It takes just five consecutive days of inadequate sleep to increase food intake in excess of energy needs, leading to weight gain.

Scientists found that average expenditure of energy per day increased by about 5% when participants were allowed to sleep for up to five hours, compared with a sleeping period of up to nine hours.

Participants with insufficient sleep overate despite changes in levels of the hormones leptin, ghrelin and peptide YY, which signalled excess food intake.

Source: Proceedings of the National Academy of Sciences 2013, doi:10.1073/pnas.1216951110.