Why BMI is an unreliable tool when diagnosing obesity

First at Five looks at the call to stop using body mass index to diagnose obesity.

One in three Canadians are overweight or living with obesity, but there are gaps when it comes to diagnosing it.

Body Mass Index (BMI), which relies on a person’s height and weight, has long been used as a tool.

“Right now, there’s an overreliance on BMI,” said Kara Evers, a nurse practitioner and coordinator for the Halifax bariatric surgery program.

“It doesn’t differentiate between lean muscle and fatty tissue. The classic example of this is a body builder who has a higher weight to height ratio, and has a higher BMI, but is clearly not living with obesity.”

Doctors around the world are now proposing changes to how obesity is diagnosed, with a shift away from BMI.

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Several other factors are already looked at for patients in Halifax using Obesity Canada recommendations.

“We collect waist circumference. We collect blood pressure. We do a complete set of labs. We look at other comorbidities that are impacting obesity. We look at whether patients have tried certain medications,” said Evers.

Nova Scotia has the second highest rate of obesity in Canada, but Evers said there is not a lot of funding.

“Patients are continuously referred to our clinic, and yet we just don’t have the resources to be able to do the number of surgeries that are required,” Evers said.

Evers said there are just under 200 surgeries in the province each year, and more than 2,000 patients on the waitlist.

Clinical obesity definition

According to the authors of the report in medical journal The Lancet, clinical obesity is now defined as a chronic disease.

“People are entitled to their own opinions, but not their own facts, and the facts tell us this is a chronic relapsing disease. This is something people living with obesity are going to need a continuum of care,” said Obesity Canada executive director Lisa Schaffer.

Obesity Canada has called for these changes for a long time.

“That’s what this framework also bring in is understanding that somebody could be in a bigger body, but be functionally healthy,” said Schaffer.

“This is a really interesting shift and a really important moment right now because it introduces personalized care in a new way.”

When trying to get healthy, registered dietician Nicole Marchand said it’s about looking at body fat percentage, not body mass index.

“It’s the actions they do day to day that can help with that, so for example, you need to move your body every single day. I recommend at least 30 minutes of physical activity a day,” said Marchand. “You also want, in my opinion, a mostly whole foods diet. So your meals are based on whole foods, animal products and plant-based products, and your meals are balanced, high in protein, and lots of colour, lots of fiber.”

While the recommendations around BMI are regarded as a positive step, there are still barriers for those seeking care.

“The other hope in defining obesity as a clinical chronic disease is that it will help to overcome some of the weight bias that is so prevalent, not just in society but in the health care field,” said Evers. “This is the biggest obstacle to care, so if we continue to believe that obesity is a lifestyle choice and continue to blame and shame patients, then patients are never going to receive the necessary and timely access to care that they need.”