BMI is a flawed way to measure obesity, experts say. What else works?

Many people with “normal” body mass indexes may still be obese, new research suggests.

The study, which will be presented Friday in Chicago at ENDO 2023, the annual meeting of the Endocrine Society, adds to a growing body of evidence that highlights the flaws of using BMI to measure obesity. Obesity, in the simplest terms, refers to when a person has an excess of fat in the body.

BMI — which is calculated using a person’s height and weight — is the standard way to determine whether someone has obesity or is overweight. A BMI of 30 and above falls into the obese category for most people; 25 to under 30 is considered overweight. It’s ubiquitously used by medical professionals to determine who is at risk for Type 2 diabetes and heart disease and who qualifies for anti-obesity medications and weight loss surgery.

According to the new study, BMI misses a lot of cases of obesity. Researchers looked at data from almost 10,000 U.S. adults collected from 2011 to 2018 and found that almost 36% had obesity based on their BMI. Use of a different measure of obesity — a person’s body fat percentage — put that figure at 74%. The study has not yet been published in a peer-reviewed journal.