Sleep aids in weight loss, especially loss of fat

Scientific American Blog - Sleep might help dieters shed more fat

This study adds to the salubrious effects of getting enough sleep by showing the kind of weight lost by dieters. Researchers compared the same dieters who got a full night's sleep (7.5 hrs) compared to a truncated sleep schedule (5.5 hrs). The diet was reduced caloric intake that wasn't coupled with exercise. While the dieters lost the same amount of weight under both regimens, those with a full night's sleep lost 55% more fat than the others. The shortened sleep schedule group lost more "fat-free body mass", including water and muscle, and also reported being hungry more of the time. Researchers looked for a hormone ghrelin that supposedly stimulates hunger and also lowers energy use in the body (influencing metabolism) and found that in the sleep-deprived, ghrelin levels were higher. If it hadn't been for the tight caloric controls imposed by the study, the sleep-deprived might have eaten more and not even lost the weight they did.