If your nighttime routine includes a super-late bedtime, you may be at risk for some extra weight gain, according to a new study. The likely culprit? Late-night snacks.
Researchers from the University of Pennsylvania found that in a controlled laboratory setting, people who were restricted from getting any more than four hours of sleep for five nights in a row tended to consume more calories, and gained more weight than those who were allowed to sleep 10 hours a night.
"Although previous epidemiological studies have suggested an association between short sleep duration and weight gain/obesity, we were surprised to observe significant weight gain during an in-laboratory study," study researcher Andrea Spaeth, a doctoral candidate in the psychology department at the university, said in a statement.
The study, published in the journal SLEEP, included 225 healthy, non-obese people, who were between ages 22 and 50 and spent as many as 18 days in a row in a sleep lab. Researchers assigned some of them to sleep from 10 p.m. to 8 a.m., while others were assigned sleep deprivation, where they only slept from 4 a.m. to 8 a.m. for five nights in a row. All the study participants were fed meals at set times of the day, but they were also given access to snacks from the lab kitchen if they wanted to eat at other times of the day; no exercise was permitted.
Researchers found that those who were sleep-restricted for five nights gained about two pounds, compared with those who slept for 10 hours a night, who gained about a quarter-pound, News@JAMA reported. Men also gained more weight than women, and African Americans gained more weight than Caucasians, in association with the sleep deprivation.
Researchers also found that those who were sleep deprived consumed more calories (including a greater proportion of calories from fat) in general because they were eating during the late-night hours.
"Sleep-restricted subjects consumed an excessive amount of calories beyond daily caloric requirements during days with a delayed bedtime compared with control subjects who consumed an adequate amount of calories during corresponding days," researchers wrote in the study. "Thus, increases in caloric intake in sleep-restricted subjects were not due to novelty of the laboratory setting or other environmental factors."
Interestingly, researchers found that the sleep-deprived participants didn't increase their carbohydrate intake and instead had a regular proportion of protein, fat and carbohydrates, showing that "subjects did not over-consume a specific macronutrient at the expense of the other two macronutrients during sleep restriction," they wrote.
This isn't the only research to show that weight gain can come from sleep deprivation because of added calories. A controlled sleep study conducted by researchers at the University of Colorado Denver's Anschutz Medical Campus also showed that people tended to eat more in after-dinner snacks if they were sleep deprived (meaning they got fewer than five hours a night) for a week.
And just recently, a study presented at the meeting of The Endocrine Society this summer showed that sleep deprivation seems to prompt higher levels of a particular molecule in the blood -- one that is responsible for the feelings of reward and enjoyment that come from eating.