A new report in the Proceedings of the National Academy of Science shows that lack of sufficient sleep for several sequential nights leads to weight gain. This is a potentially important step in determining the contributing factors to the current obesity epidemic.

We already knew that lack of sleep is a risk factor for weight gain and obesity. What we didn’t know was how that happens. Now we have a pretty good idea.

Scientists led by Kenneth P. Wright, Jr. at the University of Colorado, Boulder, used whole-room calorimetry in human subjects for two-weeks, to measure energy expenditure and food intake changes when going from the baseline condition (9-hr of sleep available for several days) to 5 consecutive days of only 5-hr of sleep available. Losing sleep did increase energy expenditure by 5%, but food intake went up way more than 5%, especially in women. Losing sleep, therefore, leads to overeating and weight gain, and can be a contributor to obesity.