In the US, there are very few diseases that will automatically qualify a person for disability. To prove any disease or disorder is a disability, one must show that it prevents the sufferer from any kind of substantial gainful activity, and that it is expected to last more than a year or end in death. It is extremely difficult to prove that any condition is severe enough to meet the requirements. Obesity is a disease, but it is considered curable/treatable, and many obese people have jobs. To give another example, alcoholism is a disease but is not a disability for purposes of insurance or social security payments.
The difference this will make is that insurance companies will be encouraged to cover treatments for obesity. For example, reimbursing membership in weight loss programs, or even gym memberships and exercise classes, or coverage for prescription drugs that treat obesity. Currently, weight loss treatments like the lap band require a co-morbid disorder (diabetes, for example) in order to be covered by most insurance plans.
I don't know that there is an agenda by the AMA, although I would be interested in hearing everyone's ideas about what the agenda might be. I see this is a good thing for consumers who may have more options under their insurance plans. If the cause of one's obesity is Cushing's, it makes no difference because Cushing's is already a disease (and not a disability according to SSA) and "obesity treatments" are not going to help someone with Cushing's, either, so for us on this forum, it is probably not going to affect us either way. One fear I have, however, is that people like me, who did not seem to have "classic Cushing's" may have been pushed into unnecessary and invasive procedures. I always knew that my weight was NOT due to overeating or lack of exercise, but I was not able to convince my doctor's of that.
Personally, I tend to think that obesity is assumed to be the cause of disease, rather than the symptom, far too often.