Effects of Later Dinner Timing on Subsequent Metabolic Function and Nocturnal Sleep in Healthy Young Women

Objectives This study aimed to investigate the effects of dinner timing on subsequent sleep architecture and glucose metabolism in healthy young women, using objective and integrated physiological measures in a real-life setting. Methods We conducted a randomized crossover trial with two dinner timing conditions: 1 hour and 5 hours before habitual bedtime. Each intervention lasted six days (Day 0 to Day 5), including a baseline day (Day 0) and four intervention days (Days 1–4). Dinner provided 709–740 kcal, with consistent macronutrient composition across conditions. Overnight sleep electroencephalography (EEG) was recorded on Day 0 and Day 4, and continuous glucose monitoring (CGM) was conducted throughout the experimental period. An oral glucose tolerance test (OGTT) was performed after waking on Day 5. Results Thirteen healthy young women (21.4 ± 0.6 years) participated. On Day 4, the late-dinner condition (1 h before bedtime) resulted in significantly shorter total sleep time (TST, p = 0.011) and significantly higher sleep efficiency (SE, p = 0.005), wake after sleep onset (WASO, p = 0.021), arousal index (p = 0.034), number of stage-shifts (p = 0.020), and stage-shift index (p = 0.006). The iAUC for postprandial glucose showed a significant interaction (p = 0.042), with lower values on Days 3 and 4 than on Day 1 (p = 0.090). OGTT results showed no significant changes. Conclusion Consuming dinner 1 hour before bedtime adversely affected sleep architecture and transiently impaired glucose regulation, though glucose tolerance remained unchained. Sleeping immediately after the final meal may therefore be inadvisable for maintaining optimal sleep quality and metabolic function.