Presleep Whey but Not Casein Protein Ingestion Improves Sleep Quality After Resistance Exercise When Compared With an Isocaloric Control in Resistance Trained Individuals

Presleep protein supplementation can be a strategy for athletes to achieve daily protein requirements and to sustain amino acid supply during sleep. Food intake before sleep can affect sleep quality. However, the effects of different milk protein fractions on sleep quality have not been directly compared. In a randomized, double-blind, crossover trial, nine young, healthy, and resistance-trained men (n = 5) and women (n = 4) (age: 24 ± 2 year; body mass index: 24.4 ± 2.9 kg/m2) performed resistance exercise sessions on three occasions followed by ingestion of either 40 g of whey (WHEY), casein (CASEIN) protein, or an isocaloric maltodextrin control (CON) 30 min before bedtime. Sleep quality was assessed using actigraphy, heart rate variability, and a subjective sleep questionnaire. Gastrointestinal symptoms were monitored; exercise performance and delayed onset of muscle soreness were evaluated the next day. Presleep whey protein ingestion improved sleep-onset latency (9.0 [8.0-11.0], 16.0 [10.0-19.0], and 19.0 [15.0-27.0] min in WHEY, CASEIN, and CON, respectively); sleep efficiency (96% [96-98], 96% [94-96], and 93% [91-96]); total sleep time (400 [374-404], 390 [365-412], and 363 [358-412] min); and subjective sleep rating (8.0 [7.0-9.0], 7.0 [5.0-7.0], and 6.0 [5.0-7.0]) compared with CON (all p < .05) but not CASEIN (all p > .05). WHEY led to a significant reduction in delayed onset of muscle soreness 12 and 24 hr posttraining when compared with CON (p < .05). There were no differences in heart rate variability variables, gastrointestinal symptoms, and exercise performance between treatments (all p > .05). Presleep whey protein ingestion may enhance sleep quality after resistance training and reduce muscle soreness without affecting gastrointestinal symptoms and exercise performance in healthy young adults.