- Obesity puts people at risk for Type 2 diabetes, hypertension, heart disease and even some cancers.

- Scientists don't agree on whether obesity is a disease, itself, although research is suggesting it may qualify.

- The verdict could affect what health care providers cover.

With more than one-third of U.S. adults struggling to keep off the pounds, obesity has left its mark on Americans' waistlines and wallets.

Yet when the Institute of Medicine released its recommendations for essential health benefits to include in the Patient Protection and Affordable Care Act recently, the term obesity was nowhere in sight. The report helps Congress dictate what health insurance companies should cover when the act goes into effect.

Obesity didn't make the cut.

Ambiguity surrounding the condition's causes and a lack of evidence-based medical treatments are likely to blame. But given what researchers know -- and the costs associated with the condition -- should obesity be considered a disease? Should it gain some health care coverage from insurers?

A growing number of researchers think so.

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Typical definitions of disease include a change in a person's body that negatively affects its structure and function. Obesity not only causes structural changes in a person's fat tissue, but it also dictates how the body handles lipids, insulin and blood sugar. As a result, fat exists where it's not normally found in muscle, liver, cardiac tissue and the pancreas, interfering with organs' ability to work properly.

Jyme Schafer, director of medical and surgical services at the Office of Clinical Standards and Quality for the Centers for Medicare and Medicaid Services, told Discovery News that when it comes to providing health coverage for the Medicare population, the centers aren't in the position to view obesity as a stand-alone disease. Instead, the focus is on reducing obesity's role in other health problems.

"We recognize that [relieving obesity] improves health outcomes," Schafer said. "And that's the bottom line."

Currently, Medicare may cover weight loss surgery for some patients with obesity diagnosed alongside conditions such as Type 2 diabetes, and the centers plan to introduce a program focusing on ways to target obesity with behavior. The surgery remains one of the few interventions that insurance companies may cover, even for other people not on Medicare, though policies can vary by state.

Is having a big gut a form of disease? The answer could affect health care policies.iStockPhoto

Rather than being worthy of coverage in its own right, obesity often gets consideration only when it coincides with other conditions.

Despite the debate surrounding obesity's label, genetic studies look deeper than the "calories in, calories out" mantra.

"The evidence is very clear there is a genetic component to the risk of becoming obese," said Claude Bouchard, a professor and researcher in genetics and nutrition at the Pennington Biomedical Research Center in Baton Rouge, La. "And this genetic component is stronger for severe obesity than it is for milder forms of obesity or being overweight."

Years of family and twin studies have singled out 32 genes influential to obesity. But the condition usually isn't a "one-gene affair," he said. Because people receive two variants of genes -- one from mom and another from dad, that leaves 64 possibilities for a genetic predisposition to obesity.

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But there are a few exceptions, mostly extreme cases of the health problem, where no matter what people do or eat, they become obese. This can be attributed to a single genetic mutation, Bouchard said. A similar phenomenon has been observed in other animals, including primates and rodents, despite individuals eating similar diets and having the same activity levels as other members in their groups.

Still, where do sedentary lifestyles and "obesogenic," Super-Size-Me environments come into play?

Environment plays a role, but it's unclear exactly how it interacts with a person's genetics. In fact, Bouchard said epigenetics, or measuring what changes gene expression, is the mysterious frontier of obesity research.

Until scientists can piece together nature's effects on nurture, it will be tough to be sure what exactly causes obesity -- and even more difficult to create medical interventions to include into health care policy.

Refusing to treat obesity like other metabolic diseases seems prejudiced, Bouchard said.

"When we put obesity in another category, I always feel it is purely a consequence of looking at it from a discriminatory point of view," he said.

Some people may think that calling obesity a disease rids people of personal responsibility to watch their weight. Other research suggests that people who cannot properly produce a compound called leptin are more likely to become obese, too, said Judith Stern, a distinguished professor of nutrition at the University of California-Davis. Other theories put forth that viruses or infections might factor into a person's risk.

Above all, she said, obesity patients -- especially those who have tried everything -- need consistent treatment and support.

"We're stacking the decks against obese people," she said. "I think it will take many years to turn this around."