Obesity: can we cure our dependence on BMI?

Abstract

Obesity remains defined by the flawed metric at the heart of its diagnosis—BMI. Carla Delgado reports on the fresh attempts to move away from this, as weight loss drugs usher in a new age for the obesity crisis The explosion in popularity of weight loss drugs such as semaglutide (Wegovy, Ozempic) and tirzepatide (Zepbound, Mounjaro) has brought a twist to the management of obesity. Patients usually need to exceed a minimum BMI threshold and have at least one weight related health condition to get a prescription for a weight loss drug. And that’s again put a spotlight on the way obesity is defined, measured, and diagnosed. In January 2025, the Lancet Diabetes and Endocrinology global commission on clinical obesity tackled this head on. The report recommended a new framework that moves away from BMI as a singular indicator and instead approaches obesity as a disease spectrum.1 Experts say that not knowing what BMI means can lead to incorrect assumptions about a person’s health and risk of disease. This can affect the quality of care patients receive as well as hinder efforts to prevent and treat obesity.2 BMI has long been considered a quick and easy way to assess whether a person is at a “healthy” weight, but it does not take into account elements like body composition, age, sex, or other lifestyle factors.3 The metric is an indirect measure of body fat that does not indicate the degree to which excess adiposity affects the health of a person.4 BMI was never meant for evaluating health, says Fatima Stanford, an obesity medicine physician at the Massachusetts General Hospital and one of …