The rising number of Americans who are seriously overweight has triggered intense debate among scientists, advocacy groups, federal agencies, insurance companies and drug makers about whether obesity should be declared a "disease," a move that could open up insurance coverage to millions who need treatment for weight problems and could speed the approval of new diet drugs.

Proponents argue that new scientific understanding has clearly established that obesity is a discreet medical condition that independently affects health. Officially classifying obesity as a disease would have a profound impact by helping to destigmatize the condition, much as the classification of alcoholism as a disease made it easier for many alcoholics to get treatment, experts say. But equally important, the move would immediately remove key economic and regulatory hurdles to prevention and treatment, they say.

Opponents contend obesity is more akin to high cholesterol or cigarette smoking — a risk factor that predisposes someone to illness but is not an ailment in itself, such as lung cancer or heart disease. Labeling it a bona fide disease would divert scarce resources, distract public health efforts from the most effective countermeasures and unnecessarily medicalize the condition, they say.

Nevertheless, the move to classify obesity as a disease appears to be accelerating.

The Internal Revenue Service ruled last year that, for tax purposes, obesity is a disease, allowing Americans for the first time to claim a deduction for some health expenses related to obesity, just as they can for those related to heart disease, cancer, diabetes and other illnesses.

The federal agency in charge of Medicaid and Medicare is conducting a review to determine whether it, too, should consider obesity a disease. That would mean that for the first time the poor, elderly and infirm would be covered for some weight-control therapies without first having another illness diagnosed, such as diabetes. That decision would pressure private insurers to follow suit, and they are resisting the move.

The Food and Drug Administration is reviewing how it judges new weight-loss drugs. As part of that review, the agency will consider whether it should evaluate diet drugs more like it assesses treatments for such illnesses as diabetes and cardiovascular disease, which could help get new medications on the market more quickly by making it easier to get them approved.

"For ages, obesity has been regarded as a personal moral failing — a behavioral issue that’s easily fixed by people who have sufficient willpower to do so," said Morgan Downey, executive director of the American Obesity Association, a Washington-based advocacy group that has been lobbying for obesity to be reclassified. "The modern scientific understanding of obesity is that it is a complex disease in its own right."

That understanding has led many major medical authorities, including the National Institutes of Health and the World Health Organization, to conclude that obesity should be considered a distinct disease entity.

"There’s no question that obesity is a disease," said Arthur Frank, medical director of George Washington University’s Weight Management Program. "Obesity is a disease where there’s a disregulation of eating — just like diabetes is a disease where the system of controlling blood sugar is not functioning properly."

But not everyone agrees. Although obesity can increase the risk of a host of health problems, skeptics argue, so do smoking and high cholesterol, which are not considered diseases. Not everyone who is obese or overweight develops problems requiring treatment.

"You can be overweight and healthy if you are active," said Tim Church, medical director of the Cooper Institute in Dallas, a nonprofit research center focused on exercise. "In fact, an overweight individual who exercises is healthier than a normal-weight individual who is sedentary. You could say that if obesity is a disease, then not enough exercise is a disease or not eating right is a disease."