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On a cool June afternoon in 2013, hundreds of doctors from around the country streamed into the grand ballroom of the Hyatt Regency Chicago. They were there, on day three of the American Medical Association’s annual meeting, to vote on a list of organization policies—boring but necessary stuff, for the most part. But one item on the ballot that day would prove contentious, and not just within the paneled walls of the ballroom. Resolution 420 was short and to the point: “That our American Medical Association recognize obesity as a disease state with multiple pathophysiological aspects requiring a range of interventions to advance obesity treatment and prevention.”

The question—whether to classify obesity as a disease in and of itself, or continue to consider it a risk factor for diseases like type 2 diabetes—had been under discussion for years, both within the organization and outside it. Months earlier, the AMA asked its own Committee on Science and Public Health to explore the issue; the committee came up with a five-page opinion suggesting that obesity should not be officially labeled as a disease, for several reasons.

For one thing, the committee said, obesity doesn’t fit the definition of a medical disease. It has no symptoms, and it’s not always harmful—in fact, for some people in some circumstances, it’s been known to be protective rather than destructive.

For another, a disease, by definition, involves the body’s normal functioning gone wrong. But many experts think obesity—the body efficiently storing calories as fat—is a normal adaptation to a set of circumstances (periods of famine) that’s held true for much of human history. In that case, the bodies that tend toward obesity aren’t diseased; they’re actually more efficient than naturally lean bodies. True, we live in a time when food is more abundant for most people and life is more sedentary than it used to be, and we don’t have the same need to store fat. But that simply means the environment has changed faster than we can adapt.

Finally, the committee worried that medicalizing obesity could potentially hurt patients, creating even more stigma around weight and pushing people into unnecessary—and ultimately useless—“treatments.”

The AMA membership didn’t agree with the committee; they passed Resolution 420 in an overwhelming voice vote. I asked the organization’s president, Ardis Hoven, an internist who specializes in infectious diseases, to help me understand why the membership voted that way despite the committee’s recommendation. She wouldn’t talk to me directly, instead writing through a spokesperson, “The AMA has long recognized obesity as a major public-health concern, but the recent policy adopted in June marks the first time we’ve recognized obesity as a disease due to the prevalence and seriousness of obesity.”