Weight-loss experts have a novel prescription for people who want to shed pounds: Get some sleep. Those who got less than four hours of sleep a night were 73 percent more likely to be obese than those who got the recommended seven to nine hours of rest, scientists discovered. Those who averaged five hours of sleep had 50 percent greater risk, and those who got six hours had 23 percent more. Sleep deprivation lowers leptin, a blood protein that suppresses appetite and seems to affect how the brain senses when the body has had enough food. Sleep deprivation also raises levels of grehlin, a substance that makes people want to eat.