In late September, millions of Americans tuned in to an episode of the popular situation comedy Parks and Recreation in which a pragmatic city politician tried to limit the sale of large sodas in an effort to fight obesity. The story included gags like a 64 fluid ounce (2 L) drink known as the “Sweetums Sugar Splash,” and a 512 ounce “child size” option—so called because, as a soda representative smilingly puts it, “It’s roughly the size of a 2 year old child, if the child were liquefied.”

The episode represented a milestone in the ongoing debate about soda and obesity. For years, the topic had lingered in research laboratories and academic journals; today, it is international news, showing up on primetime television and being discussed by the mayor of London, Boris Johnson. It is a transformation prompted in large part by a controversial proposal from Michael R Bloomberg, the billionaire mayor of New York City.

This spring, Bloomberg introduced a plan that would ban the sale of supersized sweet drinks in New York’s restaurants, movie theaters, street carts, and sports stadiums. Sugary drinks, defined as having 25 kilocalories per 8 ounces (250 mL), would be available only in quantities below 16 ounces—smaller than a typical vending machine bottle. The rule would affect a range of popular beverages like sport drinks and pre-sweetened iced teas.

Bloomberg’s plan was approved in September by the city’s Board of Health, whose members are appointed by the mayor, and it will go into effect in March. Many public health organizations praised the plan, but it has also spurred uneasiness among consumers and significant opposition from the soft drink industry, which spent more than …