On June 18, the American Medical Association voted to officially declare obesity a disease, rendering more than one-third of American adults afflicted.

The AMA was only the latest in a long list of medical organizations that has debated exactly how obesity should be approached.

In 2008, the Obesity Society issued official support for labeling it a disease after commissioning a panel of experts to examine the issue. The International Classification of Diseases, a health care classification system published by the World Health Organization, lists several categories of obesity, among them "drug-induced obesity" and "obesity due to excess calories."

"Recognizing obesity as a disease will help change the way the medical community tackles this complex issue that affects approximately one in three Americans," AMA board member Dr. Patrice Harris said in a statement.

Proponents of calling obesity a disease hope the definition will encourage physicians to take the condition more seriously and pressure insurance companies to cover more treatments such as counseling, obesity drugs and, in extreme scenarios, surgeries.

But opponents of the classification have said the move risks further stigmatizing an already stigmatized population or encouraging a medical response to a problem that is best combated by lifestyle changes. "I'm concerned about the health ramifications of this decision. Weight bias is much more health-damaging than carrying a lot of body fat," said Linda Bacon, a professor of nutrition at City College of San Francisco and author of the book "Health at Every Size: The Surprising Truth About Your Weight."

"Extensive research establishes that some people in the 'obese' category live long, healthy, disease-free lives — proving that 'obesity' itself is not a sole determinant of disease," she said.

The AMA's vote was approved by the group's policymaking House of Delegates after its own Council on Science and Public Health concluded in a report that calling obesity a disease was problematic. It reasoned that since obesity lacked a clear definition or good form of measurement, it was difficult to categorize it as a disease.

"Most people have additional fat, but that additional fat may or may not be causing metabolic risk," said Dr. Patricia Crawford, director of the Center for Weight and Health at Berkeley. Some people may have a BMI well over 30, for example, but have no health problems. In other words, some people could have what the AMA now calls a disease without any clear expression of it.

At Children's Hospital Oakland, Dr. Lydia Tinajero-Deck said obesity has already long been managed as a disease.

"Obesity doesn't go away; it's sort of a lifelong management," said Tinajero-Deck, co-director of the Healthy Hearts programs, which helps kids with weight management. "We see more and more kids weigh over 200 pounds, and they do not look well and they do not feel well."