Is B.M.I. a Scam?

It can be a helpful health measure for large groups of people, but it won’t tell you much about yourself.

There are few single measures in health care that seem to carry as much weight as body mass index, or B.M.I. We encounter it not just at doctor’s offices, but with online calculators and smart scales, at gyms and even when determining eligibility for the Covid vaccine. Its formula is simple: Take your weight (in kilograms), and divide by the square of your height (in meters). The result, which slots you into one of four main categories, is meant to describe your body in a single word or two: underweight (B.M.I. less than 18.5), normal weight (18.5 to 24.9), overweight (25.0 to 29.9) or obese (30 or greater). Many feel judged by these categories, given that only about a quarter of adults in the United States can call themselves “normal” on the B.M.I. scale. But after talking with an epidemiologist, two obesity medicine physicians, a health psychologist and a sociologist, none claimed that B.M.I. was a very useful measure of a person’s health. And, in fact, some said they would indeed call it a scam.