In the online edition of the journal Obesity is a study about late night eating habits. Psychologists studied 51 people, 23 late sleepers (average bedtime 3:45 a.m.) and 28 normal sleepers (average bedtime 12:30 a.m.). Study participants recorded their eating and sleeping in logs and had objective sleep measurements with wrist actigraphy.
Late sleepers ate 248 more calories per day, ate twice as much fast food, ate half as many fruits and vegetables, and drank more full-caloire soda than the participants with normal sleep times. The late sleeepers consumed the extra calories during dinner and later in the evening when everyone else was asleep. Left unchecked, this amount of extra calories could lead to a 2 pound weight gain per month!
The study researchers don't know if the late sleepers consume the extra calories beacuse they prefer more high-calorie foods or because there are less healthful options late at night. It could also be that there is a circadian effect, meaning that staying awake later than normal could lead to hormone changes that affect metabolism and appetite. This, in part, could explain the fact that people who work third shift have increase risk of obesity, cardiovascular, and gastrointestinal disorders.