Evidence that shortened period of sleep could be a risk factor for weight gain and obesity has grown over the past decade. Concurrent with the obesity epidemic, numerous studies have reported a parallel epidemic of chronic sleep deprivation. Sleep is important in maintaining energy balance (i.e. acute sleep deprivation impact the normal secretion of ghrelin and decreases leptin plasma levels). Surprisingly, in humans, there is no direct evidence that a shortened night has direct effect on energy metabolism during the following day.