A new study from the Mayo Clinic reveals that getting just four hours of sleep a night (or less) leads to weight gain and an increase in belly fat – even for young, healthy, and average weight people. That belly, or visceral fat, is the dangerous kind – which surrounds organs and can cause a host of health problems. And making up sleep on the weekends doesn’t count. Researchers found that sleeping in on the weekends had no effect on the accumulation of visceral fat.