Some evidence suggests that there exists an association between obesity and shortened sleep duration. The exact reason for this association is not understood, but research has shown that a disturbed sleep pattern can result in a decrease in insulin sensitivity in as little as two nights. This may results from endocrine disruption following the curtailment of various phases of sleep, perhaps slow wave sleep (SWS). Some evidence suggests that sleep deprivation may also result in a positive energy balance. Increased insulin resistance and positive energy balance both could explain the association between disturbed sleep and obesity seen in epidemiological studies. In fact, recent research shows that a disturbed sleep pattern is detrimental to the duration of the most important sleep phases, and can cause physical exhaustion and metabolic changes that could result in weight gain and increase risk of obesity.
Research1 published in the American Journal of Clinical Nutrition in 2011 used 15 healthy male subjects in a randomised crossover study that aimed to investigate the effect of sleep disruption on energy metabolism. Energy expenditure, substrate oxidation and physical activity were measured in a respiratory chamber twice in 48 hours and subjects were monitored by electroencephalograph to determine sleep phases. During the daytime subjects were not allowed to sleep, and at night sleep was either 8 hours continuous or an hourly wake up disruption pattern via alarms of various frequencies. Sleep disruption lead to reductions in SWS, rapid eye movement (REM) sleep and total sleeping time. This did not cause any significant differences in total energy expenditure, but did cause increases in physical activity that raised activity induced energy expenditure, contributed to no doubt by having to get up to turn off the alarm.
In addition to increased physical activity, exhaustion, sleepiness, respiratory quotient and carbohydrate oxidation were elevated following disrupted sleep, when compared to continuous sleep. However, the disrupted sleep patterns caused a decrease in fat oxidation, suggesting that substrate utilisation had shifted and metabolism was altered. The increase in respiratory quotient (shift from fat oxidation to carbohydrate oxidation) agrees with some other studies and may result from an increased snacking seen following sleep deprivation that has been reported by other authors (here). Although increase physical activity was detected in the subjects following sleep deprivation, it is interesting to speculate on the longer-term implications of exhaustion reported by the subjects and the increased carbohydrate oxidation that may deplete glycogen stores. It is possible that both of these factor may eventually lead to reduced physical activity and weight gain.
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