Our objective was to clarify the effect of sleep curtailment on energy intake (EI) and physical activity under free-living conditions. Participants were 16 healthy women aged 21-22years. A randomized crossover trial design was used to compare a short sleep condition (SS): 4h/night (2:00-6:00) and a control sleep condition (CS): 7h/night (23:00-6:00). Each condition comprised 3 consecutive nights. Sleep duration was assessed using a wristwatch-type accelerometer at home. All living activities except sleeping were free-living. Physical activity was assessed using a tri-axial accelerometer, and was categorized by intensity level (sedentary; sedentary to light; moderate to vigorous). Participants were asked to purchase and consume meals with visible nutrient information. EI was evaluated by adding values from these food labels. Mean sleep duration in the two conditions was significantly different (4.3±0.3 vs. 7.1±0.4h, p<0.01). For the shared wakefulness period in the two conditions (6:00-23:00), step counts and physical activity were not significantly different. Sedentary time (878±61 vs. 727±40min, p<0.01), and sedentary to light-intensity activity time (1122±18 vs. 932±63min, p<0.01) were significantly increased in SS (waking time, 06:00-02:00) compared with CS (waking time, 06:00-23:00). However, these significant effects were clearly attenuated after adjustment for awake time (p>0.05). Total EI was not significantly different between conditions (8.64±0.82 vs. 8.46±1.28MJ, p>0.05), nor were leptin levels (p>0.05), but insulin and cortisol levels after SS were significantly higher than after CS (p<0.05). In this study, physical activity was increased in the SS condition and attributed to differences in awake time between conditions. However, there were no differences in EI. Further studies to investigate the effect of sleep curtailment on weight gain through stress and insulin resistance are necessary.
Keywords: Energy intake; Insulin; Leptin; Physical activity; Sleep curtailment.
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