News: New obesity criteria would capture over a quarter of U.S. adults with normal BMI

Over a quarter of United States adults with a normal body mass index (BMI) met recently proposed criteria for clinical obesity, a national cross-sectional study found.

The researchers analyzed National Health and Nutrition Examination Survey (NHANES) responses from 5,642 nonpregnant U.S. adults ages 20 and older between 2021 and 2023. Among adults with a BMI in the normal range of 18.5-24.9, an adjusted 26.1% had clinical obesity according to the Lancet Diabetes & Endocrinology commission criteria. This criterion is defined by abnormal anthropometric measurements with organ or physical dysfunction, researchers led by Brian Lee, MD, of the University of Southern California in Los Angeles, reported.

According to the commission, clinical obesity is considered a state of ongoing illness involving tissue or organ dysfunction caused by excess adiposity. Clinical obesity prevalence jumped by 50.3% for those in the overweight BMI category, 65.6% for those with class I obesity, 77.8% for class II obesity, and 85.3% for class III obesity.

The Lancet commission pitched the new diagnostic framework in January 2025, advocating for a more nuanced approach than provided by the ratio of height to weight that defines BMI. The commission proposed that clinicians verify obesity status by using other anthropometric measures, such as waist circumference, waist-to-hip ratio, or waist-to-height ratio, or using direct fat measurements via dual-energy x-ray absorptiometry (DEXA) scans or bioimpedance.

Lee’s research group found that 78% of adults had excess adiposity if defined by using two or three abnormal body measurements. This resulted in nearly double the prevalence detected by traditional BMI-based definitions, Lee’s team found. “These findings suggest that incorporating multiple anthropometric indicators may detect persons with physiologic consequences of excess adiposity who would otherwise be missed using BMI alone,” they wrote.

Defining obesity solely on BMI has come under fire in recent years despite being widely used for decades, as it may over- or underestimate body fat.

“BMI is problematic because it does not specifically measure body fat and instead reflects total body weight, which includes muscle and bone," Lee said in a statement. "So a muscular person can have a very high BMI but not have excess fat, while someone without much muscle can have a normal BMI but have excess fat causing health problems.”

While Lee's team advocated for moving beyond BMI, they acknowledged that future studies need to determine whether screening via the commission's proposal actually improves health outcomes or simply increases overdiagnosis and overtreatment.

“Given that current clinical guidelines for screening of obesity-related medical conditions and thresholds for treatment (for example, with incretins) are based on BMI, these findings, if adopted, have important implications for screening and clinical interventions,” they noted. “Further studies should assess the safety and efficacy of such interventions among persons with clinical obesity without elevated BMI.”

Editor’s note: To read the full study, click here. To read additional coverage from TechTarget, click here.