Overnight energy expenditure determined by whole-body indirect calorimetry does not differ during different sleep stages.

BACKGROUND Sleep has been associated with the regulation of energy balance, yet the relation between sleep stages and energy expenditure remains unclear. OBJECTIVE The objective was to investigate the relation between sleep stages and energy expenditure, with sleep stage and overnight energy expenditure patterns taken into account. DESIGN Thirteen subjects aged (mean ± SD) 24.3 ± 2.5 y with a BMI (in kg/m(2)) of 23.6 ± 1.7 slept in a respiration chamber while sleep was polysomnographically recorded to determine wake after sleep onset (WASO), slow-wave sleep (SWS), and rapid eye movement (REM) sleep. Energy expenditure was calculated during each sleep stage for the whole night and separately for sleeping metabolic rate (SMR; ie, 3-h period during the night with the lowest mean energy expenditure) and non-SMR. RESULTS Energy expenditure and sleep stages showed characteristic patterns during the night, independently of each other. Sleep stages exerted no effect on energy expenditure during the whole night, except for WASO compared with SWS (P < 0.05) and WASO compared with REM sleep (P < 0.05). During the SMR and non-SMR periods of the night, no overall effect of sleep stage on energy expenditure, except for WASO compared with SWS (P < 0.05) and WASO compared with REM sleep (P < 0.01) during the non-SMR period of the night, was found. Energy expenditure and activity counts during the night were positively correlated (r = 0.927, P < 0.001). CONCLUSIONS Energy expenditure does not vary according to sleep stage overnight, except for higher energy expenditure during wake episodes than during SWS and REM sleep. Coincidence of the sleep stage pattern and the overnight energy expenditure pattern may have caused accidental relations in previous observations. This trial was registered at http://apps.who.int/trialsearch as NTR2926.