Acute Sleep Deprivation Shifts Substrate Utilization Toward Greater Fat Oxidation During Incremental Exercise in Recreationally Trained Adults.

Sleep deprivation alters metabolic homeostasis and substrate metabolism, but its effect on fat and carbohydrate utilization during exercise is unclear. This study examined the effects of one night of total and partial sleep deprivation on substrate utilization during a maximal fat oxidation test (MFO) in recreationally trained adults. Thirty-two recreationally trained young adults (16 females, 16 males) completed a randomized, counterbalanced crossover study with three sleep conditions: normal sleep (NS, 8 h), early sleep deprivation (ESD, 4 h), and total sleep deprivation (SD, 0 h). Sleep was monitored by wrist actigraphy and a researcher. The following morning, participants performed an incremental cycling test to determine MFO and carbohydrate oxidation (MCHO), absolute and relative to fat-free mass (FFM), Fatmax, and energy expenditure. Sleep condition affected MFO, ΜFO/FFM, MCHO, and MCHO/FFM (p < 0.05, ηp 2 > 0.137). Compared with ESD and NS, SD increased MFO (9% and 16%, p < 0.001, g = 0.54) and MFO/FFM (9% and 15%, p = 0.003, g = 0.61). MCHO (-14%, p = 0.041, g = 0.41) and MCHO/FFM (-15%, p = 0.035, g = 0.53) decreased in SD compared to NS. No differences were observed in Fatmax or energy expenditure. Sleep restriction increased resting heart rate (~5%, p = 0.027, ηp 2 = 0.114) and systolic blood pressure (~6%, p = 0.014, ηp 2 = 0.139). Subjective fatigue, confusion, sleepiness, and perceived exertion were higher after total sleep deprivation (p < 0.001). No sleep-by-sex interactions were observed. One night of total sleep deprivation shifts exercise substrate utilization toward greater fat oxidation and lower carbohydrate use without affecting Fatmax or energy expenditure. However, increased fatigue and perceived effort highlight the importance of adequate sleep for optimal exercise performance. Trial Registration: ClinicalTrial.gov identifier: NCT07015008.