The policy that the American Medical Association adopted this week to de-emphasize the use of BMI is part of a growing movement away from the single, weight-based metric and toward a broader way of assessing health risk through multiple factors.
Yet it will take more than the giant physician group to displace the use of the body mass index throughout medicine. Reliance on the metric is ubiquitous in the ways health care is delivered and paid for — from surgeries to fertility treatment, from drug approvals to insurance reimbursement.
“I think the paradigm has been slowly changing for the last five to seven years, slowly, and the statement might actually speed it up so it is more widely accepted,” said Francisco Lopez-Jimenez, a cardiologist at the Mayo Clinic who’s researched the limitations of BMI. “This was an unequivocal statement. They were not shy.”
Still, “paradigm changes take more than a single statement,” he said. “A paradigm change requires different people, different societies, you have to hear this over and over.”
The AMA’s new policy states that BMI cutoffs are based on data from white populations and that the metric has been used for “racist exclusion” and has caused “historical harm.” BMI should be used in conjunction with other metrics to help assess fat mass, like waist circumference and body composition, and — of note — BMI should not be a sole criterion for denying insurance reimbursement, the policy states.
One of the most prominent ways the metric is used is in obesity medicine. Weight loss drugs, including the highly popular Wegovy, are approved and often reimbursed only for people who have a BMI over 27 with comorbidities or with a BMI over 30. Bariatric surgery is often covered only for people who have a BMI over 35.
But those cutoffs are arbitrary, and they restrict care for patients who don’t meet the exact BMI threshold yet have metabolic issues that need addressing, Lopez-Jimenez said.
The difficulty in changing the status quo is that “the most robust science we have is around BMI as a measure,” said Angela Fitch, president of the Obesity Medicine Association. Trials and research on obesity interventions have all been conducted around BMI cutoffs since they’re easy numbers to collect.
“We’re already moving away from [BMI] philosophically, and that’s good,” said Fitch, who’s also chief medical officer at knownwell, a company that treats people with obesity. But “we need the science to catch up with the movement,” she said, adding that studies to test other metrics are lengthy and difficult to conduct.
The reality of how much reliance there is on BMI was a concern for another obesity medicine doctor, Carolynn Francavilla Brown. As the AMA discussed the new policy at its meeting here this week, she spoke up in favor of including language saying that BMI is still a useful tool for screening and risk stratification. But ultimately, AMA members voted that the language needed further study and discussion, so it wasn’t included in the final policy.
“Right now, the best tool we have that’s readily available in any clinic is going to be screening based on BMI,” Francavilla Brown said in an interview. “We need better things. [The AMA policy] is a push in the right direction, but we also have to accept the reality of what we have right now.”
BMI is entrenched in other areas of medicine, too. Patients with eating disorders, for example, may be denied care or coverage if they don’t have a low enough BMI.
Reilly Bealer, an incoming medical resident who worked with other students to push the AMA to look into a BMI policy, experienced this barrier herself. When she had an eating disorder about three years ago, her primary care doctor didn’t refer her to receive eating disorder treatment since her BMI wasn’t below 18. She eventually found treatment on her own, but it was delayed.
“I felt pretty disheartened,” she said. “It can be very challenging when somebody cries out for help and is seeking help, but they don’t receive the help that they feel they need.”
The metric can affect who is approved for fertility treatments. In a 2019 survey of OB-GYN subspecialists, the majority supported upper limit BMI cutoffs.
It’s used to assess surgery eligibility as well. Nicholas Giori, a professor of orthopedic surgery at Stanford University, said some health care systems have a policy of not performing hip or knee replacement surgeries on patients with a BMI above 40.
“That basically really interferes with the doctor-patient relationship and it doesn’t give surgeons or patients any opportunity to adjust decision-making based on individual situations,” Giori said. For example, a patient could have a BMI over 40, but their fat is concentrated in their abdomen and not in their legs, so a knee replacement surgery could be fairly straightforward.
“BMI is this really easy number to calculate but oversimplifies preoperative risk assessment,” he said.
A high BMI has also been cited as a reason to deny gender-affirming surgery for some patients.
Loren Schechter, a plastic surgeon at Rush University, said that he personally stopped using a BMI cutoff to assess genital surgery eligibility years ago, and now considers a combination of factors including comorbidities and body composition.
“I think the trend is moving away from BMI, but these entrenched issues don’t fade away easily,” he said. “Unfortunately, oftentimes you need a lot of literature and experience to do away with some of these things that have been ingrained in the system for a while.”
Interestingly, it appears that people outside of medicine have been more skeptical of BMI than those in the medical community, said Lopez-Jimenez, the Mayo Clinic cardiologist. When he presented his early research on the shortcomings of BMI, doctors would be shocked, while people outside of medicine thought it made sense, he said.
“Ten years ago, you would not even dare to challenge the validity of BMI,” he said. After the AMA policy, “I really hope clinicians that were reluctant to accept this are more open to this.”
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