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Sleep deprivation makes the day drag and appears to put a drag on metabolism too, causing the body to use less energy, according to a European study.

The results, reported in the American Journal of Clinical Nutrition, add to evidence that sleep loss can promote weight gain - not just by boosting hunger but also by slowing the rate at which calories are burned.

The study suggests that getting plenty of sleep might prevent weight gain, said Christian Benedict of Uppsala University in Sweden, who led the study.

"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," he wrote.

Previous studies have linked sleep deprivation with weight gain and also shown how disrupted sleep also disrupts levels of stress and hunger-related hormones during waking hours.

To help identify the exact mechanisms by which a lack of sleep might have these effects, Benedict and his colleagues put 14 male university 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 indicators of their metabolic rate.

They found that even a single night of missed sleep slowed metabolism the next morning, reducing energy expenditure for tasks like breathing and digestion by 5 percent to 20 percent, compared with the morning after a good night's sleep.

The young men also had higher morning levels of blood sugar, appetite-regulating hormones such as ghrelin, and stress hormones such as cortisol after sleep disruption.

Still, the sleep loss did not boost the amount of food the men consumed during the day.

A number of studies have observed that people who sleep five hours or less are more prone to weight gain and weigh-related diseases such as type-2 diabetes. But those studies do not prove that sleep loss causes weight gain.

Experts said that factors such as lifestyle and diet might add to obesity risks and that it was not clear that sleep deprivation led to obesity.

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Todd Balazovic is a reporter for the Metro Section of China Daily. Born in Mineapolis Minnesota in the US, he graduated from Central Michigan University and has worked for the China Daily for one year.