WebMD is reporting on a study showing that sleep may help weight loss. Apparently, the hormone leptin — which regulates appetite — was found depressed in those who had less sleep:
Leptin is a hormone that is made predominately in fat cells. The amount of leptin in the blood is proportional to the amount of body fat. It is thought to decrease appetite. However, most obesity is characterized by resistance to leptin and its appetite-suppressing effect.
Participants who reported less sleep tended to have lower leptin levels than predicted. That might mean that their bodies weren't using leptin very efficiently. […]
The article goes on to say that it’s not as simple as More Sleep → Lose Weight, since there’re many factors that go into weight gain vs weight loss. Still, there’s nothing to lose (well, other than weight) by getting more sleep.