From Science:
When we eat may be just as important as what we eat. A new study shows that mice that eat when they should be sleeping gain more weight than mice that eat at normal hours. Another study sheds light on why we pack on the pounds in the first place. Whether these studies translate into therapies that help humans beat obesity remains to be seen, but they give scientists clues about the myriad factors that they must take into account. Observations of overnight workers have shown that eating at night disrupts metabolism and the hormones that signal we're sated. But no one had done controlled studies on this connection until now. Biologist Fred Turek of Northwestern University in Evanston, Illinois, and graduate student Deanna Arble examined the link between a high-fat diet and what time of day mice eat. A control group of six nocturnal mice ate their pellets (60% fat by calories, mostly lard) during the night. Another group of six ate the same meal during the day, Turek says, which disrupts their circadian rhythm–the body's normal 24-hour cycle.
After 6 weeks, the off-schedule mice weighed almost 20% more than the controls, Turek and Arble report today in Obesity, supporting the idea that consuming calories when you should be sleeping is harmful.
More here.