The BMI Is Junk Science

I showed up to my last doctor’s appointment with trepidation. I’m 46 years old and generally healthy. I don’t have diabetes or high-blood pressure; my cholesterol is fine, and I’m active. But I am overweight—obese, actually, according to the Body Mass Index (BMI), a mathematical formula that divides a person’s weight in kilograms by their height in square meters.

Doctors have been relying on the BMI to judge individual health for more than a century. At my recent appointment, which was with a doctor I’d never seen before, my BMI was front and center in our consultation. My physician told me I was obese, and then zeroed in on my risk of becoming pre-diabetic. Doctors have been telling me I’m essentially pre-pre-diabetic for the past 15 years, but I have yet to experience any complications from this nebulous diagnosis. Next the doctor noted that my cholesterol has increased slightly, neglecting to mention—perhaps neglecting to even think—that this likely has more to do with my age and family history than my current weight.

She didn’t ask me about my activity levels. I walk over 10,000 steps a day, I work out at OrangeTheory twice a week, and I ski at least 20 days each winter. Thanks to my BMI, she wasn’t interested in that information. I left the office feeling ashamed and disheartened, like so many times before: this one number had eclipsed everything else about me that a healthcare provider should be looking at.

The BMI was never intended to be an individual health indicator or an excuse for physicians to weight-shame their patients. It has become a pervasive, blunt tool that not only promotes fatphobia but contributes to worse health outcomes for many of us.

This conversation isn’t new. There’s been significant pushback against the BMI for over a decade, with experts telling national media outlets that it’s “fairly useless,” “a disservice,” and “physiologically wrong”—but the message still has not sunk in. We talked to more experts in order to write this reminder: your BMI does not matter.

The BMI was created by a Belgian astronomer and mathematician named Adolphe Jaques Quetelet in 1835. Quetelet wasn’t a doctor. In fact, he was most well known for his sociological research that focused on identifying the qualities of l’homme moyen—the average man—who he saw as the ideal. Even Quetelet never intended his formula to be used on individuals. Instead, he used it as a means of calculating the collective weight of a population to assist in the allocation of resources.

The population Quetelet measured and based BMI on was limited to caucasian men—which means that doctors today are still going along with a formula that uses white male bodies as the gold standard of health and longevity. As America slowly realizes that these bodies are not the only ones that matter, it’s time for our health care system to catch up, too.

“To determine someone’s health and their risk factors based on their height and weight sounds really silly when you say it that way,” says Ashley Robbins, a primary care physician at the Guadiani Clinic, an outpatient eating disorder facility in Denver. “[The BMI] doesn’t take into effect someone’s muscle mass, someone’s bone density, someone’s bone framing. We all have different size body frames. It doesn’t take into account someone’s race or ethnicity or socioeconomic status—there are so many factors that are missing.”

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Athletes can easily fall on the wrong side of BMI. Although the old adage that “a pound of muscle weighs more than a pound of fat” isn’t exactly true—a pound is a pound—muscle is much more dense than fatty tissue, meaning that a pound of muscle takes up less physical space in the body than the same amount of fat. So, muscular people can tip into the overweight or obese range even with low percentages of body fat.

Wendy Deacon, a former healthcare executive with a masters in exercise physiology recalled measuring BMI and body fat measurements as part of her internship at University of South Carolina in the early nineties. “We were regularly contacted by men who wanted to go into the military,” she said. “But, as athletes, many of them had a BMI value that was too high and their application was subsequently denied. They contracted the University to conduct a body fat test as part of their appeal, and, most of the time, the body fat percentage test was sufficient to be accepted into the military.”

But you don’t have to be ripped or have a low body fat percentage to be a healthy and capable athlete. I’ve been varying levels of “curvy” all my life, and still competed in sports. I played four years of varsity tennis at a state-ranking high school and for one year of college. I’m an expert skier who can handle any inbound terrain at a resort. And, recently, I’ve taken up heavy lifting at an independent, women-owned, incredibly inclusive gym called PeaksFit in Boulder, which has given me even more confidence.

