MONDAY, May 9 (HealthDay News) -- Night owls who consistently stay up late may be putting themselves at higher odds for weight gain, a new study finds.

Researchers at Northwestern University in Chicago found that people who burn the midnight oil typically consume more calories in the evening and eat more fast food than "early to bed, early to rise" types.

The study, published online in the journal Obesity, examined 51 people averaging 30 years of age. Twenty-three typically went to bed by about 3:45 a.m. and woke up by 10:45 a.m. The rest, considered normal sleepers, were in bed by 12:30 a.m. and up by 8 a.m.

The researchers found that people who stayed up late consumed an average 248 more calories daily. The diet of the night owls also included twice as much fast food, more non-diet sodas and only half as many fruits and vegetables as those with earlier sleep times. These extra calories were typically consumed at dinner and later in the evening. The study also found that those who regularly stayed up late had a higher body mass index than normal sleepers.

"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," the study's co-lead author, Kelly Glazer Baron, a health psychologist and a neurology instructor at Northwestern University Feinberg School of Medicine, said in a university news release.

The researchers suggest the reason behind the weight gain may be that healthier foods are not readily available at night, or that night owls tend to prefer foods that are higher in calories. The study concludes that eating habits are linked to sleeping patterns, and that when you eat may be just as important as what you eat.

"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," the study's senior author Dr. Phyllis Zee, 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, said in the news release. "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 study's authors also pointed out that people who eat unhealthy foods at the wrong time of day may increase their risk of stroke, heart disease and gastrointestinal disorders.

More information

The U.S. Centers for Disease Control and Prevention offers detailed information about the causes and dangers associated with obesity.