Effects of later dinner timing on subsequent metabolic function and nocturnal sleep in healthy young women

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.

We conducted a randomized crossover trial with two dinner timing conditions: 1 h and 5 h before habitual bedtime. Each intervention lasted 6 days (Day 0 to Day 5), including a baseline day (Day 0) and 4 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.

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 = 0.013) and reduced sleep efficiency (SE, p = 0.040) and significantly higher wake after sleep onset (WASO, p = 0.017), Arousal Index (p = 0.041), number of stage-shifts (p = 0.016), and Stage-Shift Index (p = 0.003). 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.

Dinner consumed 1 h before bedtime was associated with reduced sleep continuity and stability, while only transient changes in postprandial glucose dynamics were observed. In healthy young women, eating close to bedtime may affect sleep architecture, warranting further investigation.