Doctors propose new definitions of obesity that would move away from BMI

CBC
·3 min read
Dr. Katherine Morrison, a pediatric endocrinologist and professor at McMaster University in Hamilton, says that when it comes to diagnosing obesity, it's important to move away from thinking just about weight and height and focus on health. (Mike Crawley/CBC - image credit)
Dr. Katherine Morrison, a pediatric endocrinologist and professor at McMaster University in Hamilton, says that when it comes to diagnosing obesity, it's important to move away from thinking just about weight and height and focus on health. (Mike Crawley/CBC - image credit)

Major medical groups are proposing a major change to how doctors diagnose obesity.

In Tuesday's issue of The Lancet Diabetes & Endocrinology, 58 international experts across a range of medical specialties and people with lived experience released a report proposing a new definition and diagnostic criteria for clinical obesity. They say the current medical approaches to diagnose obesity don't reliably assess an individual's health.

The international Commission on Clinical Obesity which proposed the new definitions called it a nuanced approach. Their report includes 18 diagnostic criteria for clinical obesity in adults and 13 criteria for children and adolescents.

"It's very important that we move away from thinking just about weight and height and focus on health," said Dr. Katherine Morrison, one of the authors of the global commission and a pediatric endocrinologist and professor at McMaster University in Hamilton.

Traditionally, obesity has been defined by size, specifically the body mass index (BMI), a ratio of weight to height. Because BMI doesn't take into account the difference between fat and lean mass, it can be misleading and result in people who are fit and healthy being misclassified as overweight. Both the Lancet report and a 2019 British Journal of Cardiology study outlined examples of such misclassifications, including heavyweight champion boxers who have large muscle mass.

Some people tend to store excess fat at the waist or in and around organs, such as the liver and heart or the muscles, which is associated with a higher risk to health compared to having extra fat stored under the skin elsewhere like the arms or legs, the Lancet report said. But BMI alone doesn't take into account fat distribution, which can contribute to misdiagnosis of obesity under the traditional definition.

The report's authors now define "clinical obesity" as a chronic disease associated with ongoing signs or symptoms of reduced organ function, such as sleep apnea or heart failure, due to obesity alone. People who have a significantly reduced ability to take part in activities such as bathing, dressing and continence directly due to excess body fat also meets the new definition, according to the report.

Morrison says the new definition of obesity "is very important to enable folks to get the treatment that they need," which can include lifestyle changes, medication and surgery.

WATCH | Why experts say BMI can be misleading:

Moving away from judgment

According to global estimates previously published in the Lancet, more than one billion people worldwide are estimated to be living with obesity.

Dr. Sean Wharton, medical director of the Wharton Medical Clinic for Weight Loss in Burlington, Ont., agrees with the proposed changes. He was not involved in the new definitions, which move away from BMI cutoffs based mainly on white, European males.

"Physicians, scientists have known that obesity is more than just body size," Wharton said. "It's about the inflammation in the adipose tissue or fat cells."

Wharton hopes that reframing obesity as a disease will help move away from people with larger body sizes being judged for their weight.

WATCH | Weight-loss chain shuts down: 

Diabetes Canada, American Heart Association and Take Off Pounds Sensibly (TOPS), a non-profit weight-loss support group, are among those endorsing the new definitions.

Francesco Rubino, the chair of the Commission on Clinical Obesity and a professor at King's College London, told reporters use of GLP-1 class of drugs to treat obesity, such as Wegovy and Ozempic, was not their focus.

However, he said that if the clearer diagnoses proposed by the report were to be adopted by health-care systems worldwide, it could help doctors decide when best to prescribe them based on individual risk, and result in health insurers considering coverage for the drugs for clinical obesity alone. Many insurers currently require another related condition to be present, like diabetes.

"We hope this leads to a change in practice, and maybe even before that, a change in mindset," said Rubino, who consults for makers of obesity drugs and medical devices.

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