But being obese is a higher BMI than overweight, and the bar is actually quite low. Lower than most people think. A lot of people think they're overweight, but they're not, they're obese.
Health risks of being overweight are very well researched and are significant (cancer risk, type 2 diabetes, cardiovascular health). If you meant the mortality, then it is also worse for overweight people when confounding for smoking and reverse causality.