OW2023: Have We Tortured BMI Enough?

We’re starting to feel pity for the poor, tortured metric of BMI. Put BMI into your Google search box and the top suggestion is “BMI inaccurate.” The top news about BMI right now comes from Nature and it explains “Why BMI is flawed – and how to redefine obesity.” And therein lies the problem. BMI is a useful metric that gets misused to define a clinical condition of obesity.

At ObesityWeek 2023, Diana Thomas explained it succinctly in a presentation of the pros, cons, and implications of using BMI. She told us that the real problem is the use of fixed BMI benchmarks to define obesity:

“Yes, the problem is not BMI. Using one-size-fits-all thresholds to define obesity is the problem. We are at a place now where we don’t need thresholds. Thresholds were there to make things easy but we can now program in deep neural networks straight into devices or even physicians phones to predict personalized risk to various diseases.

“We need to let go of the 1950s way of doing things.”

Do Other Measures Measure Up?

One of most recurrent gripes about BMI is that it is not a direct measure of health. In fact, this is a good point to remember. However, John Jakicic presented data at ObesityWeek to point out that it’s not such a bad correlate for a health risk such as blood pressure.

He examined the relationship between BMI and American Heart Association categories of blood pressure. He compared that to alternative indicators of adiposity – body composition with dual-energy x-ray absorptiometry (DXA), and waist circumference. Notably, he found that all of them correlated with blood pressure, but:

“Stepwise regression showed that BMI, but not percent body fat or waist circumference, was associated with elevated BP (p<0.001).”

Maybe we should let up on the poor, tortured measure of BMI. Instead, all that energy might be better devoted to examining how we use it and a how to fully assess the health of a person who might have obesity.

Click here for the presentation slides by Thomas and here for Jakicic’s research abstract.

St Anthony the Hermit Tortured by the Devils, painting by Sassetta / WikiArt

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October 18, 2023