Results of a study exploring the relationship between sleep habits, dietary behavior, and body-mass index have shown that people who habitually stay up late at night and sleep in late the next day are more likely to weigh more than people who go to sleep earlier and get up earlier. Researchers at Northwestern University studied 51 people (23 late sleepers and 28 normal sleepers) with an average age of 30. Those deemed as late sleepers went to sleep at an average time of 3:45 AM, and got up by 10:45 AM. While normal sleepers went to sleep at an average time of 12:30 AM, and got up by 8 AM. Results showed that late sleepers had shorter sleep duration and later meal times. They also consumed 248 more calories a day, consumed more calories after 8:00 PM, drank more full-calorie sodas, and ate twice as much fast food and half as many fruits and vegetables as normal sleepers. Late sleepers also had a higher body-mass index than normal sleepers. Co-lead author Kelly Glazer Baron warned that the extra daily calories consumed by late sleepers can lead to a significant amount of weight gain of approximately two pounds per month, if those calories are not offset by more physical activity. Results also showed that calories consumed after 8:00 PM predicted body-mass index, even after controlling for sleep timing and duration. This finding led the authors to conclude that caloric intake after 8:00 PM may increase the risk of obesity.
