BACKGROUND: Epidemiologic studies show an inverse or U-shaped relation between sleep duration and BMI. Decreases in total energy expenditure (TEE) and physical activity have been suggested to be contributing factors.
OBJECTIVE: The objective was to assess the effect of sleep fragmentation on energy metabolism and energy balance in healthy men.
DESIGN: Fifteen healthy male subjects [mean ± SD BMI (in kg/m(2)): 24.1 ± 1.9; age: 23.7 ± 3.5 y] were included in a randomized crossover study in which energy expenditure, substrate oxidation, and physical activity (by radar) were measured twice for 48 h in a respiration chamber while subjects were monitored by electroencephalography to determine slow-wave sleep (SWS), rapid eye movement (REM) sleep, and total sleeping time (TST). During 2 nights, sleep (2330-0730 h) was either fragmented or nonfragmented.
RESULTS: Fragmented sleep led to reductions in TST, SWS, and REM sleep (P < 0.001). TEE did not differ (9.96 ± 0.17 compared with 9.83 ± 0.13 MJ/d, NS) between the sleep groups, nor did the components of energy expenditure, with the exception of activity-induced energy expenditure (AEE; 1.63 ± 0.15 compared with 1.42 ± 0.13 MJ/d for fragmented and nonfragmented sleep, respectively; P < 0.05). Physical activity, exhaustion, sleepiness, respiratory quotient (RQ), and carbohydrate oxidation were elevated in comparison with nonfragmented sleep [physical activity counts: 2371 ± 118 compared with 2204 ± 124 counts/d, P < 0.02; exhaustion: 40.1 ± 3.8 compared with 21.8 ± 2.4 mm (by using a visual analog scale; VAS), P < 0.001; sleepiness: 47.4 ± 4.2 compared with 33.9 ± 4.6 mm (VAS), P < 0.001; RQ: 0.94 ± 0.04 compared with 0.91 ± 0.03, P < 0.05; and carbohydrate oxidation: 346.3 ± 23.8 compared with 323.7 ± 22.5 g/d, P < 0.05], whereas fat oxidation was reduced (29.1 ± 9.1 compared with 61.0 ± 6.6 g/d, P < 0.01).
CONCLUSIONS: Fragmented compared with nonfragmented sleep induced reductions in the most important sleep phases, which coincided with elevated AEE, physical activity, exhaustion, and sleepiness. RQ and carbohydrate oxidation increased and fat oxidation decreased, which may predispose to overweight. This trial is registered at www.who.int/ictrp and www.trialregister.nl as NTR1919.