casein protein, or a carb-based control drink 30 minutes before bed following an evening workout. Researchers used actigraphy, heart rate tracking, and questionnaires to measure sleep quality. Compared to the control, consuming whey protein significantly reduced the time it took to fall asleep, improved overall sleep efficiency, increased total sleep time, and lowered muscle soreness the next day. Casein protein did not show these same significant benefits over the control.
Why this is interesting
Casein is traditionally favored as the slow-digesting presleep protein for muscle recovery, while fast-digesting whey is typically reserved for post-workout. This study challenges that convention by showing that presleep whey, rather than casein, significantly improved objective sleep metrics—like falling asleep faster—and reduced post-exercise muscle soreness compared to a carbohydrate control. For active individuals, swapping your nighttime casein shake for whey after late-day training could be an easy way to optimize both your sleep quality and muscle recovery simultaneously.