Your BMI isn’t a healthy metric — here’s why

Your BMI isn’t a healthy metric — here’s why

“In this world nothing can be said to be certain, except death and taxes,” Ben Franklin wrote in a letter to his friend Jean-Baptiste Le Roy in 1789. This tells us two things: first, that Franklin knew a quotable phrase when he saw one, and second, that he lived before the invention of the BMI.

In the past 50 years, body mass index (BMI) has gone from a relatively obscure demographic tool to an ever-present measure of personal worth. BMI above a certain number? Say goodbye to that life-changing surgery – in fact, good luck getting equal treatment in almost any medical setting. Prepare to be undervalued and underpaid at work – if you can even get a job in the first place – and if you are still in school, expect to be evaluated more harshly and to be viewed by your teachers as “more of a burden” than your peers The least weight. Frankly, it’s not surprising that a high BMI is associated with lower self-esteem, higher rates of depression and anxiety, and a greater likelihood of facing abuse from family and romantic partners.

And the real kicker in all this? High body mass index.

BMI wasn’t tailored to you

With the level of importance we tend to attach to the scale, you might expect BMI to be the result of years of research by health experts. it’s not. In fact, it was never intended for use on individuals at all.

“Body mass index was introduced in the early 19th centuryy “The 20th century was led by a Belgian named Lambert-Adolphe Jacques Quetelet,” Stanford University mathematician and well-known science communicator Keith Devlin explained to NPR in 2009.

“He was a mathematician, not a doctor,” Devlin noted. “He produced the formula to give a quick and easy way to measure the degree of obesity in the general population to help the government allocate resources. In other words, it is a 200-year-old breakthrough.”

To a mathematician or statistician, this kind of metric makes sense: after all, over a large enough sample size, the average actually tends toward the truth. But it was never intended to be a measure of health, or even obesity, but was originally just an observation meant to rank some theoretical “common man.”

And Yesit was almost exclusively men on whom Quetelet based his numbers—specifically, European Men, mostly from France and Scotland, and if you’re starting to see a problem here, boy, hold on to your hats, because we’re not done yet. The concept does not assume that you are a 19-year-old white maley Century sang. It also assumes a mostly sedentary lifestyle, a working age and able body, an average income and educational level – hell, even an average complexion. (Three guesses as to what Which He was).

This is despite the fact that “our bodies, by nature, have some distinct characteristics that are driven by our sex, including that females generally have less muscle mass and greater fat mass than males,” noted Nick Fuller, leader of the Charles Perkins Center Research Program at the University of California. . University of Sydney, in a 2022 article for The Conversation. “We also know that muscle mass decreases and changes throughout the body as we age.”

Likewise, “research has also confirmed significant differences in body weight, composition, and disease risk based on race.” For example, he wrote: “People of Asian race should have a lower BMI, and people of Polynesian race could be healthier when their BMI is higher.”

Even in more modern forms of the index, the underlying data has been overwhelmingly white and male. In other words: BMI is not a population measure and not only is it not an individual measure, but you may not even be a member of the population it measures.

BMI does not measure health

So how can a relatively obscure population-level statistical data point become a ubiquitous surrogate for individual health? Well, it becomes clearer when you learn who the two main supporters of the use of the measure in health care are: insurance companies and pharmaceutical companies.

“By 1867, the first American life insurance company created height and weight tables for the purpose of charging obese customers more,” author and journalist Aubrey Gordon explained in a 2021 episode of the Phase Maintenance podcast. “The whole history of this is a guy who thought he was doing population analysis, and then a series of people who latched on to it largely for profit motives — first insurance companies and then pharmaceutical companies.”

Calculating someone’s BMI is cheap and easy, and boils down a whole bunch of questions to a single relationship between two measurements – and it’s no wonder it works. Looking at it from this perspective, its shortcomings as a measure of health become even more apparent.

For proof, look no further than your favorite athletes. “(BMI) does not take into account the relative proportions of bone, muscle and fat in the body,” Devlin noted. “But bone is denser than muscle and twice as dense as fat, so someone with strong bones, good muscle, and little fat will have a high BMI.”

That’s why using BMI alone will give you counterintuitive results like Tom Brady (BMI: 27.4; overweight and obese using pre-1998 definitions), or Jonah Lomu (BMI: 34.5 at his peak; morbidly obese ), or Shaquille O’Neal (BMI): an amazing 40.3 in his prime; is obese) – or why Chris Hemsworth (BMI: 29.0) was playing a near-obese character in Thor: Love and Thunder Even (and perhaps especially) after A montage of polishing the character of the same name.

“Because of the way Quetelet found it, if a person is overweight or obese, they will have a high BMI,” Devlin explained. But “it does not go the other way around. A high BMI does not mean that an individual is overweight, let alone obese.”

When BMI is compared to other methods of measuring health, its weaknesses really become apparent. Take, for example, a 2016 study of more than 40,000 Americans that concluded that “nearly half of individuals are overweight, 29% of individuals are obese, and even 16% of people are obese.” Obese type 2/3 were metabolically healthy” while “more than 30% of normal” overweight people were cardio-metabolic unhealthy.

Likewise, the indicator cannot take into account body fat distribution – this matters a lot more than you might think. “If you have fat stored around your stomach, your risk of chronic disease is much higher than people who have fat stored around your hips, because that’s an indicator of the amount of visceral fat you have — the type of fat,” Fuller explained. Inside the abdomen, which increases the risk of stroke, type 2 diabetes, and heart disease.

“(BMI) lacks accuracy and clarity, and in its current form, it misses the measurement of many important factors that influence disease risk,” he wrote. “This should never be the only measurement you use.”

BMI is statistical nonsense

But you may wonder why BMI is so useless? Well why won’t He is?

The legitimacy of BMI as a meaningful measure is on shaky ground from the start: Ultimately, “there is no physiological reason to normalize a person’s height,” Devlin noted. This is something Quetelet decided to do for somewhat aesthetic reasons – he wanted the collected data to follow a Gaussian curve, and this was the ratio that provided that. (“If you can’t fix the data, fudge the formula!” says Devlin.)

After calculating your BMI, things get more complicated. According to the CDC, a BMI of 25 or more makes a person “overweight.” 30 or more and the classification is “obese”. But no one really knows where those cutoffs come from: “These are arbitrary numbers,” Katherine Flegal, a consulting professor of obesity epidemiology at Stanford University, told The Washington Post.

As such, it’s largely useless for measuring health — and, frankly, it’s strange that we’re still using it.

S wrote Bryn Austin, professor of social and behavioral sciences at Harvard T.H. Chan School of Public Health, and Tracey K. Richmond: “Imagine a salesperson coming into your clinic’s office to demonstrate a new tool for measuring your patients’ health.” , assistant professor of pediatrics at Harvard Medical School, wrote in a 2022 MedPageToday article about the drawbacks of the BMI as a diagnostic tool.

“They tell you this is not as good as the measures already taken. It even works worse in the elderly and athletes. This will turn away large numbers of patients, while worsening symptoms in others. Then the salesperson adds sheepishly, ‘At least it’s cheap and easy to use .

“Are you going to buy it? Of course not. Who in their right mind would do that?”

The content of this article is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of qualified health providers with questions you may have regarding medical conditions.

All “explainer” articles are verified by fact-checkers at the time of publication. Text, images and links can be edited, removed or added at a later time to keep the information up to date.

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