German researchers at The University of Munich studied a phenomenon known as "social jet lag."  This can happen to people when they wake up at a specific time during the week and sleep in to a later time on the weekends.  Scientists studied people between the ages of 16 and 65.  They discovered that, along with age and gender, sleeping patterns can be a factor in body weight.  Experts suggest that people should try to maintain a regular sleeping schedule, because it will be good for your health in the long-run.