More and more studies are showing that poor sleep patterns and not enough sleep are associated with weight gain. Although we are not quite sure of the underlying mechanism, studies are pointing towards how appetite control signals from the brain are altered by sleep restriction. Restricted sleep may increase the release of an appetite-stimulating hormone called ghrelin and reduce the production of the fullness-feeling hormone leptin. These changes in hormones may lead to an increase in food consumption without any increase in energy expenditure.
In a recent sleep deprivation study (PNAS, Mar 2013), participants were sleep deprived by a total of 4 hours per night, over 5 nights. The poor sleeping patterns resulted in a small increase in energy expenditure (5%), but this extra burning of energy from being awake for longer was more than offset by an increase in food intake, especially after dinner. An average weight gain of 0.82kg was observed in just 5 days. Surprisingly, the hormone levels observed were in favour of a lowering of appetite but this clearly was not observed. One theory now being offered is that circadian rhythms may be also playing a role. When the participants reverted back to their normal sleeping patterns there was a reduction in food intake and a small amount of weight loss. These studies clearly demonstrate the importance of sleep for weight control.