The question mark at the end of the title is there not so much because I’m questioning whether obesity is a disease but because I wonder why anyone thinks it’s useful to say so.

At the recent annual meeting of the American Medical Association, our nation’s largest organization of doctors, the House of Delegates adopted a resolution calling for the AMA to “recognize obesity as a disease state with multiple pathophysiological aspects requiring a range of interventions to advance obesity treatment and prevention.”

By and large we have thought of obesity as a risk factor for other diseases rather than a disease in its own right. So the obese are more likely to have abnormal levels of lipids in the blood (cholesterol, triglycerides) and to have adult-onset diabetes. That makes obesity indirectly a contributor to cardiovascular disease, including heart attacks and strokes.

It helps to have a definition. The definition we use is based on body mass index (BMI), which is an imperfect but mostly workable measurement of whether a person’s weight is in a desirable range. It is calculated from height and weight. If your BMI is higher than 25, you’re considered overweight. Once it reaches 30, you’re obese.

The reason it’s imperfect is that some people with relatively large muscle mass may be quite fit and healthy, and have a percent body fat that is low enough to be enviable, yet have a BMI that is higher than “desirable.” That is because muscle is denser than fat, and so it contributes more to body weight. Take two people of the same weight. The one with more muscle and less fat takes up less space; his/her body has less volume. That person is thinner, trimmer, and (all other things being equal) healthier. So if you’re muscular and have a relatively low percent body fat, your BMI may falsely suggest you are overweight or even obese.

There are many online calculators, such as the one found here: http://www.nhlbi.nih.gov/guidelines/obesity/BMI/bmicalc.htm.

Knowing, then, that obesity puts one at risk for serious health problems, why does it matter if we call it a disease rather than an important risk factor for disease? Well, the supporters of the AMA resolution think it places more emphasis on the importance of helping people (patients) do something about it. They hope that it will cause health insurers to be more likely to pay for interventions that doctors can offer to patients.