What's the Problem With BMI And How Do We Solve It?
BMI is a ratio of weight and height. It was created by the statistician Quetelet in the 1830’s. The calculation is weight (in pounds,) divided by height (in inches) squared, multiplied by 703. (The final step is done to convert the formula from metric.) There are problems with this formula at every level.
First, Quetelet wasn’t trying to create a measurement for individual health. He was trying to create a definition of the “every man” which he described as “the type of perfection” that would then be used for comparison. In his work A Treatise on Man and the Development of his Faculties he wrote “everything differing from his proportion or condition, would constitute deformity or disease ... or monstrosity.”
This is obviously problematic on its face, but it’s made worse by the fact that almost his entire sample consisted of European cis white men. I urge you to read Sabrina Strings’ Fearing the Black Body – the Racial Origins of Fat Phobia and Da’Shaun Harrison’s Belly of the Beast: The Politics of Anti-Fatness as Anti-Blackness to understand, among many other things, the ways that the widespread use of BMI has institutionalized racism, white supremacy, and anti-Blackness within the medical system.
BMI has come to be used (with significant lobbying from the weight loss industry, but we’ll get to that) to pathologize bodies based on their size, despite the fact that two people with the same BMI can have vastly different health statuses, and two people with vastly different BMIs can have the exact same health status. It encourages a focus on body size manipulation, rather than health, for higher-weight patients. (Understanding, of course, that “health” is an amorphous, multi-factorial concept and is not an obligation, barometer of worthiness, or entirely within our control.)
There are issues with the basic math as well. Since height is squared rather than cubed in the formula, and our bodies exist in three dimensions, the number skews the farther someone gets from average height, either taller or shorter.
In one fairly rare, but especially ridiculous, example of the issues with this measurement, if someone loses height due to aging it can push them into a different BMI category - meaning that they would suddenly be considered part of an “epidemic” and at risk for health issues, and possibly denied surgeries and other healthcare procedures, simply because they are now a bit shorter than they were.
BMI has been malleable over time in response to the desires of the weight loss industry. In 1998, a committee recommended that the NIH lower the BMI categories, shaving 15-20 pounds off the definition of “healthy/normal weight.” Seven of the nine committee members had direct ties to the weight loss industry. The committee chairman was a former Executive Director and current board member of the Weight Watchers Foundation. Their recommendations gave the weight loss industry about 29 million new customers, literally overnight. CORRECTION: Katherine Flegal was not a member of this committee as I previously stated. I’ve notified the source where I found that misinformation.
BMI has a history (and present) of being used to deny healthcare to higher-weight people. Prior to the Affordable Care Act (and its provisions against insurance exceptions for “pre-existing conditions”), health insurance companies were allowed to consider BMI a “pre-existing condition” and deny fat* people health insurance. (Full disclosure – I was one of them for over ten years.) Currently, BMI limits are used to deny fat patients surgeries and other medical care they need for life and quality of life (often with a deeply hypocritical referral to weight loss surgery.) The negative impacts of all of this are subsequently blamed on fat bodies, and not the lack of appropriate care.
So BMI is built on problematic intentions, with questionable math, has been tinkered with by the weight loss industry, and has been utilized for widespread denials of healthcare to higher-weight patients, as well as encouraging doctors and other healthcare workers to practice stereotypes, rather than medicine, when working with these patients.
You may be asking if there is anything good about BMI? There is…
It’s completely unnecessary. We can just…let it go. And there is no need to replace it with other measurements of size or weight. Given that people of all sizes get the same health issues, we don’t need weight, size, or a ratio of weight and height, to be a middleman for health. We can simply take each patient individually and focus on supporting their health rather than manipulating their body size.
We could stop calculating BMIs for patients today and nothing bad (and plenty of good) would come of it. The diet industry could stop pouring money into studies that use questionable methods to correlate weight and health in order to sell their products. Instead, we could create research using people of diverse sizes (and diverse other identities as well) to test interventions across a spectrum of sizes, much like what was done for the COVD vaccines.
By centering the health of people of all sizes in healthcare (rather than focusing on wedging all patients into a narrow range of height/weight ratios,) patients are afforded better care and recommended interventions that provide higher efficacy with far less risk.
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*Note on language: I use “fat” as a neutral descriptor as used by the fat activist community, I use “ob*se” and “overw*ight” to acknowledge that these are terms that were created to medicalize and pathologize fat bodies, with roots in racism and specifically anti-Blackness. Please read Sabrina Strings Fearing the Black Body – the Racial Origins of Fat Phobia and Da’Shaun Harrison Belly of the Beast: The Politics of Anti-Fatness as Anti-Blackness for more on this.