New guidelines encourage doctors to move beyond BMI for diagnosing obesity

A new report calls for doctors to stop solely relying on a patient's body mass index to diagnose obesity.

Clinical guidelines published in The Lancet Diabetes & Endocrinology Commission Tuesday say only using BMI to determine if a patient has obesity leads to under-diagnosing people who are ill and over-diagnosing people who don't currently deal with the negative health consequences of obesity.

Instead, the report recommends doctors consider a wider picture of a person's health beyond their BMI.

"This report is fundamentally trying to shift the way of thinking about obesity," Vivek Prachand, a bariatric surgeon and co-director of the University of Chicago’s Digestive Diseases Center, told the Sun-Times. "This report frames the discomfort and ambiguity around conceptualizing obesity as a disease."

For decades, the medical field has relied on BMI, a measurement based on a person's body weight relative to their height, to determine if a patient is underweight, healthy weight, overweight or obese. A BMI between 18.5 and 24.9 is considered "healthy," while a BMI of 30 to 39.9 indicates obesity.

The Lancet commission recognizes obesity as a disease and not just a risk factor. The guidelines set forward new ways to diagnose obesity based on an individual's risk factors, such as their organ health and body fat measurements like their waist circumference, waist-to-hip ratio or waist-to-height ratio.

"BMI works well when you're looking at a population level, but it doesn't say a whole lot about the patient in front of you," Prachand said. "BMI should be used as a screening tool, but not as a definition for a diagnosis."

The commission also introduced two new diagnostic categories of obesity: clinical obesity and pre-clinical obesity. The guidelines say clinical obesity is a chronic disease directly caused by excess fat, while pre-clinical obesity is a condition of excess fat that has yet to cause health complications, but does pose a future risk.

That distinction helps to determine if a person's excess body fat is affecting their health and daily functioning.

Establishing a "pre-clinical" category could help with providing coverage for medications and surgical procedures that treat obesity, Prachand said. Currently, the BMI cutoff is 30 for the increasingly popular GLP-1 drugs like Ozempic.

The guidelines also say that because clinical obesity is a distinct chronic illness, it should not require another disease, like type 2 diabetes, to justify health coverage.

"It does not make sense to wait for the problems to develop before we can treat it," Prachand said.

Obesity is linked to several serious health issues — including diabetes, high blood pressure and high cholesterol — and leading causes of death like heart disease, stroke and certain cancers.

Diagnosing obesity using the new guidelines and treating it before those complications arise can prevent a patient's health from getting worse, Prachand said.

"It just does not sit right that we have to wait to treat someone with diabetes when we could have prescribed something that would have stopped the development of diabetes to begin with," he said.

And it's not just about preventing other health issues, Prachand said. There are quality-of-life impacts that a patient with excess body fat can face. Prachand's patients often complain that obesity restricts their mobility and how they go about their daily life.

"If you don't have high cholesterol or diabetes, we neglect to treat the obesity even though you can’t make it up the stairs," Prachand said. "If you can't play with your kid at the park, there is no blood test for that."