The new decision was made at the AMA's annual meeting on Tuesday by delegates in Chicago, and went against a recommendation by a committee that had studied the subject.
Dr. Patrice Harris, a member of the association's board commented in a statement, "Recognizing obesity as a disease will help change the way the medical community tackles this complex issue that affects approximately one in three Americans."
The change will aide in the fight against obesity-related diseases such as type 2 diabetes and heart disease, and could improve funding for obesity drugs, surgery, and counseling.
Whether obesity should be labeled as a disease has been historically debated. In 2008, the Obesity Society officially announced their support for calling obesity a disease.
In 2004, Medicare took away wording from its coverage manual that previously said obesity was not a disease, and the Internal Revenue Service has said obesity treatments can count for tax deductions.
The current vote of the AMA House of Delegates countered the conclusions of the association's Council on Science and Public Health, which had examined the subject over the last year.
The council declared that obesity should not be classified as a disease because the measure that is used to categorize obesity (body mass index, BMI) is flawed. Separate studies suggest that BMI does not measure your overall fat or lean tissue (muscle) content.
Many people who have a BMI higher than the level that is considered obese are healthy, while others below it can have metabolic issues and dangerous body fat levels.
The council said:
"Given the existing limitations of B.M.I. to diagnose obesity in clinical practice, it is unclear that recognizing obesity as a disease, as opposed to a 'condition' or 'disorder,' will result in improved health outcomes."
A reason the AMA decided in favor of obesity as a disease is that it will decrease the stigma of obesity that comes from the widespread thought that it is just the outcome of excessive eating and not enough exercise. Doctors say some people do not have complete control of their weight.
Additionally, the Council recognizes that obesity fits some medical criteria of a disease, like impairing body function.
Those who did not agree with the change of classification cited that making obesity a disease would categorize one-third of Americans as being sick and may lead to more medication and surgeries that are expensive, instead of lifestyle changes.
The delegates declined the conclusion of the study council and voted in favor of the resolution that was also supported by the American College of Cardiology and the American Association of Clinical Endocrinologists.
The resolution read:
"The suggestion that obesity is not a disease but rather a consequence of a chosen lifestyle exemplified by overeating and/or inactivity is equivalent to suggesting that lung cancer is not a disease because it was brought about by individual choice to smoke cigarettes."
According to a report by the Robert Wood Johnson Foundation and Trust for America's Health published in August, obesity rates in America have remained steady for the first time since 1980.