BMI: The mismeasurement of weight and the mistreatment of obesity

BMI: The mismeasurement of weight and the mistreatment of obesity

People who seek medical treatment for obesity or an eating disorder do so in the hope that their health insurance will cover some of the costs. But whether it's covered often depends on a measure invented nearly 200 years ago by a Belgian mathematician as he tried to use statistics to define the "average person."

This work was written in the 1830s by Adolphe Quetelet, appealed to life insurance companies that created “ideal” weight charts after the turn of the century. In the 1970s and 1980s, the measurement now called body mass index was adopted to detect and track obesity.

Now it's everywhere, using an equation - essentially a mass to height ratio – to categorize patients as overweight, underweight or “healthy weight”. It's attractively simple, with a scale that classifies adults between 18.5 and 24.9 as healthy.

But critics - and they are common these days - say it was never intended as a health diagnostic tool. “BMI doesn’t come from science or medicine,” he said Fatima Stanford an obesity medicine specialist and equity director of the endocrine division at Massachusetts General Hospital.

She and other experts said BMI can be useful for tracking population-wide weight trends, but it is inadequate because it does not take into account differences between ethnic groups, and it can label some people, including athletes, as overweight or obese because it cannot distinguish between muscle mass and fat.

Still, BMI has become a standard tool for determining who is most at risk of the health consequences of obesity—and who is eligible for often expensive treatments. Despite the heated debate about BMI the consensus is that people who are overweight or obese are at higher risk for a variety of health problems, including diabetes, liver problems, osteoarthritis, high blood pressure, sleep apnea and cardiovascular problems.

The BMI measurement is commonly included in the prescription instructions for weight loss medications. Some of the newest and most effective drugs, like Wegovy, limit use to patients with a BMI of 30 or higher - the obesity threshold - or lower than 27 if the patient has at least one weight-related condition such as diabetes. Doctors may prescribe the drugs to patients who do not meet these label requirements, but insurers may not cover any portion of the cost.

While most insurers, including Medicare, cover some forms Bariatric weight loss surgery may require the patient to have a BMI of at least 35 and have other health problems such as high blood pressure or diabetes to qualify.

With medication it can be even more difficult. Medicare, for example does not cover most prescription weight loss medications, but does cover behavioral therapies and obesity screenings. Insurance coverage for weight loss medications varies depending on private health insurance.

“It's very frustrating because everything we do in obesity medicine is based on these limits,” Stanford said.

Critics say BMI can err at both ends of the scale, falsely labeling some larger people as unhealthy and people who weigh less as healthy, even if they need medical treatment.

For eating disorders, insurers often rely on BMI to make coverage decisions and may limit treatment only to those considered underweight, missing others who need help, he said Serena Nangia Communications Director for Project Healing a nonprofit organization that helps patients receive treatment whether they are uninsured or have been denied treatment by their health insurance provider.

“Because there is so much focus on BMI values, we are missing people who could have gotten help sooner, even if they have an average BMI,” Nangia said. “If they are not underweight, they are not taken seriously and their behavior is overlooked.”

Stanford said she, too, often argues with insurance companies about who qualifies for obesity treatment based on BMI definitions, especially for some of the newer, more expensive weight-loss medications that can cost more than $1,500 a month.

"I've had patients who were doing well on medication and their BMI fell below a certain level, and then the insurance company wanted to take them off the medication," Stanford said, adding that she questions those decisions. “Sometimes I win, sometimes I lose.”

Although BMI may be useful as a screening tool, it alone is not a good indicator of health, Stanford and many other experts said.

"The health of a person with a BMI of 29 might be worse than that of a person with a BMI of 50 if that person at 29 has high cholesterol, diabetes, sleep apnea or a long list of things," Stanford said, "while the person at 50 just has high blood pressure. Who's sicker? I would say the person with more metabolic disease."

In addition, the BMI Overestimate obesity for tall people and underestimate it for short ones, experts say. And it makes no difference Gender and ethnic differences.

Case in point: "Black women with a BMI between 31 and 33 tend to have better health, even if they are over 30," than other women and men, Stanford said.

In the meantime, various studies, including the long-running Nurses' Health Study, found that Asians had a higher risk of developing diabetes when they gained weight compared to whites and certain ethnic groups. As a result, countries such as China and Japan have set lower BMI limits for overweight and obesity for people of Asian descent.

Experts generally agree that BMI should not be the only measure used to assess patients' health and weight.

“There are limitations,” he said David Creel, a psychologist and registered dietitian at the Bariatric and Metabolic Institute at the Cleveland Clinic. "It doesn't tell us anything about the difference between muscle and fat weight," he said, noting that many athletes may score in the "overweight" category or even end up in the "obese" category because of muscle mass.

Instead of relying on BMI, doctors and patients should consider other factors in the weight equation. You have to be clear about where the weight is distributed. Studies have shown that health risk increases when a person is overweight in the midsection. "If someone has thick legs and most of their weight is in their lower body, it's not nearly as damaging as if they had it in their midsection, particularly their organs," Creel said.

Stanford agrees, saying midsection weight is "a much better indicator of health than BMI itself," with the potential for developing conditions like fatty liver disease or diabetes "directly correlated with waist size."

Patients and their doctors can assess this risk using a simple tool: the tape measure. When measuring just above the hip bone, women should stick with 35 inches or less; Men, 40 inches or less, researchers advise.

New ways to define and diagnose obesity are in the works, including 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 impact insurance coverage and public health interventions.

Stanford has also been studying a way to recalibrate BMI to reflect gender and ethnic differences. It takes into account different groups' risk factors for conditions such as diabetes, high blood pressure and high cholesterol.

Based on her research, she said, the BMI cutoff tends to be lower for men as well as for Hispanic and white women. There would be slightly higher limits for black women. (Hispanic people can be of any race or combination of races.)

“We do not plan to eliminate BMI, but we do plan to develop other strategies to assess health associated with weight status,” Stanford said.

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