Just one night of lack of sleep can contribute to weight gain, say scientists.
It slows down the body's metabolism the next morning - meaning less energy, in the form of calories, is burnt off.
Previous studies have linked sleep deprivation with an increase in hunger-related hormones during waking hours.
"Our findings show that one night of sleep deprivation acutely reduces energy expenditure in healthy men, which suggests sleep contributes to the acute regulation of daytime energy expenditure in humans," the Daily Mail quoted Christian Benedict, who led the research at Uppsala University in Sweden, as saying.
He and his colleagues put 14 male students through a series of sleep 'conditions' - curtailed sleep, no sleep, and normal sleep - over several days, then measured changes in how much they ate, their blood sugar, hormone levels and metabolic rate.
Even a single night of missed sleep slowed metabolism the next morning, reducing energy expenditure for tasks such as breathing and digestion by between 5 and 20 per cent.
Sanford Auerbach, head of the Sleep Disorders Center at Boston Medical Centre, pointed out that sleep deprivation is a complex issue, with medication and other issues influencing sleep as well, and urged that the new findings be kept in context.
"They showed that we adapt to sleep deprivation and that some of these adaptations could theoretically contribute to obesity," he added, adding that it's not clear how chronic sleep loss influences hormone levels.