Just two weeks of sleeping 4 hours a night increased visceral fat by 11% in healthy young men, with almost no change on the scale In other words, they were accumulating harmful visceral fat (the deep, inflammatory fat stored around your organs) even though body weight barely moved Mechanistically, even one night of short sleep can cause acute insulin resistance, while repeated sleep loss raises cortisol, cravings for high-energy foods, and calorie intake The result is a metabolic setup that makes visceral fat accumulation much more likely over time