Is the BMI BS?

Are we saying goodbye to BMI?

Body mass index (BMI) — the measure of body fat based on height and weight — has been around for decades. For years, your BMI has been used to determine whether you’re in a “healthy” weight range based on guidelines set by the World Health Organization.

Since it was created in 1972, BMI has been a standard measure of health and a screening tool for diseases including obesity. It’s also used to track population-level trends among public health.

But it turns out there are some serious issues with using BMI as an indicator of health — especially for women and people assigned female at birth.

​BMI limitations

Fatima Cody Stanford, M.D., M.P.H.,M.P.A., an associate professor of medicine at Harvard Medical School and an obesity medicine physician-scientist, said BMI has been flawed from the start considering it’s based on measurements of white men. “We are not men,” Stanford said. “I really see that as problematic for us to just assume that men are the baseline and standard because we do have differences.”

For example, women tend to have more body fat compared to men with the same BMI, but BMI doesn’t assess body fat percentage, which can have an impact on your health.

Stanford noted that women also experience changes in hormones throughout life that can affect body fat distribution. And she finds it frustrating that the differences between women and men aren’t being considered.

For women of color, the history of BMI becomes even more problematic. So much so that the American Medical Association (AMA) recently issued a policy change regarding BMI as a measure of medicine because of “its use for racist exclusion, and because BMI is based primarily on data collected from previous generations of non-Hispanic white populations.”

Under the new policy, the AMA recommends that healthcare providers take into account the different body shapes and composition across race/ethnic groups, sexes, genders and ages in addition to other risk factors. Considering about 6 out of 10 Black women are living with overweight or obesity in the U.S., and BMI is the sole indicator for diagnosis for the disease, this can have a major impact on the way providers approach diagnosis and health conditions — everything from treatment options to insurance costs.

Read: The Importance of Making Obesity Treatment Accessible >>

“I’ve been one of these people who are really trying to raise the alarm on BMI as a solo measure,” Stanford said. “BMI is not a health indicator — it just tells us height and weight. It doesn’t give me anything about the health of an individual.”

​The “M” doesn’t stand for muscle

Another major flaw is that BMI does not take into account body fat vs. muscle. And muscle weighs more than fat. For example, research shows Black people may have less body fat and more lean muscle mass than white people at the same BMI.

This can also pose an issue for people who are athletes and carrying more muscle, and muscle carries more weight, which makes the BMI an inaccurate measure of health.

Recently, you may have seen American rugby star Ilona Maher taking on the issue of BMI on social media. In a viral TikTok video, Maher responds to a commenter who criticized her weight, saying that Maher has a 30 BMI, which would put her in the obesity category by BMI standards.

Maher responded that she’s been labeled “overweight” her entire life despite being an athlete. “BMI doesn’t tell you what I can do. It doesn’t tell you what I can do on the field. How fit I am. It’s just a couple of numbers put together,” Maher said in the video. “It doesn’t tell you how much muscle I have, or anything like that.”

A few days later, Maher and the U.S. women’s rugby team won a historic bronze medal at the Olympics. So it seems the current and future plans changing the way we look at BMI couldn’t start soon enough.

​New guidelines for BMI

Currently, BMI is the only way to diagnose obesity. Stanford is one of the experts on a commission that is working on a clinical definition for obesity and updated guidelines for diagnosing and treating the disease.

Read: Is Obesity a Disease? Yes — and the Medical Community Is Finally Recognizing That >>

She said she’s dedicated her life and career to helping people who are living with obesity, and BMI just doesn’t work on an individual level. “People have been so married to this idea that this one number tells me about your health without delving beneath the surface,” Stanford said.“What is the cholesterol that goes with that number — what is the blood pressure that goes with that number?”

Stanford said the new recommendations from the commission, which should be out in September, put little emphasis on BMI and offer a more comprehensive look at the actual science behind obesity, which is key to treating the disease.

“Here we are in a place in 2024 where medicine does need to take an active stance and actually think about health and that’s what we’re doing,” Stanford said. “Obesity is a chronic disease and we should treat it as such.”