Dr. Shawn Garber, a New York physician who has performed more than 3,500 laparoscopic gastric bypasses and more than 3,000 Lap-Band procedures, said insurers would be wise to start willingly covering such treatments without them being deemed medically necessary because of the long-term savings from having fewer obese people to treat for associated conditions.
"I think that in the long term, they're definitively going to save," Garber said. "But most insurance companies don't look in the long term."
In addition to the potential for more insurance coverage of obesity-related surgery, the AMA's resolution could fuel already increasing interest in developing medication for obesity itself, an area that had long languished among pharmaceutical companies.
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"This decision might change decisions to cover the drugs related to obesity," said Paul Fronstin of the Employee Benefit Research Institute. "It could give pharmaceutical companies more incentive to start investing money in obesity-related drugs if they think that coverage for those drugs are going to increase."
Dave Fox, a lawyer who specializes in new drug regulation at the firm Hogan Lovells, said the AMA's move is "a strong message from a credible source" that could "pressure" the Food and Drug Administration to focus more on the benefits of a potential new drug than on the risks, as it considers drugs for approval.
Fox noted that the AMA's announcement comes as two new drugs targeting obesity—Belviq by Arena Pharmaceuticals and Qsymia by Vivus—have begun sales recently.
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Before that, he said, "We had a tremendous deficit, lag or delay in the development of obesity drugs." He added, weight loss drugs in the past have had the potential to increase the risk of cardiovascular conditions.
"There's always worry that the cure is worse than the disease," said Fox, who formerly worked for the FDA as associate chief counsel for drugs.
While noting the AMA's disease classification of obesity doesn't technically change the FDA's approach to approval of new drugs, Fox said it's symbolically important in the context of "the positive momentum that's been generated in the past couple of years of approval of some weight-management drugs."
"The FDA has to weigh benefits against risks, and you're hearing from a voice in the community that is saying treating obesity as a disease is itself a benefit," Fox said. "That's how things change over time in government."
—By CNBC's Dan Mangan and Bertha Coombs. Follow them on Twitter