Here's a dreamy weight-loss plan: take a nap. That's the message from work by Sanjay Patel at Case Western Reserve University in Cleveland, Ohio. His study of more than 68 000 women has found that those who sleep less than 5 hours a night gain more weight over time than those who sleep 7 hours a night.

Controlling for other differences between the groups, Patel found that women who slept 5 hours or less gained 0.7 kilograms more on average over 10 years than 7-hour sleepers. The short-sleeping group was also 32 percent more likely to have gained 15 kilograms or more, and 15 percent more likely to have become obese.

Significantly, the short-sleepers consumed fewer calories than those who slept 7 hours, says Patel, who presented his results this week at the American Thoracic Society International Conference in San Diego, California. This finding overturns the common view that overeating among the sleep-deprived explains such weight differences.

Lower metabolic rate resulting from less sleep may be the reason behind the weight gain, Patel suggests. "It obviously also suggests that getting people to sleep more might be a relatively easy way to help people lose weight," he says.