As new Statistics Canada data reveals that two-thirds of Canadians are considered overweight or obese, researchers are urging the public and policymakers to rethink how we define and measure health - starting with one of the most used metrics - the body mass index (BMI).
For decades, BMI - a simple ratio of weight to height - has been treated as a gold standard in public health and medical practice. It influences everything from fitness apps to clinical decisions about surgery eligibility and pain management. But according to a new Waterloo-led study, BMI tells only a fraction of the story about a person's health and does more harm than good when used.
"It is becoming more well-known that BMI doesn't measure what many people think it does," said Dr. Aly Bailey, the lead author of the study and a professor in the Department of Recreation and Leisure Studies at Waterloo. "It cannot distinguish between muscle and fat, doesn't account for where fat is distributed in the body and overlooks important factors such as age, sex and race. Two people can share the same BMI but have completely different health profiles."
The researchers warn that BMI's limitations have real-world consequences. It can influence access to medical care, reinforce harmful stereotypes about "normal" bodies, and contribute to stigma - particularly for people in racialized, disabled, older, or larger bodies.
Originally developed in the 19th century to statistically identify the "average man," the BMI is a measure based on height and weight. "However, what many people often don't know is that the BMI was never created with health in mind at all," Bailey said. "Instead, it was a statistical tool used to justify racist and anti-fat ideas and other forms of discrimination. It quickly became a so-called measure of health, beauty, and fitness."
Building on calls made by activists, the study outlines possible paths forward. One approach is to continue using BMI, but only with explicit recognition of its racist and problematic history. Another is to consider more nuanced and valid measures of body size, or include indicators that track actual health outcomes. The other, bolder option, which the authors advocate the most strongly, is to reject BMI altogether.
The study, The body mass index: What's the use?, was recently published in Body Image.
