Sleeping in won’t make you fat. In fact, a new study shows that more hours in the sack could help you slim down by reducing how much control your genes have on your weight. The study, published in the journal Sleep, looked at the sleep patterns and body mass index (BMI) of over 1,000 twins. On average, the people in the study slept 7.2 hours a night, which falls within the National Sleep Foundation’s recommended seven to nine hours. People who slept less than seven hours a night, however, had a higher BMI than those who slept more than nine hours. Genetics also had a greater influence on the BMI of the short sleepers, with 70 percent of their body weight controlled by genes, compared to 32 percent for the long sleepers.
Body weight is shaped by many factors—both genetic and environmental—that combine to determine how much you weigh. Previous studies have shown that genes can influence weight by controlling many of your body’s functions, such as glucose metabolism, energy use, storage of fatty acids, and feeling full. By affecting those genes, sleep can also alter weight. "The less sleep you get, the more your genes contribute to how much you weigh. The more sleep you get, the less your genes determine how much you weigh," Dr. Nathaniel Watson, one of the study’s authors, told USA Today. Is it possible to sleep the pounds off? Not quite. Sleeping more than nine hours a night, though, can reduce the influence of your genes on your weight. That gives more power to environmental factors—like diet and exercise—things that you can consciously control. And if you're not sleeping well, try working out. You'll get a good night's rest and lose even more weight.