Sleep well and stay slim.
That's the astonishing takeaway from a U.S. study looking at sleep, metabolism and eating habits of 16 men and women.
Researchers at the University of Colorado found that when subjects came up short on sleep, they experienced almost immediate weight gain.
As The New York Times reports, the healthy adults were effectively sealed off from the outside world, with every morsel of food strictly recorded and sleep schedules enforced.
The amount of oxygen they used and carbon dioxide they produced was also tracked during the two-week experiment.
Half the subjects were allowed nine hours of sleep during the first week, while the other half were accorded just five. Everyone could eat as much as they liked.
For the second week, the sleep allowances were reversed.
By the experiment's end, scientists found that staying up late resulted in a higher metabolism, causing the sleep-deprived group to burn an average of 111 additional calories per day.
But those extra burned calories were more than made up for by the fact that subjects were actually eating during those wakeful hours. By the end of the first week the sleep-deprived group had gained an average of two pounds each.
"Just getting less sleep, by itself, is not going to lead to weight gain," study lead Kenneth Wright of the university's Sleep and Chronobiology Laboratory said in press release. "But when people get insufficient sleep, it leads them to eat more than they actually need."
The study, published last week in The Proceedings of the National Academy of Sciences, found fast weight gain among the sleep-deprived regardless of gender.
In the abstract, researchers note, "Our findings suggest that increased food intake during insufficient sleep is a physiological adaptation to provide energy needed to sustain additional wakefulness; yet when food is easily accessible, intake surpasses that needed."
Wright suggested part of those extra pounds was a product of behavioral changes.
“We found that when people weren’t getting enough sleep they overate carbohydrates,” he said. “They ate more food, and when they ate food also changed. They ate a smaller breakfast and they ate a lot more after dinner.”
He added that part of the change was behavioral. Staying up late and skimping on sleep led to not only more eating, but a shift in the type of foods a person consumed.
Night owls managed to consume 6 per cent more calories. But when they were allowed more sleep, carbohydrates and fats yielded to healthier foods -- and once they started sleeping more, they began eating more healthfully, consuming fewer carbohydrates and fats.
The study adds to a growing body of evidence against lack of quality rest.
According to a recent British study, even our genes are not immune.
Researchers at the University of Surrey in England recorded activity at the genetic level among people who aren't getting enough sleep.
"It used to be thought that sleep was by the brain, of the brain, for the brain," Harvard Medical School researcher Dr. Charles Czeisler told the LA Times earlier this month. "Now it's recognized that it plays an important role in bodily functions."