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How Obesity Matters More Than BMI

A new study and commentary in the Annals of Internal Medicine once again points to the fact that obesity — the unhealthy accumulation of adipose tissue — matters much more than BMI. Karine Sahakyan and colleagues analyzed the risk of death in people with obesity defined only by a BMI over 30 to the risk for people with excess abdominal fat at a BMI less than 25. They found a higher risk of death for people with “normal-weight obesity” than for people with a BMI over 30.

Speaking for the Obesity Society, psychologist Martin Binks explains:

If you just look at BMI, you’re not getting the whole picture. If someone has 50 pounds of body fat spread all over their body, they have a very different risk profile than if the fat is all in their stomach.

Binks is an associate professor of nutritional sciences at Texas Tech University and was not involved in the study. In the editorial that accompanies the study, Paul Poirier of Université Laval in Montreal says:

Although the utility of BMI has been borne out in epidemiologic studies, there are limitations to using BMI alone to assess adiposity in clinical practice. The numerator in the BMI calculation is total body weight and does not distinguish between lean and fat mass. The long-term deleterious consequences of excess adiposity are marked and important. These new data provide evidence that clinicians should look beyond BMI.

This is yet another reminder that obesity is not defined by BMI any more than an infection is defined by fever. Both BMI and body temperature are useful numbers and nothing more. Clinical diagnosis takes more than a single number.

Obesity is defined by the unhealthy accumulation of fat tissue.

Click here for the study, here for the commentary, and here to read more from Medscape.

Numbers 17 18, photograph © namtaf / flickr

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November 13, 2015

6 Responses to “How Obesity Matters More Than BMI”

  1. November 13, 2015 at 6:26 am, Angela Meadows said:

    We’ve known for years that BMI is not an adequate measure of health (or actually a measure of health at all), and evidence continues to mount. And yet, obesity IS defined by BMI. When are we going to get to the point that everybody with a BMI over 30 is not automatically considered a walking disease?

  2. November 13, 2015 at 6:36 am, Ted said:

    Actually, Angela, obesity is not defined by BMI for anyone who understands the disease. Though you can find plenty of people who make the mistake of equating BMI with obesity, that doesn’t change the fact that they are mistaken. Obesity is the unhealthy accumulation of fat tissue. Period.

  3. November 15, 2015 at 3:13 pm, Angela Meadows said:

    I must have missed that in the hundreds upon hundred of papers on obesity, national surveys and epidemiological data on obesity, and clinical guidelines on obesity. Oh, and all those HCP visits. Although if you’re suggesting that family doctors don’t understand this issue, I won’t disagree with you.

  4. November 16, 2015 at 5:18 am, Ted said:

    Thanks for your comment, Angela.

  5. November 20, 2015 at 7:07 am, Traci Malone said:

    It doesn’t matter whether or not obesity is not defined by BMI by anyone who understands the disease. What does matter is it IS being used to diagnose obesity by an overwhelming majority of health care providers, and being used by itself, not along with anything else such as body fat. And, it’s being used to diagnose millions of children based on growth curve percentiles. Ever since obesity was approved as it’s own independent diagnosis, the use of BMI alone for that diagnosis skyrocketed! Are we anywhere near creating a diagnosis that more accurately reflects the whole picture ( body fat %, body fat deposition location)? Seems like an incredibly difficult task to put together!

  6. November 20, 2015 at 7:48 am, Ted said:

    You have a good point, Traci. Thanks! It’s not impossibly hard, but it’s harder than just applying unconscious, visual bias.