Opinion | Are We Thinking About Obesity All Wrong?

“Obesity is a disease,” Oprah Winfrey declared after disclosing her weight loss with an Ozempic-like drug.“It’s a brain disease,” a prominent obesity doctor explained on a “60 Minutes” episode about the drugs.

“Obesity is disease” even has its own discover page on TikTok.The American Medical Association and the World Health Organization share that view, but whether obesity should be considered a disease has been referred to by health experts as “one of the most polarizing topics in modern medicine.” Even Jens Juul Holst, a discoverer of the hormone that drugs like Ozempic mimic, told me he isn’t sure what to call obesity.“Whether it’s a disease in its own right is a very difficult question,” he said.

Finally, this dispute is coming to a head amid soaring demand for new weight loss medicines, as expert groups around the world rush to define what it means to have obesity.At the heart of the debate: The medical community has never provided a precise definition for obesity as a disease.It’s typically understood as an excess of body fat, using body mass index, or B.M.I., to gauge who has too much.

But B.M.I.— a person’s weight divided by the square of their height — was never meant to be used as a diagnostic tool and can’t determine whether someone is healthy or sick.

And there’s no consensus on the signs and symptoms that make obesity an illness the way high blood sugar levels are used to diagnose type 2 diabetes, or chest pain and irregular imaging to tell if someone has heart disease.Diagnosis by B.M.I.was always imprecise; in an era of remarkably effective weight loss drugs, it’s untenable.

Consider that 40 percent of American adults are classified as having obesity by having a B.M.I.of 30 or above.

With new treatments that cost upward of $1,000 per person per month, along with supply shortages, how to define obesity is more than just a fight over nomenclature.It’s about pinpointing who is sick and will benefit fro...