A long-term Nurses Health Study of middle-aged women reports that too little sleep can lead to weight gain. They found that women who slept only five hours or less each night were 32 percent more likely to gain at least 33 pounds during the 16 years of the study, compared with those who averaged at least  seven hours of shut-eye. The study could not correlate the weight gain to diet or exercise habits. Scientists suspect decreased sleep modifies the metabolism or that perhaps fewer calories are burned during the day because the subject was too tired to “fidget.”