As people in the developing world stop dying of diseases of the poor, such as diarrhea, influenza, malaria, and measles, they have started dying of diseases of the rich instead. Obesity is climbing the rankings as a killer, but it has some way to catch up to global public-health enemy No. 1: tobacco. The only consumer product that kills if used as directed is a leading risk factor for every major noncommunicable disease: cancer, diabetes, respiratory illnesses, and cardiovascular conditions. And while smoking has declined in the U.S. and Europe, it’s on the rise in the developing world.