BMI is not an accurate measurement of one's health. Why are we still using it?

Scales and BMI measurements are a flawed way of looking at our health. The case for ditching them

By Mary Elizabeth Williams

Senior Writer

Published December 4, 2022 7:30PM (EST)

A Measuring Tape on a Scale (Getty Images/artisteer)
A Measuring Tape on a Scale (Getty Images/artisteer)

I arrived at my doctor's appointment on the Monday morning after an indulgent Thanksgiving weekend and did exactly what you'd expect. I went to the restroom to urinate. I took off my shoes and my cardigan; I took my keys and phone out of my pockets. Only then did I step on the scale. I know, intellectually, that my weight tells only a very small part of the story of my health. I know that my BMI — a measurement arrived at by dividing one's weight by the square of one's height — is a wildly unreliable tool. It doesn't reveal my fitness, my muscle mass, my strength, or my cholesterol levels.

There's a pretty good chance you, too, have tried to remove a few ounces before a doctor's office weigh-in. The scale always seems to be a test, one in which the smaller the number, the better the score. Why are we still putting ourselves through this? And what if I told my doctor I didn't want to do it any more?

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The body mass index can be fine as a shorthand assessment, a calculation involving a person's weight and the square of height. First developed nearly two hundred years ago by Belgian statistician Adolphe Quetelet, it was intended a tool for determining weight trends based on larger population samples. It was not supposed to be a medical tool for individuals, and it was devised — stop me if you've heard this one before — pretty much with white European males in mind. It's safe to assume Quetelet probably wasn't thinking when he came up with his, "Hey, will this thing serve people of different races, ages and genders, for generations to come?"

As a recent Guardian feature by Donna Lu notes, it doesn't. "The metric overestimates obesity in African-Americans," she says, while "for Asians, the health risks linked to obesity occur at a lower BMI." So the fact that at this stage in history, the CDC's adult BMI calculator offers a "healthy" weight range without any variables for ethnicity, gender or weight distribution, is absurd. 

The mainstreaming of BMI took off in the 1970's, when American physiologist Ancel Keys began promoting it as a reasonably reliable and easy means of estimating body fat, and by extension, potential health risks. But Keys was a researcher. Like Quetelet, he was looking at groups and trends, not your personal medical chart. Earlier this year, the Obesity Medicine Association declared that "There are several disadvantages to using the calculation to determine obesity.... Much work remains to be done to produce more accurate BMI guidelines that can be applied to more people globally as well as nationally in the United States."

So if you — or your health practitioner — are operating on the idea that the number of pounds you're carrying or your BMI number are an automatic indicator of any underlying conditions or just your value as a human being, they are not. And instead of being useful, if poorly interpreted, those numbers can set you up for problems.

At the International Congress on Obesity in Melbourne this fall, attendees explored how "Judgements based solely on weight metrics like BMI, and unrealistic weight goals, can unintentionally lead to poorer health outcomes," noting that "Declaring 'a normal weight range' can fuel weight bias and stigma, demotivate patients and promote eating disorders." It can also discourage patients from getting a true picture of their health.

"I have had clients who don't go for their regular checkup because they're embarrassed about their weight."

"The tougher parts come in when the doctor doesn't know how to talk to you about your weight, or you don't know how to talk to the doctor about emotional reasons for eating," says Bonnie Taub-Dix, RDN, creator of BetterThanDieting.com and author of "Read It Before You Eat It - Taking You from Label to Table." "I have had clients who don't go for their regular checkup because they're embarrassed about their weight, and they want to wait until they lose weight to go to the doctor."

I understand that apprehension. I don't own a scale and I avert my eyes at the doctor's office, but I've still had nurses loudly and excitedly blurt how much my weight has changed since the last time. And I suspect that for many of us, that doctor's scale represents the intersection of perceived self-image and actual physical health. 

Rather than thinking of the scale as being a primary resource for how we are assessed and how we assess ourselves, we need to look at the big picture — and pull in other metrics. "I don't want this to sound trite," says Taub-Dix, "but I think clothing is better than BMI. If you wore something last winter and now it's tight, there's a message there." Taub-Dix clarifies that she is not talking about "trying to squeeze into your wedding gown or jeans your wore in high school," but just a "realistic" year-to-year change; our bodies innately change as we get older. "Clothing that fit you when you looked and felt your best is a great guide to give you a message about your body," she continues. It's also helpful to consider where clothes fit as well as how — if your pants legs and sleeves are getting tight, it might be from working out more. If it's the waistband, that can be a warning sign. 

"Waist circumference is a more insightful measure of an individual's health than BMI because it tells us about the amount of fat surrounding essential organs," says Dr. Anita Lwanga, an internist in Watertown, New York. "The more fat one has surrounding their vital organs, the higher their risk of developing diabetes, heart disease, fatty liver disease, hypertension, and mortality. BMI doesn't differentiate between weight due to fat or muscle. Waist circumference is adjusted for an individual's gender, whereas BMI is not." 

There are other indicators to pay attention to as well. "I think the body mass index is a good baseline indicator for obesity in general," says Sarah Lutz, a nurse practitioner at University of Michigan Health-West. "We do know that diabetes, high blood pressure, high cholesterol are related to obesity." (It's also linked to a high risk for certain kinds of cancer.) But she adds, "There is some genetic component to high cholesterol, high blood pressure. Those things aren't modifiable, but weight typically is."

"Not every medical visit requires a weight."

It's estimated that nearly 30 million Americans will have an eating disorder in their lifetime. Plenty more struggle with the stress, anxiety and baggage of body image and the quantification that the scale brings. Dr. Katherine Hill, a pediatrician and eating disorders doctor and VP of Medical Affairs at Equip, offers some advice. "If being weighed is triggering or makes a patient uncomfortable, they should feel empowered to speak up and share this with their medical provider," she says. "While there are some medical conditions that do require a weight to be taken, not every medical visit requires a weight. If a weight is needed information for the medical provider, patients can request to be weighed backwards to avoid seeing their weight number and request that the number is kept hidden. Many doctors and medical providers are supportive of these requests, especially if they help patients feel more comfortable and less triggered." And Bonnie Taub-Dix says, "I think that you need to know yourself. If you're going to weigh yourself on a scale you need to know what it really means. It's one measure that is giving you information about your body weight, but it's only one measure."

Numbers by themselves don't mean much without deeper context and compassionate follow-up. Sarah Lutz says, "I think blood pressure and cholesterol levels are additional good indicators for overall health — and then having a conversation with patients. Are you exercising? What does your diet look like? What is your alcohol use? Those are all things that I like to have conversations with my patients about." She says, "I saw 17 patients today, and I don't know what one of them weighed. I don't care about that number. I care more that we're keeping them healthy."

That's a sane approach to what can be a deeply sensitive issue. And when I head with unease toward the scale in my doctor's office, I try to remember a visit when I was in treatment for cancer, and a fellow patient getting his vitals taken near me. "You've gained five pounds," I heard the nurse tell him from the other side of a curtain. "Yeah," he replied. "Life is good."

By Mary Elizabeth Williams

Mary Elizabeth Williams is a senior writer for Salon and author of "A Series of Catastrophes & Miracles."

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