In 2002, a dynamic doctor named Thomas Frieden became health commissioner of New York City. With support from the new mayor, billionaire Michael Bloomberg, Frieden and his health department team prohibited smoking in bars, outlawed trans fats in restaurants, and attempted to cap the size of sodas, among other groundbreaking actions. The initiatives drew heated criticism, but they worked: by 2011, 450,000 people had quit smoking, childhood obesity...