A study in the July issue of Sleep suggests that healthy adults with late bedtimes and chronic sleep restriction may be more susceptible to weight gain due to the increased consumption of calories during late-night hours. In the largest, most diverse healthy sample studied to date under controlled laboratory conditions, results show that sleep-restricted subjects who spent only four hours in bed from 4 a.m. to 8 a.m. for five consecutive nights gained more weight than control subjects who were in bed for 10 hours each night from 10 p.m. to 8 a.m.  Participants in the restricted sleep group consumed an average of 553 additional calories during late-night hours, which is the equivalent of a Big Mac, notes the NPR Shots blog.