Mortality-wise, no, they're in comparable risk of death. Disease-wise, however, the obeast is under higher risk. The problem about being underweight is that diseases that usually go away can potentially kill you. A simple flu might be enough because your body isn't strong enough to fight the virus. On the other hand, obese patients are always sick, but their bodies are better at handling the outcomes. Many of them live with diabetes, high blood pressure, sleep apnea, and clogged arteries for decades before finally dying.