Is obesity really a disease?

Last month, the American Medical Association classified obesity as a disease in its own right for the first time. (Previously, it had been categorized as a symptom or risk factor.)  There is plenty of evidence that shows people who are obese are more likely to develop diabetes and cardiovascular disease. But does that make obesity a disease in its own right? What about being overweight, but not obese?

It turns out, there is a substantial body of evidence that shows being overweight or slightly obese is not as harmful as most of us might believe.

Before we dive into the data, let’s review that obesity is determined by a measure called Body Mass Index, or BMI, a calculation of body mass in relationship to height. (As a side note, AMA’s Council on Science and Public Health studied the obesity issue for the past year and concluded obesity should not be considered a disease mainly because BMI is a simplistic and flawed measurement.)

 A systematic review published in the Journal of the American Medical Association earlier this year found that individuals who are slightly obese or simply overweight are equally as healthy or healthier compared to those who maintain a normal weight. The review included 97 studies which involved more than 2.8 million participants.

It determined that people classified as simply overweight – with a BMI of 25 to 30 – had significantly lower mortality rate compared with normal weight participants. Those classified with Grade 1 obesity – with a BMI of 30 to 35 – had the same mortality rate as normal weight individuals. Only those with a BMI of more than 35 have a higher mortality rate.

In addition, two other reviews published in 2009 and 2013 examined whether losing weight helped extend the life of people who were overweight and obese. Both found little evidence that losing weight helps prolong life.

The reviews did find that people with obesity-related risk factors, such as diabetes or cardiovascular disease, fared better if they lost weight. They also found evidence for improved quality of life in obese individuals who lose weight. But obese people who were otherwise healthy did not prolong their lives simply by losing weight. In fact, the safest body-size trajectory was stable weight while improving physical fitness.

What’s the take home message?  For people who are extremely overweight or suffering from obesity-related diseases, it’s important to lose weight. For those who are moderately overweight, focusing on eating healthy foods and improving physical fitness is more important than actual weight loss.