In a new study, Northwestern sleep researchers say late sleepers consumed 248 more calories a day. They also ate twice as much fast food and half as many fruits and vegetables.
If not balanced with physical activity, experts say, this can translate into weight gain of about 2 pounds per month.
What's not known is whether night owls consume the extra calories because they prefer these foods or because there are less healthful options at night.
The study is now online in the journal Obesity.