Muna-Udbi Ali, an Assistant Professor in the Faculty of Environmental and Urban Change at York University, has experienced the dangers and unreliability of Body Mass Index (BMI) as a diagnostic screening tool first-hand.
“Too often, Black women’s real health concerns are ignored as doctors tell them they just need to lose weight,” says Ali. “This can lead to dangerous outcomes.”
Yet, BMI is still widely used.
From health apps to clinical intake forms, clinicians categorize patients from “underweight” to “obese” by calculating a person’s weight and height to generate a BMI classification. The assumption: a high BMI raises the risk of health problems.
But researchers, clinicians and advocates have been raising concerns about the BMI, saying it’s not reliable, is not a comprehensive indicator of health and using it can have disastrous results, especially for racialized populations.
“Why would we be using a tool that has historically been designed on purpose to exclude people?” asks Aly Bailey, assistant professor in Recreation and Leisure Studies at the University of Waterloo, who has co-authored an article in the peer-reviewed journal Body Image advocating for the refusal of BMI.
Ali experienced what could have been disastrous results first-hand in the summer of 2020 while living and teaching in San Diego. For several days, Ali experienced excruciating headaches that impacted her sight. Her neurologist and ophthalmologist persuaded her to go to the emergency department, where hospital staff took note of her weight, calculating her BMI, which indicated she was obese.
Rather than attend to her pain, she was told she needed to lose weight. No additional tests (such as blood sugar or cholesterol) were conducted. In fact, she was not even sent for an MRI until her neurologist called the hospital to demand it.
The scan revealed a blood clot in the brain, drastically changing her care. She was the first person in southern California to experience a blood clot in the brain because of COVID.
“It was so infuriating. When I was just seen as a Black, fat body, I was blamed for my pain and pathologized,” Ali said. “When I was seen as a dying body, in a potential project (the first blood clot in the brain caused by COVID), I was given care … and so now they stopped focusing on the BMI.”
BMI has a troubling history, one that is intertwined with racism. A 2025 article in the International Journal of Behavioral Nutrition and Physical Activity outlined its history while asking “BMI or not to BMI?” The precursor to BMI, the Quetelet Index (developed by Adolphe Quetelet in the 1840s), was used by Francis Galton in the 1880s to compare characteristics of different races. Galton was Charles Darwin’s half-cousin and coined the term eugenics. Nutritionist Ancel Keys took the Quetelet Index to its current form of the BMI in the 1970s. Quetelet, Galton and Keys all used the index to understand differences at the population level.
BMI has a troubling history, one that is intertwined with racism.
It wasn’t until the 1990s that BMI began to be used on the individual level, coinciding with the advent of medications to support weight loss, according to Katherine M. Flegal in the American Medical Association Journal of Ethics.
Ramanpreet Annie Bahra, co-founder of the Canadian Sociological Association’s Fat Studies Research Cluster, says that over the course of time BMI has become normalized in clinical settings. “We’ve naturalized it into medical vernacular.”
While BMI is ubiquitous in health care, so are its challenges. Roberta Heale, a nurse practitioner who leads a virtual menopause clinic serving patients in Ontario and Alberta, says that the problems with BMI are an issue in menopause care. “As estrogen lowers, there’s a transition or movement of fat from hips to waist, and that’s visceral fat, which is more dangerous for chronic disease risk,” yet many menopausal patients have no change in their weight. “Their BMI has not changed yet their risk for cardiac issues, diabetes, has changed.”
Endocrinologist Gillian Booth, a scientist at MAP Centre for Urban Health Solutions in Toronto, says that there’s a lot of evidence about the unreliability of BMI among racialized groups.
“Different ethnic groups carry weight differently,” she says, citing South Asian and Southeast Asian populations. “The risk of diabetes will happen at a lower BMI.”
Diabetes Canada notes that BMI is less accurate for athletes, people with larger bodies who have little visceral fat and people with disabilities. In its most recent policy proposal, Gender Affirming Care Nova Scotia says that weight-based models perpetuate barriers for trans people who need life-saving care.
“BMI is also used for gender affirmation surgery,” says Bahra, who is completing her PhD at York University.
BMI is used widely in national and global reports about chronic disease risks, including by the Public Health Agency of Canada (PHAC). Justin Lang, a research scientist with PHAC’s Centre for Surveillance and Applied Research in the Health Promotion and Chronic Disease Prevention Branch, says “I completely agree there are limitations, especially when at the individual level and in the clinical setting.”
PHAC’s chronic disease surveillance research uses BMI at the population level using self-reported data from Statistics Canada. This data is looked at in relation to other measures such as physical activity, sleep and environment, says Lang. “We don’t advocate making full decisions on BMI alone. We look at it as a single measure that’s part of a larger toolkit.”
Lang says there may be measures other than BMI that are more precise yet would be much more difficult to gather at the population level. “The most feasible way to collect data is through self-report, we can collect data on a large number of the population.”
At the individual level, alternative approaches to BMI have been proposed for several years, along with the recognition that a singular measure can’t tell a health-care provider about someone’s health. “Determining whether an individual is healthy is best left to a qualified nurse practitioner, not a number,” says Michelle Acorn, CEO of the Nurse Practitioners’ Association of Ontario (NPAO), in a written statement.
Body Roundness Index and waist circumference are potential alternatives that are relatively easy to implement and provide more information than BMI. Bone densitometry, also called dual-energy X-ray absorptiometry (DEXA or DXA) is more precise, measuring body fat, muscle and bone density but is significantly more resource-intensive as it cannot be self-reported.
Beyond alternative measures, discussions about BMI have led to critically looking at how our society values different bodies. Ali’s personal experience and her own work looking at the experiences of Black communities suggest it is impossible to talk about bodies without talking about race: “Too often, Black women’s real health concerns are ignored as doctors tell them they just need to lose weight.”
Says Bailey, who encourages moving away from using BMI altogether: “Let’s move forward with some more ethical ways of thinking about bodies and sizes and giving folks agency in their ability to self-describe.”
For Bahra, this agency would include patients making choices. “You know you don’t have to get weighed when you go to the doctor. You could say no, and what would happen then?”
