If you’re overweight, don’t sleep well and lack energy during the day, losing a few pounds might help fix all that. It worked for obese mice. Researchers at the Perelman School of Medicine at the University of Pennsylvania fed half the mice in their study regular mouse chow and the other half chow with more than three times more fat. After 8 weeks some of the mice in each group were switched to the opposite diet. Not surprisingly, those that had been on the high fat diet lost weight while those that had been eating regular mouse chow gained. After the ninth week, the mice on the high fat diet weighed 30 percent more than the other mice, slept an hour longer per day and were more likely to fall asleep during the day. However, the “diet switch” mice in both groups had completely different sleep/wake profiles, leading the researchers to conclude that changes in body weight are a key factor in regulating sleep. If you're overweight and feel tired during the day, losing only a small amount weight may result in better sleep and less daytime fatigue, the researchers reported. Will what works in mice really help humans sleep better? Stay tuned.