Sleep schedules and the amount of sleep a person gets appear to be very connected to weight. People who go to sleep later and wake up later are much more likely to be overweight. In one Australian study, older children and teens who went to sleep late and woke up late were about 1.5 times more likely to be obese than kids who had other sleep schedules, and a study from Northwestern University showed that those who sleep later consume about 250 more calories per day than those who sleep earlier. The Northwestern study showed that late sleepers also ate about half the fruits and vegetables of early sleepers and twice the fast food of early sleepers.
More facts about sleep and weight:
Missing sleep increases the secretion of ghrelin, a hormone that stimulates appetite, and it decreases secretions of leptin, a hormone that makes people feel full. This, combined with a variety of other factors, is likely connected to weight gain in people who get inadequate amounts of sleep.
People who work night shifts are much more likely to be obese, have heart problems and gastrointestinal disorders, even if they sleep the same amount of time as others.
Another reason early risers might be less likely to become obese is that they are much more likely to exercise during the day.