People who are sleep deprived for just one workweek tend to overeat and gain weight, according to a new study published Monday.
In a controlled lab test, 16 healthy adults were limited to just five hours of sleep over the course of five days—participants gained, on average, nearly 2 pounds and tended to eat meals later than expected. Surprisingly, participants burned more calories while sleep deprived, but ate more to make up for that fact.
"Sleep loss itself leads people to expend more energy because the body needs more to keep it awake," says Kenneth Wright, lead author of the report and director of the University of Colorado Sleep and Chronobiology Laboratory. "People eat more in response to these needs, but they eat more than they really need to, which leads to weight gain."
During a second week, participants were allowed nine hours of sleep a night. During that week, they consumed fewer carbohydrates and fat and lost weight.
Previous studies have linked lack of sleep with obesity, but most of those had been based on long-term surveys. Wright's experiment shows that just a few days of sleep deprivation leads to physiological changes in the brain and behavioral changes that lead people to eat more. His team had the ability to monitor participants 24 hours a day, and specially-designed rooms measured oxygen intake and carbon dioxide production, allowing him to determine participants' overall energy consumption and needs. All participants were "very healthy, well-screened volunteers" with no history of sleep problems.
Lack of sleep may have thrown off participants' internal clocks—while being sleep deprived, they tended to eat small breakfasts and ate meals and snacks well into the night.
"It changed the timing of their circadian rhythm—it was pushed to a later time, so people were eating more at night," he says. "On top of that, when people weren't obtaining enough sleep they ate smaller breakfasts because their bodies thought they were still supposed to be sleeping."