The American Medical Association’s recent policy decision to reduce and de-emphasise 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, but experts warn this won’t be as easy as it seems.
The new policy states that BMI cut-offs are based on data from white populations and that the metric has been used for “racist exclusion” and caused “historical harm”; that BMI should be used in conjunction with other metrics to help assess fat mass, like waist circumference and body composition, and – of note – it should not be a sole criterion for denying insurance reimbursement.
Reliance on the metric is ubiquitous in how healthcare is delivered and paid for – from surgeries to fertility treatment, from drug approvals to insurance reimbursement, reports STAT News.
“I think the paradigm has been slowly changing for the past five to seven years, 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 has researched the limitations of BMI.
One of the most prominent ways the metric is used is in obesity medicine. In the US, 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 cut-offs 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 cut-offs 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, who believes BMI is still a useful tool for screening and risk stratification.
“Right now, the best tool we have that’s readily available in any clinic is going to be screening based on BMI,” she said. “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.
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 orthopaedic surgery at Stanford University, said some healthcare systems have a policy of not performing hip or knee replacement surgeries on patients with a BMI above 40.
“That interferes with the doctor-patient relationship and 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.
Stat News article – Why it won’t be so easy for medicine to displace BMI (Open access)
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