People who seek medical treatment for obesity or an eating disorder do so with the hope their health plan will pay for part of it. But whether it\u2019s covered often comes down to a measure invented almost 200 years ago by a Belgian mathematician as part of his quest to use statistics to define the \u201caverage man.\u201d<\/p>\n

That work, done in the 1830s by Adolphe Quetelet<\/a>, appealed to life insurance companies, which created \u201cideal\u201d weight tables after the turn of the century. By the 1970s and 1980s, the measurement, now dubbed body mass index, was adopted to screen for and track obesity.<\/p>\n

Now it\u2019s everywhere, using an equation \u2014 essentially a ratio of mass to height<\/a> \u2014 to categorize patients as overweight, underweight, or at a \u201chealthy weight.\u201d It\u2019s appealingly simple, with a scale that designates adults who score between 18.5 and 24.9 as within a healthy range.<\/p>\n

But critics \u2014 and they are widespread these days \u2014 say it was never meant as a health diagnostic tool. \u201cBMI does not come from science or medicine,\u201d said Dr. Fatima Stanford<\/a>, an obesity medicine specialist and the equity director of the endocrine division at Massachusetts General Hospital.<\/p>\n

She and other experts said BMI can be useful in tracking population-wide weight trends, but it falls short by failing to account for differences among ethnic groups, and it can target some people, including athletes, as overweight or obese because it does not distinguish between muscle mass and fat.<\/p>\n

Still, BMI has become a standard tool to determine who is most at risk of the health consequences of excess weight \u2014 and who qualifies for often-expensive treatments. Despite the heavy debate surrounding BMI, the consensus<\/a> is that people who are overweight or obese are at greater risk for a host of health problems, including diabetes, liver problems, osteoarthritis, high blood pressure, sleep apnea, and cardiovascular problems.<\/p>\n

The BMI measure is commonly included in the prescribing directions for weight loss drugs. Some of the newest and most effective drugs, such as Wegovy<\/a>, limit use to patients who have a BMI of 30 or higher \u2014 the obesity threshold \u2014 or a lower level of 27, if the patient has at least one weight-related medical condition, such as diabetes. Doctors can prescribe the medications to patients who don\u2019t meet those label requirements, but insurers might not cover any of the cost.<\/p>\n

While most insurers, including Medicare, cover some forms<\/a> of bariatric surgery for weight loss, they might require a patient to have a BMI of at least 35, along with other health conditions, such as high blood pressure or diabetes, to qualify.<\/p>\n

With medications, it can be even trickier. Medicare, for example,<\/a> does not cover most prescription weight loss drugs, although it will cover behavioral health treatments and obesity screening. Coverage for weight loss medications varies among private health plans.<\/p>\n

\u201cIt\u2019s very frustrating because everything we do in obesity medicine is based on these cutoffs,\u201d said Stanford.<\/p>\n

Critics say that BMI can err on both ends of the scale, mistakenly labeling some larger people as unhealthy and people who weigh less as healthy, even if they need medical treatment.<\/p>\n

For eating disorders, insurers often use BMI to make coverage decisions and can limit treatment to only those who rank as underweight, missing others who need help, said Serena Nangia<\/a>, communications director for Project Heal<\/a>, a nonprofit that helps patients get treatment, whether they are uninsured or have been denied care through their health plan.<\/p>\n

\u201cBecause there\u2019s such a focus on BMI numbers, we are missing people who could have gotten help earlier, even if they are at a medium BMI,\u201d Nangia said. \u201cIf they are not underweight, they are not taken seriously, and their behaviors are overlooked.\u201d<\/p>\n