Are you an early bird or a night owl? Being the latter can lead to an additional 2 pounds a month weight gain, according to a new Northwestern Medicine study, which showed that people who stay up late at night eat more calories, have more unhealthy diets and are more likely to have a higher body mass index.

Northwestern University scientists examined 52 adults on their dietary patterns by dividing subjects into normal sleepers (who go to bed by 12:30am and wake up by 8am) versus late sleepers (whose bedtime average at 3:45am and wake up by 10:45am).

Compared to normal sleepers, late sleepers:

• Consumed 248 more calories a day
• Ate twice as much fast food
• Ate half as many fruits and vegetables
• Drank more full-calorie sodas
• Have a higher body mass index (BMI), a measure of body weight

The late sleepers consumed the extra calories during dinner and later in the evening, though the researchers are unsure whether it's because late sleepers prefer more high-calorie foods or because there are less healthy options at night.

Nevertheless, the sleep-weight connection is clear: "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," says senior author Phyllis Zee, M.D.