Adding to evidence that sleep plays a role in weight regulation, a recent US study found that sleeping too little can hamper(阻止する、妨げる)weight loss. The study involved 10 overweight men and women, all of whom followed the same calorie-restricted diet. Regardless of whether they were receiving 8.5 or 5.5 hours of sleep per night, the participants lost the same amount of weight - nearly seven pounds on average. However, when they were limited to just 5.5 hours of sleep a night, participants mainly lost muscle as opposed to fat and reported feeling more hunger during the day.