Since the 1970s, health professionals have used the body mass index as a measure of obesity and health. It’s listed on medical records and used to assess for various diseases, including diabetes. And it’s easy to calculate. Any number of online tools can spit out a person’s BMI, determined by dividing their weight (in kilograms) by the square of their height (in metres) to estimate their amount of body fat.
However, detractors have long denounced BMI as a poor metric. It’s been criticized for conflating weight with health, not taking muscle mass and bone density into consideration and not accounting for sex or racial differences, since the original data that BMI was built on is based on measurements of white men.
Earlier this year, for example, American rugby player and Olympic bronze medalist Ilona Maher went viral for speaking candidly about BMI, and how her BMI of 29.3 categorizes her as “overweight” despite her obvious health and fitness.
In 2023, the American Medical Association acknowledged that BMI is an “imperfect way to measure body fat.” And an English study from 2021, with a more diverse data set, found that current BMI measurement standards for assessing diabetes risk need to be adjusted for different ethnicities, as the one-size-fits-all approach doesn’t work for everyone.
Recently, an alternative has been gaining traction. First introduced in 2013, the body roundness index uses waist circumference and height to calculate an approximate amount of visceral fat, which is found deep within the abdomen surrounding organs such as the stomach and liver. Excess visceral fat has been found to put a person at risk for obesity, kidney disease, diabetes and cancer.
It’s for this reason that some people believe BRI is a better guiding metric for measuring health. But others see it as more of the same story: one number that cannot fully capture an individual’s health and might do more harm than good.
The Globe asked four experts to share their thoughts on BRI.
What an obesity expert thinks
Sanjeev Sockalingam, a Toronto physician, scientific director of Obesity Canada and a professor of psychiatry at the University of Toronto, says BMI is deeply flawed and doesn’t accurately reflect diverse body types. “There are ethical, cultural and some might say racist underpinnings for BMI as the sole index of obesity measurement,” he said.
But while using waist circumference may be “one step better” than just height and weight, BRI still does not capture the complexity of a person’s overall health, he says. And it could further contribute to a negative view of bigger bodies by attributing “good” and “bad” numerical values based on roundness.
Sockalingam instead refers to the Canadian obesity guidelines, which define obesity as a chronic health condition that negatively affects mental and physical health and can lead to comorbidities such as diabetes and high blood pressure.
BRI can’t measure the amount of fat an individual has, nor can it measure a person’s mental or physical well-being, he explains. “Someone with a higher BRI may not have diabetes, high blood pressure or functional impairment, but another person with a similar BRI might have those things. Those are not the same in terms of thinking about or defining obesity.”
What a mental health expert thinks
According to Danielle MacDonald, a psychologist in Toronto who works for the University Health Network’s eating disorder program, BMI has long been identified as “problematic and limited.” BRI, or any new number won’t fare any better, she says. “The average person may not always understand the nuances of what those numbers mean or how they might be used, and it could potentially lead people down a path of internalizing negative messages.”
MacDonald emphasizes that using a single number to classify a person’s health could have a negative impact on their mental health. A high BRI might result in someone feeling pressure to lose weight and engage in unhealthy behaviours such as restrictive dieting or excessive exercising. “Often, when people start engaging in extreme behaviours like that, it has a downstream effect leading to things like low mood, anxiety, low self-esteem,” she said.
People in larger bodies continue to face a lot of stigma in society, she adds – and that’s something BRI can’t fix.
What a dietitian thinks
“For starters, I really dislike the name,” said Rachel Murphy, an associate professor at the University of British Columbia’s School of Population and Public Health. “The name does imply that ‘round’ is not a positive thing.” As a result, she says, there’s the potential for body shaming. “But I think the concept is good. We know fat distribution around the midsection, the abdomen specifically, tends to be more metabolically active and strongly linked to metabolic health and disease.”
However, Murphy adds, the implementation of BRI into clinical settings could be as problematic as its name. Clinicians would need to be trained to measure accurately and sensitively, recognizing that BRI doesn’t account for the variation in body composition (and related health effects) in people from different ethnic backgrounds.
More population-level research with broader and diverse data sets is needed to understand whether BRI really is better than BMI, Murphy says. For now, she considers neither to be fair or conclusive.
What a fitness expert thinks
Sara Gilbert, a clinical exercise physiologist and president of the Fitness Industry Council of Canada, says that waist-to-hip ratios have long been a tool used by professionals in her sector to help people understand their body weight distribution. She sees BRI as getting “closer to removing weight from the picture, but looking more at where the distribution of weight could be.”
Still, she’d like to see the health and fitness sector move past the mindset that equates health with certain body types and weights. “You could have somebody who exercises a lot who isn’t quote unquote skinny, and someone who doesn’t exercise at all who is quote unquote skinny,” she said.
For Gilbert, the most important measure of health isn’t tied to body composition at all. “Our dose of physical activity is the No. 1 predictor of overall health, and that to me is the measure Canadians should be looking at.” That means, as Health Canada recommends, getting at least 150 minutes of moderate to vigorous exercise weekly.