For decades, the body mass index (BMI) has shaped how doctors, policymakers and even fitness apps define health. But a new University of Waterloo study warns that it’s time to move on.
“It is becoming more well-known that BMI doesn’t measure what many people think it does,” said Dr. Aly Bailey, lead author of the study and professor in Waterloo’s Department of Recreation and Leisure Studies. “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 study, published in Body Image, arrives as Statistics Canada reports that two in three Canadians are now considered overweight or obese. Yet BMI, a 200-year-old formula dividing weight by height, fails to tell the full story of who is actually healthy and who may be at risk.
Originally developed in the 19th century as a way to describe the “average man,” the BMI was never intended to diagnose or assess health.
“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.”
Those biases, the researchers say, still influence how BMI is used today, from determining surgery eligibility to shaping public health campaigns. The result can be harmful stereotypes, weight stigma and barriers to care for people in larger, older, racialized or disabled bodies.
The authors outline three possible paths forward: continue using BMI but acknowledge its history and limitations; replace it with more direct indicators of health, such as blood pressure or body composition; or reject BMI altogether. Bailey and her team favor the last option, arguing that real measures of health should be individualized and holistic.
The authors reported no external funding for this research.