BMI: The mismeasurement of weight and the misuse of obesity

People who seek treatment for obesity or an eating disorder expect that their health plan will pay for part of it. But whether it’s covered often comes down to a measure invented nearly 200 years ago by a Belgian mathematician as part of his quest to use statistics to define the “average person.”

Adolphe Quetelet’s work in the 1830s appealed to life insurance companies, who developed “ideal” weight tables after the turn of the century. In the 1970s and 1980s, the measure, now known as the body mass index, was adopted to measure and track obesity.

Now it’s everywhere, using an equation — essentially a mass-to-height ratio — to classify patients as overweight, underweight or “healthy weight.” It’s strikingly simple, a scale that designates adults who score between a healthy range of 18.5 and 24.9.

But critics — and they are widespread these days — say it was never meant to be a health diagnosis tool. “BMI doesn’t come from science or medicine,” says Dr. Fatima Stanford, an obesity medicine specialist and director of equity in the endocrine department at Massachusetts General Hospital.

He and other experts say BMI can be useful in tracking population-wide weight trends, but it falls short because it fails to account for differences between ethnic groups, and it can mark some people, including athletes, as overweight or obese because it doesn’t differentiate. . between muscle mass and fat.

Still, BMI has become a standard tool for determining who is most at risk for the health consequences of being overweight—and who qualifies for often expensive treatment. Despite the great controversy surrounding BMI, the consensus is that people who are overweight or obese are at higher risk for many health problems, including diabetes, liver problems, osteoarthritis, high blood pressure, sleep apnea, and cardiovascular problems.

BMI measurements are commonly included in weight loss medication prescriptions. Some of the newer and most effective drugs, such as Wegovi, limit use to patients with a BMI of 30 or higher — the obesity threshold — or a lower level of 27, if the patient has at least one weight-related medical condition, such as diabetes. Doctors can prescribe the drug to patients who don’t meet these label requirements, but insurers may not cover any costs.

Although most insurers, including Medicare, cover some types of bariatric surgery for weight loss, patients with other health conditions such as high blood pressure or diabetes must have a BMI of at least 35 to qualify.

With drugs, it can be more complicated. Medicare, for example, does not cover most prescription weight loss drugs, although it will cover behavioral health treatments and obesity screenings. Weight loss drug coverage varies among individual health plans.

“It’s very frustrating because everything we do in obesity medicine is based on this cutoff,” Stanford said.

Critics say BMI can err on both ends of the scale, wrongly labeling some large people as unhealthy and underweight people as healthy, even if they need treatment.

For eating disorders, insurers often use BMI to make coverage decisions and may limit treatment to those who are underweight, absent others who need help, said Serena Nangia, director of communications for Project Hill, a nonprofit that helps patients get treatment, whether they are . Not insured or denied care through their health plan.

“Because there’s such a focus on BMI numbers, we’re missing people who could have gotten help earlier, even if they had a moderate BMI,” Nangia said. “If they’re not underweight, they’re not taken seriously and their behavior is ignored.”

Stanford said she also often fights with insurance companies to qualify for overweight treatment based on BMI definitions, especially for some of the newer, more expensive weight-loss drugs, which can cost more than $1,500 a month.

“I’ve done a good job of medicating patients and their BMI drops below a certain level, and then the insurance company wants to stop their medication,” Stanford said, adding that he challenges those decisions. “Sometimes I win, sometimes I lose.”

While potentially useful as a screening tool, BMI alone is not a good arbiter of health, Stanford and many other experts say.

“A person with a BMI of 29 may be in worse health than someone with a BMI of 50 if that person at 29 has high cholesterol, diabetes, sleep apnea or a laundry list of things,” Stanford said, “A person at 50 just has high blood pressure. Which one is sicker? I’d say the person is more metabolically ill.”

Additionally, BMI can Overestimate obesity for tall people and underestimate it for short ones, experts say. And that doesn’t account for gender and racial differences.

For example: “Black women with a BMI between 31 and 33 are in better health than those with a BMI above 30” compared to other women and men, Stanford said.

Meanwhile, several studies, including the long-running Nurses’ Health Study, found that Asians had a higher risk of developing diabetes due to weight gain than whites and some ethnic groups. As a result, countries such as China and Japan have set lower BMI overweight and obesity thresholds for people of Asian descent.

Experts generally agree that BMI should not be the only measure for evaluating patients’ health and weight.

“It has its limitations,” says David Creel, MD, a psychologist and registered dietitian at the Cleveland Clinic’s Bariatric and Metabolic Institute. “It doesn’t tell us anything about the difference between muscle and fat weight,” he said, adding that many athletes may score in the overweight category, or even land in the obese range due to muscle bulk.

Regardless of BMI, physicians and patients should consider other factors in the weight equation. Being aware of where the weight is distributed. Studies have shown that health risks increase if a person carries excess weight in the midsection. “If someone has thick legs and most of their weight is in the lower body, it’s not nearly as damaging if it’s in their midsection, especially around their limbs,” Creel says.

Stanford agrees, saying that midsection weight is a “much better proxy for health than BMI,” with the likelihood of developing conditions like fatty liver disease or diabetes being “directly correlated with waist size.”

Patients and their doctors can use a simple tool to assess this risk: the tape measure. Measured just above the hips, women should be 35 inches or less; For men, 40 inches or less, the researchers suggest.

New ways of defining and diagnosing obesity are in the works, with a panel of international experts convened by the prestigious Lancet Commission, said Stanford, a member of the group. Any new criteria ultimately approved could not only help inform physicians and patients, but also affect insurance coverage and public health interventions.

Stanford also studied a way to adjust BMI to reflect gender and racial differences. It covers several groups of risk factors for conditions such as diabetes, high blood pressure and high cholesterol.

Based on his research, he said, the BMI cutoff would be lower for men as well as Hispanic and white women. It would shift the cutoffs slightly higher for black women. (Hispanic people can be any race or color combination.)

“We don’t plan to eliminate BMI, but we do plan to develop other techniques to assess health related to weight status,” Stanford said.

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