BMI Alone Falling Out of Favor as a Way to Assess Healthy Weight

A shift appears to be occurring in how physicians use the body mass index (BMI) measurement to assess whether someone has obesity, overweight, or underweight.

“We all know BMI is not an adequate measure of health and that [it’s] a flawed system,” said Catriona Hong, a medical student from Glastonbury, Connecticut, and an alternate delegate for the Medical Student Section in the American Medical Association’s (AMA) House of Delegates, on behalf of the section at the AMA’s annual meeting in Chicago earlier this month.

“However, I also urge you to consider how insurance standards subconsciously influence our medical decision-making,” she added. “The use of BMI prevents an enormous amount of individuals from accessing treatment because we are subconsciously using reimbursement as a proxy for medical standards, and that further limits treatments we can provide.”

Ray Lorenzoni, MD, of Woodbridge, Connecticut, an alternate delegate from that state who also spoke at the meeting, noted that “as someone who does normative data research, I can tell you that this is very important. The use of BMI, except to follow a single person — or population trends — over time, is not very useful.”

The delegates were discussing a report from the AMA’s Council on Science and Public Health on clarifying the role of BMI as a measure in medicine. The report concluded that BMI is inaccurate in measuring body fat in multiple groups because it does not account for the heterogeneity across race/ethnic groups, sexes, and age span. The council recommended that because of BMI’s limitations, the AMA should support its use “in conjunction with other valid measures of risk such as, but not limited to, measurements of: visceral fat, body adiposity index, body composition, relative fat mass, waist circumference and genetic/metabolic factors.”

The delegates approved a few changes in the report’s wording. They also referred to the AMA’s Board of Trustees, for more discussion, a proposed addition to the report that stated that “in some clinical circumstances BMI may have utility and that BMI >35 should continue to be used for risk stratification. [The AMA also recognizes] that BMI is a useful tool for population-level surveillance of obesity trends due to its ease of use and … that BMI is useful as an initial screener for metabolic health risks.”

Meanwhile, at ENDO 2023, the annual meeting of the Endocrine Society, which also took place in Chicago at the same time, Aayush Visaria, MD, MPH, of Rutgers Robert Wood Johnson Medical School in New Brunswick, New Jersey, presented results from a study that found that the BMI measure may have misclassified millions of Americans as not having obesity, according to National Health and Nutrition Examination Survey (NHANES) data.

Among over 9,700 adults identified as having obesity according to total body fat percentage estimates using dual-energy x-ray absorptiometry (DEXA) scans, the BMI measure only accurately classified 47% of patients, Visaria and colleagues said. Only 36% of participants had a BMI of 30 or more — the traditional cutoff for obesity — while 74% had obesity according to total body fat percentage, defined as a body fat percentage of 25% or higher in males and 32% or higher for females. On the other hand, when ruling out obesity, BMI and DEXA measures were congruent 95% of the time, he explained.

Certain races and ethnicities had a greater chance of obesity misclassification with BMI than others, the researchers added. Specifically, Asian and Hispanic adults were more likely to have a normal BMI, but have DEXA-confirmed obesity according to their body fat percentage, compared with white adults. Asian and Hispanic adults were also more likely to have a greater proportion of abdominal fat. On the other hand, Black adults with a normal BMI were far less likely to have high body fat percentages and tended to have less abdominal fat.

But it’s not yet time to completely ditch BMI, Visaria noted. “I think BMI still has a lot of use — it’s one of the most accessible measures. It’s simply calculated, it’s trackable, it’s scalable. From a population health standpoint, I do think there are some uses for it.”

“But from a clinical, individual patient level, I think it’s the start of the end. I think BMI should be supplemented with other measures,” he continued.

The shift away from using BMI alone indicates that “we have come a long way” since 2013, when the AMA first declared obesity to be a disease, said Gitanjali Srivastava, MD, medical director for obesity medicine at Vanderbilt University Medical Center in Nashville, Tennessee, in an email to MedPage Today. “There is research to indicate that perhaps body composition and other parameters may be more specific as clinical markers for obesity … in certain ethnicities/races” compared with BMI cutoffs.

However, she added, “Presently, for screening purposes, BMI may be the best indicator. Why? Because it’s free, scalable, easy to do, quick if you know your weight and height.”

“Waist circumference along with neck circumference (to assess for weight-related medical conditions such as sleep apnea) are also powerful indicators for cardiometabolic disease and visceral adiposity. In the clinics, many providers do both — assess for BMI and waist circumference,” Srivastava said.

Fatima Cody Stanford, MD, MPH, director of diversity at Harvard University’s Nutrition Obesity Research Center in Boston, told MedPage Today that the change in strategy regarding BMI “is indeed the right way to be moving in. BMI is a measure that was never derived from medicine or science, but it has been what we’ve utilized in patients like myself — non-Hispanic Black patients — and across wide patient groups, without any attention to the fact that this measure has not been one that reflects the heterogeneity of the population.”

In her own practice, Stanford said she has “always used at least two metrics to evaluate weight status, which include at least a weight and a waist circumference for every single patient, every single visit, both pediatric and adult patients. So I really am excited about the shift.”

Senior Staff Writer Kristen Monaco contributed to this story.