Sleep restriction by sleep timing late night or early wake: The impact on physical activity and dietary intake in adults

Purpose: To date, few studies have assessed whether the timing of sleep restriction impacts physical activity and energy intake patterns. Thus, we aimed to quantify physical activity and energy intake during an early wake (EW) and late sleep (LS) period. Methods: Fourteen participants who met the inclusion criteria (sleep 7-9 h/night and a BMI of <40 kg/m(2)) participated in 3 crossover free-living conditions: normal sleep (NS, 7-9 h), EW (2-h early wake-time), and LS (2-h late to sleep) for 4 nights. Sleep duration (via Actiwatch), energy intake (via food diaries), and physical activity (via hip accelerometry) were recorded for 4 days/4 nights throughout each condition. Results: Sleep duration was reduced in both sleep restriction conditions compared to NS (p < 0.001) with no difference between sleep restriction conditions. Daily energy intake tended to increase in the LS condition (p = 0.056) but was unchanged during EW (p = 0.56). Fat (p = 0.031) and sodium (p = 0.039) intake were increased in the LS condition only compared to NS. During the EW condition, fat (p = 0.24) and sodium (p = 0.18) intake were not altered. No changes in carbohydrate or protein intake occurred between conditions. Daily steps tended to increase in the EW condition compared to NS (p = 0.058), while steps during the LS condition were unchanged (p = 0.28), with no differences between sleep restriction conditions. Conclusion: The timing of sleep curtailment differentially influences physical activity and EI the following day, such that EW results in increased physical activity, while LS leads to poorer dietary choices.