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Regularly staying up late at night and sleeping in the next day could put you at risk for gaining weight.

A new study finds that "late sleepers" tend to eat more, weigh more, and eat more low-quality food – even if they get roughly the same amount of sleep as people who hit the hay at a more normal time.

For the small study, which appears in the journal Obesity, scientists from Northwestern University looked at 51 adults: 23 late sleepers and 28 normal sleepers.

The participants recorded their eating and sleep habits in logs for at least seven days. They also wore a wrist actigraph, which monitors sleep and activity cycles.

Late sleepers went to sleep at an average time of 3:45 a.m. and woke up by 10:45 a.m. They ate breakfast at noon, lunch at 2:30 p.m., and dinner at 8:15 p.m. They also ate a "final meal" at 10 p.m.

Normal sleepers on average were up by 8 a.m., ate breakfast by 9 a.m., lunch at 1 p.m., dinner at 7 p.m., a late snack at 8:30 p.m. and were asleep by 12:30 a.m.

Both groups got roughly the same amount of sleep: 7 hours in the late sleep group, and 7.5 in the regular sleepers.

The researchers found that late sleepers took in 248 more calories a day, twice as much fast food and half as many fruits and vegetables as those with earlier sleep times. They also drank more full-calorie soft drinks.

Co-lead author Kelly Glazer Baron, a health psychologist and a neurology instructor at Northwestern University Feinberg School of Medicine, suggested those extra 248 calories can add up over time.

"The extra daily calories can mean a significant amount of weight gain – two pounds per month – if they are not balanced by more physical activity," she said in a news release.

Indeed, the late sleepers had an average higher body mass index, or BMI, than normal sleepers.

The study authors say that the calories that were taken in after dinner were the most problematic.

"Calories consumed after 8:00 p.m. predicted BMI after controlling for sleep timing and duration," they write.

Senior author Dr. Phyllis Zee, a professor of neurology and director of the Sleep and Circadian Rhythms Research Program at Feinberg and medical director of the Sleep Disorders Center at Feinberg and Northwestern Memorial Hospital says eating when the body expects to be sleeping may disturb our circadian rhythms.

"Human circadian rhythms in sleep and metabolism are synchronized to the daily rotation of the earth, so that when the sun goes down you are supposed to be sleeping, not eating," Zee said.

"When sleep and eating are not aligned with the body's internal clock, it can lead to changes in appetite and metabolism, which could lead to weight gain."

The research findings could be relevant to people who have trouble losing weight, suggesting that going to bed early could prevent overeating at night.

The findings also have relevance for night-shift workers, who eat at the "wrong" time of day related to their bodies' circadian rhythms.

"It's midnight, but they're eating lunch," Zee said. "Their risk for obesity as well as cardiovascular, cerebrovascular and gastrointestinal disorders is higher."

Northwestern researchers are now planning more studies to test the findings in a larger group. They also want to try to understand the biological mechanisms that link the relationship between circadian rhythms, sleep timing and metabolism.

The research was supported by the National Heart, Lung and Blood Institute of the National Institutes of Health.