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BMI is an ‘imperfect’ way to measure health. But replacing it is complicated

Vishal Gentle isn’t the avid gym-goer he was before his daughter was born a few months ago.

But the new dad said he does what he can to stay active — carrying the baby up and down stairs to get a bit of a workout, lots of walking and using a stand-up desk. 

Gentle said he feels healthy, but according to the body mass index, or BMI, he’s overweight.

“Honestly, I don’t feel overweight. I mean, except a little bit near my waist. But like I’m fully active. I can do anything and everything,” he said during an interview in his Toronto home. 

Gentle isn’t alone when it comes to questioning if his BMI is an accurate way of measuring health. The BMI is under growing scrutiny — both for its usefulness as a measure of health and its problematic origins.

BMI is calculated by dividing weight in kilograms by height in metres squared. The result can be compared to the BMI chart, easily found all over the internet, social media and in doctors’ offices, that instantly advises the user if their result is underweight, normal, overweight or obese.

Last month, the American Medical Association (AMA) formally recognized BMI’s shortcomings and created a new policy advising caution when using it. 

In a news release in June, the AMA warned that the BMI is an “imperfect way to measure body fat in multiple groups given that it does not account for differences across race/ethnic groups, sexes, genders, and age-span.”

WATCH | The problem with BMI: 

bmi is an imperfect way to measure health but replacing it is complicated

Using BMI to assess your health can be misleading, experts warn

5 days ago

Duration 2:03

The American Medical Association warns BMI or body mass index can be a misleading health indicator, and some health-care experts instead favour things like waist circumference. Health Canada still promotes BMI on its website but says the tool is imperfect.

It also notes that the BMI, which dates back to the 19th century, has a problematic foundation.

“Under the newly adopted policy, the AMA recognizes issues with using BMI as a measurement due to its historical harm, its use for racist exclusion, and because BMI is based primarily on data collected from previous generations of non-Hispanic white populations,” the news release states.

The AMA encouraged clinicians to use other factors such as waist circumference, fat distribution and genetic factors when assessing a patient’s health. 

Growing criticism

The AMA’s position is the latest in mounting criticism of the BMI. 

The inability to distinguish between mass created by fat, muscle and bone has been noted as a shortcoming by experts and health authorities, as is the lack of distinction for where fat is distributed on the body. 

They note abdomen fat can be a risk factor for conditions like diabetes and heart disease, while hip and thigh fat is less associated with health issues.

A man smiles at the camera
Dr. Sanjeev Sockalingam is the scientific director of Obesity Canada. The organization’s latest practice guidelines leave BMI out of the definition of obesity. (Obesity Canada)

Dr. Sanjeev Sockalingam, the Toronto-based scientific director of Obesity Canada, said he hopes the AMA’s position accelerates work to find better ways for assessing health, and specifically for evaluating obesity as a medical condition. 

“I’m hoping that this will actually spawn a bit more research as well in this area, which I think is much needed given all the challenges and issues that we’ve identified with BMI,” he said.

Obesity Canada’s latest practice guidelines leave BMI out of the definition of obesity, and instead describe it as a chronic medical condition that results in disability and impairment.

Why has the BMI stuck around?

Still, BMI calculators are easily found on websites for organizations like the Canadian Cancer Society and Diabetes Canada.

Health Canada promotes use of BMI and has the chart on its website, but notes the measure shouldn’t be used by people under age 18, or those who are pregnant or lactating. 

The agency has recommended using BMI along with measuring waist circumference since 2003, spokesperson Nicholas Janveau said in an email.

“While BMI has some limitations, it still tends to be the preferred measure of excess body fat for population-level surveillance and epidemiologic studies because of its simplicity and the ease with which it can be estimated,” Janveau said.

Despite all of Sockalingam’s misgivings about BMI, he said it can’t be abandoned just yet because it’s deeply integrated into clinical trials and other aspects of health care.

“We don’t want to remove it right now without anything to replace it because it’s been so difficult to get people to recognize obesity as a chronic medical condition and to think about patient-centred approaches and treatments that are now emerging for people living with obesity,” he said.

He advises people to think of BMI as a high-level screening tool, but not to rely on it for diagnosing an individual.

What’s the alternative?

Dr. Sonia Anand, a vascular medicine specialist at McMaster University in Hamilton, Ont., said she agrees that it would be difficult to untangle BMI from its place in clinical settings, research and the weight-loss industry.

She knows it won’t go away any time soon, but said she’d like to see it replaced by waist circumference as the go-to free, simple measurement.

“It is entrenched in our way of thinking. But it is now reasonable, a good time for different health-care practitioners, agencies, trialists and individuals to start measuring waist circumference and use that together with body weight,” Anand said.

A doctor stands in a clinic room
Dr. Sonia Anand, a vascular medicine specialist at McMaster University, says continuing to rely on BMI for people with different backgrounds and lifestyles means risking missing signs to test for metabolic changes. (Turgut Yeter/CBC)

Anand has done research into how South Asian people experience metabolic changes such as increases in blood sugar, blood pressure and cholesterol at a lower cut off point than white Europeans do.

She said continuing to rely on BMI for people with different backgrounds and lifestyles means risking missing signs to test for metabolic changes, or could lead to a person with a lot of muscle mass and a high BMI being wrongly advised to lose weight. 

By itself, waist circumference isn’t the gold standard in assessing health, either, Anand said, but she added it does a better job of assessing whether someone has excess body fat in a specific area that can increase the risk of health issues.

A holistic approach

When it comes to diagnosing and treating obesity, Sockalingam said he would like to see more holistic assessment.

“Ultimately we want to look at how obesity is impacting an individual in terms of their day-to-day living, their functioning and their co-occurring conditions, whether it be physical or mental health,” he said.

Anand and Sockalingam agree that even if discontent with BMI as a measurement of health grows, it’ll take quite a while for widespread change to happen. Sockalingam said he hopes that people who hear about the problems with BMI will be empowered to ask their health-care practitioners for different kinds of assessments. 

Vishal Gentle said he has had those conversations with his family doctor in Toronto, who told him he’s not overweight.

He said it’s important to him to keep a close eye on his health because his father died at age 67 during cardiac arrest. 

Gentle said his father carried weight on his belly and so his doctor’s advice to focus on eating well, exercising and keeping an eye on waist circumference makes sense to him. 

“As long as I’m able to feel good and carry on my day-to-day, I have no issues,” he said.

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