AMA Takes a Swipe at Misuse of the Feeble BMI

BMI seems to be everyone’s favorite target for abuse these days. Depending on whom you listen to, it’s racist, sexist, useless, or useful.  Nobody really stands up for it, except as an simple, objective measure of weight for height. Now, the AMA decided to caution doctors about the misuse of BMI as a surrogate for fatness in clinical care. This decision came Tuesday at the American Medical Association annual House of Delegates meeting.

AMA Past President Jack Resneck explained the issue:

“There are numerous concerns with the way BMI has been used to measure body fat and diagnose obesity, yet some physicians find it to be a helpful measure in certain scenarios. It is important for physicians to understand the benefits and limitations of using BMI in clinical settings to determine the best care for their patients.”

The Overlay of Gender, Race, and Identity

On the opening day of the Boston Course in Obesity Medicine, Fatima Cody Stanford explained that one-size-fits-all thinking about BMI simply doesn’t work. Gender, race, and ethnicity are an important factor to take into account when interpreting. Thresholds of risk for health complications come at different values of BMI for each of these demographic factors.

Neglecting this basic fact gives rise to the misuse of BMI that AMA is warning about.

Facts, Beliefs, and “Vitriolic” Debates

For a really objective review of what we know about BMI, obesity, and mortality, we recommend a recent review by Luis Mestre and colleagues in Nutrition Today. As senior author, David Allison conceived and designed this paper, so it reflects very careful attention to the distinction between facts, beliefs, speculation, and unwarranted conclusions about BMI.

Fit but fat? A controversial topic that will remain so, because true believers are firm in their resolve that fitness matters more than fatness. Believers on the other side of this debate bring equal passion. Each side has its favorite observational (and thus not definitive) data.

A few things are clear. For example, the relationship between high BMI and mortality is changing over time. We don’t really know why, but the adverse relationship seems to be declining. It is also reasonably clear that overweight that falls short of obesity has an association with the lowest mortality. But again, the question of why this is so remains unanswered.

So we don’t expect the concerns about BMI to fade anytime soon. Nor do we expect people to abandon it altogether. Our only hope is for people to use it more carefully and sparingly.

Click here for the Mestre paper in Nutrition Today, here, here, and here for more on the AMA resolution about the misuse of BMI.

Bust of a Man in Profile with Measurements and Notes, sketch by Leonardo da Vinci / WikiArt

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June 15, 2023