Redefining Obesity Would Mean More 'Obese' People

A new study suggests that nearly 70% of US adults would be classified as obese under a revised definition proposed by medical experts. The traditional method, which uses a body mass index (BMI) of 30 or higher, has faced criticism for not distinguishing between fat and muscle. The new criteria proposed in January would establish four routes to that obesity label, per the Guardian: a BMI over 40; those with a high BMI combined with one elevated waist or body fat measurement; someone with two such measures and any BMI; or someone with excess body fat as determined by scans. The proposed definition also introduces two categories: clinical obesity, where illness is present, and pre-clinical obesity, where it is not.

What the new research did was calculate the potential impact of such a change from a numbers perspective. In the study published in Jama Network Open, researchers applied both the old and new standards to data from roughly 300,000 US adults who had joined a health study between 2017 and 2023. Using the traditional BMI cutoff, 43% were considered obese. Under the new definition, that figure jumped to 69%; that's a 60% increase. The figure was 78% among those 70 and older.

Just 678 participants who were obese under the old method would lose that designation if the new standards were applied. But nearly 80,000 people who wouldn't have been considered obese, almost a quarter of participants, would join that group. Per the study, "This rise was driven by inclusion of individuals with anthropometric-only obesity (ie, elevated anthropometrics despite BMI below the traditional obesity threshold)." As study author Dr. Lindsay Fourman tells WCVB: "We already thought we had an obesity epidemic, but this is astounding."