And I’m not alone. Plenty of professional athletes—look at the entire roster of the Denver Broncos, for example—have bodies that would be considered overweight according to their BMI. Mirna Valerio, who also goes by The Mirnavator and has partnerships with major athletic brands including L.L. Bean and HydroFlask, is a marathoner, ultrarunner, and trail runner with a BMI of approximately 39.2, nine points above the line that establishes obesity according to the National Institutes of Health. Plus-size runner Mindy Smith has completed multiple 100-mile races and is even signed up for her first 200-miler next year. “I feel strong when I’m running,” she says. “My mental health is more important to me than my BMI. There’s just so much more to health than that number.”

There isn’t robust scientific evidence associating BMI alone with bad health outcomes. “A lot of the data that ties obesity to metabolic issues and heart disease are all correlations, and correlations in research are simply not as strong as causation,” says Robbins. “It’s just incredibly problematic. I think most physicians come to medicine from a good place and don’t have any intentions to harm patients. But, the way that our system is set up and the way that we’re trained to use [BMI] to make assumptions about someone’s health already sets the visit up for failure. Because that number has nothing to do with the human you are about to see.”

Doctors often prescribe weight loss to people in larger bodies first to treat any and every medical issue, often to the detriment of their patients, who might be suffering from a condition completely unrelated to their weight or due to other mitigating factors such as stress levels, genetics, socioeconomic status, and even mental health.

“If your BMI is over a certain cutoff, we’ll say, ‘You need to bring it down,’ without asking any other questions,” says Dr. Leslie Williams, a primary care physician at The Mayo Clinic in Phoenix, Arizona. “And, on the flip side, if your BMI is below a certain number, you [may] be congratulated without us asking any other questions. It’s not helpful.”

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Physicians’ attitudes toward weight can also deter patients from seeking care in the first place. “I can’t tell you how many of my patients in larger bodies are like, ‘I got tired of going to the doctor for things like a sinus infection or an ear infection, and they start commenting on my weight,’” says Robbins. “I have a lot of patients who have missed out on routine screenings or who could have been seen earlier for a medical issue that has worsened, because they were avoiding care due to the shame and stigma they experience.”

Robbins believes that the most prescribed treatment for obesity—dieting—can actually cause more damage. “We know that dieting doesn’t work,” she says. “In fact, it can actually lead to even more weight gain than if the person hadn’t gone into food restriction.”

There’s also the pervasive daily psychological harm that fat people experience from fatphobia. The constant feeling of bodily shame can lead to depression, eating disorders, even self-harm and suicide.

Ragen Chastain, a certified health coach, functional fitness specialist, author, and speaker (who incidentally also holds the Guinness Book of World Records title for the heaviest person to ever complete a marathon) has spent the last decade talking to medical professionals about weight-neutral healthcare and how the BMI can cause harm. “I got into endurance sports, and, at events, there was actually a lot of support. I didn’t face so much weight stigma, but the structural weight stigma I faced in endurance sports was much higher,” she says. “When I moved from marathon to triathlon, [I discovered that] they literally don’t make a bike that works for my geometry. There’s not a single wetsuit in the world that fits me. So, getting kitted out was in some ways harder than the training.”

“When I first started training as a fitness instructor, I was deeply enmeshed with diet culture and did a lot of harm,” she said. “It’s hard to be honest about that—to say that I was misinformed and hurt a lot of people, while in a position of authority. ”

Robbins has this advice for doctors who treat larger patients moving forward: stop weighing people. “There are only a handful of reasons why you need to weigh someone during an office visit,” she said. “Knowing [your patient’s] weight should not affect or change your treatment plan. You can get so much more information from your patient and provide so much more support when they know they are not being judged and lectured on their weight.”

Instead, she recommends that doctors rely on blood panels and other metrics such as blood pressure and resting heart rate that can often tell a more accurate story about someone’s health.

Regan Chastain travels around the country speaking about this issue to health care providers. But, there are numerous ways you can advocate for yourself as a patient. If you are in a larger body, search for a weight-neutral doctor who believes you deserve the same care regardless of your size. She recommends starting with this list of providers that was started by singer Mary Lambert. “You can always call ahead and say ‘I need somebody that practices weight-neutral health care—that means caring for me without diets or prescribed weight loss,” she said. Or if you’re already in a doctor’s office and a provider starts prescribing weight loss for a physical problem, Chastain recommends that you ask: “What would you do for a thin person with these same symptoms?” In short, don’t be afraid to push back and stand up for the care you deserve.