More likely the problem is that when people get up at 1am and have a snack they aren't generally going to be in the mood for a salad. They're far more likely to get oreos and milk or a bowl of ice cream or some chips and salsa or whatnot. Adding an extra 500 calories of unhealthy food outside your three meals per day every couple of nights is going to add weight, same as if you had it with dinner or at 4pm.