Obesity should be assessed in a way that goes beyond the standard measure of body mass index, or BMI, according to a new definition of the condition published by an international panel.
His report, published Tuesday in The Lancet Diabetes & Endocrinology journal, advocates focusing on the amount of body fat and what medical complications a person has, rather than just their weight.
If the guidelines are widely accepted, they could change doctors’ perceptions of who should be treated for obesity. They could also affect the use of prescription drugs that treat obesity, such as Wegovy and Zepbound. The new definition of obesity was supported by 76 organizations around the world.
The committee suggested that instead of continuing the current use of BMI – as a way of defining obesity – it should be a screening tool to determine who should be tested for excess body fat.
The commission said that people who have a BMI above 25 and have too much fat, but who are otherwise healthy, should be left alone. They should be monitored and advised to stop gaining weight and possibly lose a little.
Their condition would be called preclinical obesity.
Other people with any of the 18 medical conditions caused by obesity – 13 for children and adolescents – require treatment to improve their health and prevent serious organ damage. Conditions include shortness of breath, heart failure, pain in the hips or knees, metabolic abnormalities, and malfunctioning organs.
Their condition would be called clinical obesity.
The group said those with a BMI of 40 or higher are clinically obese based on their BMI alone – there is no need to estimate their body fat.
The commission said it did not know the prevalence of the two types of obesity.
The simplest way for doctors to see if someone has excess body fat is to wrap a tape measure around a person’s waist, the group said. If a woman’s waist is greater than 34.6 inches, she most likely has too much fat. For a man, the waist threshold would be at least 40 inches.
Other tools for healthcare professionals include waist-to-hip ratios, waist-to-height ratios, or a DEXA scan, a type of X-ray.
The commission’s 58 experts spent years on the report, meeting regularly online. Instead of thinking about obesity as a disease, they wanted to evaluate it in a different way, said the president of the commission, Dr. Francesco Rubino, a bariatric surgeon from King’s College London. (Dr. Rubino consults with manufacturers of obesity drugs and medical devices.)
The commission’s approach echoes that of the American Heart Association, which endorsed the report.
“We have struggled with imprecise methods for defining what is a poor weight,” said Dr. Mariell Jessup, chief scientific and medical officer at the association. “How do you define ideal weight, and how do you define unhealthy weight?”
“We have been asked many times Do you think obesity is a chronic disease? We were unhappy saying ‘yes’ or ‘no,’” she said. “We think it’s more nuanced.”
Rebecca Puhl, deputy director of the University of Connecticut’s Rudd Center for Food Policy and Health, said she sees the commission’s approach as “an attempt to reduce some of the misconceptions about obesity that could potentially reduce stigma.”
“Obesity is still seen as a character flaw rather than a complex medical condition,” she said.
But it may be difficult for new definitions to enter common usage.
For years, experts have complained about relying on BMI to define overweight and obesity.
The index is easy to measure — only a person’s height and weight are needed. It soon became the standard for defining whether people were undernourished, overweight or obese.
And BMI has been identified as a major risk factor for diabetes, heart disease, cancer and other conditions, said Dr. David M. Nathan, professor of medicine at Harvard and founder of the diabetes center at Massachusetts General Hospital.
He added that a large waist is also a risk factor. But unlike BMI, waist measurements are often inaccurately performed in medical facilities.
It is unrealistic, said dr. Nathan, “to say the whole world is going to change to this.”
It is equally unrealistic, he continued, to say that obesity should not be treated until complications arise. “As they would have it, you wouldn’t treat hypertension until a person had a stroke,” said Dr. Nathan.
Although not all obese people develop serious health problems, “the number of those who do not develop some kind of weight-related complication is quite small,” added Dr. Nathan.
The use of the new standard could also have implications for new obesity drugs and other drugs coming to market. They are so expensive that some health systems that initially covered them for people with obesity — defined by their BMI — decided they could no longer afford it.
But dr. David Cummings, a panel member and obesity expert at the University of Washington, suggested they could be limited to patients diagnosed with clinical obesity.
The needs of that group, he said, “are more compelling.”