Obesity needs a new definition beyond BMI, health experts argue

Obesity needs a new definition, argues a global group of health experts.

For over 75 years, obesity has been called a disease by the World Health Organization. But the label is hotly debated. Some say it helps legitimize obesity’s seriousness; others point out that people living with obesity are not always ill.

So a commission of nearly 60 health experts has proposed a definition and diagnostic criteria for clinical obesity: a disease where excess body fat harms a person’s tissues, organs or ability to do daily tasks. The report, published January 14 in the Lancet Diabetes and Endocrinology, also describes preclinical obesity, when surplus body fat does not affect tissues or organs, but may increase the risk for developing clinical obesity, type 2 diabetes, certain cancers and other diseases.

“We are calling for a change — a radical change,” said obesity researcher Francesco Rubino of King’s College London during a Jan. 13 news briefing. “In the context of 1 billion people being classified as having obesity in the world today … no country is rich enough to be able to afford inaccuracy in the diagnosis of obesity.”

Doctors have primarily relied on body mass index, or BMI, to diagnose obesity. A BMI of 30 or above generally classifies adults as having obesity, according to the WHO. (The recommended cutoff is 27.5 in Asians.)

But the metric represents weight divided by height squared rather than a measurement of body fat. BMI, if used, should just be a screening tool accompanied by another metric, like waist circumference, waist-to-hip ratio or waist-to-height ratio, to confirm excess fat, the commission argues. A larger waistline can hint at too much fat surrounding crucial organs, which is particularly dangerous. Two of those body metrics or a body composition scan, which directly measures fat, could work instead of taking BMI into consideration, according to the report.

In addition to those readings, a person should show signs of organ, tissue or whole-body dysfunction before being diagnosed with clinical obesity. The commission specifies 18 symptoms in adults and 13 in children and adolescents, including sleep apnea, high blood pressure, knee pain and difficulties with tasks like bathing.

The proposed definition and diagnostic criteria for clinical obesity are pragmatic and would help clinicians identify who would benefit most from treatment, says cardiologist and obesity researcher Francisco Lopez-Jimenez of Mayo Clinic in Rochester, Minn., who was not involved in the new report. Interventions like GLP-1 drugs, bariatric surgery and lifestyle counseling can be costly for patients, health systems and insurers.

Still, Lopez-Jimenez worries whether preclinical obesity — in which patients may need anything from simple monitoring to weight-loss medications — would be taken seriously. “We have to be careful when we call a condition preclinical,” he says. “If that would lead to less attention, if that would lead to less treatments for those individuals, I would have a problem with that.”

Commission member Fatima Cody Stanford admits that may be a challenge. “Preclinical obesity will struggle, I think, in terms of coverage by insurers. But before, it wasn’t even being acknowledged,” says Stanford, an obesity medicine physician scientist at Massachusetts General Hospital and Harvard Medical School in Boston.

It’s up to individual doctors and health care systems to decide whether to put these guidelines into clinical practice. But the global perspectives that went into the report and a growing movement to better diagnose obesity should help with adoption, Stanford says. “I think that there has been so much pushback at BMI by itself that people are ready to potentially entertain a new way of thinking.”