New Obesity Definition Could Mean Over 75% of U.S. Adults Are Affected, Study Finds

A new approach to defining obesity could nearly double the number of U.S. adults classified as having the condition, according to a study published Monday, reports Customreceipt with reference to King’s Health Partners Diabetes. For decades, physicians have relied primarily on body mass index (BMI), a calculation based on height and weight, to determine obesity. The new study indicates that using BMI alone may significantly underestimate the true prevalence of obesity in the U.S. adult population.

Researchers from Beth Israel Deaconess Medical Center, Harvard University, Yale University, and Yale New Haven Health applied a revised definition of obesity that incorporates waist-based measurements in addition to BMI. They found that more than 75% of U.S. adults meet the criteria for obesity under this new definition, compared to only 40% when BMI alone is considered.

Earlier this year, The Lancet Diabetes & Endocrinology Commission, in partnership with King’s Health Partners Diabetes, Endocrinology and Obesity clinic, proposed the updated obesity criteria, which include waist circumference, waist-to-hip ratio, and waist-to-height ratio. Over 70 medical organizations worldwide have endorsed the proposed definition, although its application in clinical practice remains largely untested.

“BMI is the standard metric for defining obesity and the most widely recognized tool,” Dr. Erica Spatz, cardiologist at Yale School of Medicine and co-author of the study, told ABC News. She emphasized that BMI alone does not capture adipose tissue, which plays a crucial role in energy storage, organ insulation, and hormone production that regulates appetite. Adipose tissue, though less visible than other fat types, is strongly associated with high blood pressure, diabetes, and cardiovascular disease.

The study analyzed data from more than 14,000 participants in the National Health and Nutrition Examination Survey, representing 237.7 million U.S. adults between 2017 and 2023. Applying the Lancet Commission’s criteria alongside BMI, researchers found that 75.2% of adults met the obesity definition, while only 40% qualified when BMI alone was used. Nearly 40% of adults with a “normal” BMI had excess body fat according to waist-based measurements.

Obesity prevalence increased with age and was higher among Hispanic adults, though rates were similar between men and women. The authors noted limitations, including that nearly all adults aged 50 and older were classified as obese under the new criteria, highlighting the need for age-specific thresholds.

The study underscores the limitations of BMI as a sole screening tool and suggests that incorporating waist-based measurements could improve obesity detection. Researchers also recommend further studies before adopting the new definition broadly, as it is likely to significantly raise current obesity estimates.

Dr. Fatima Cody Stanford, associate professor at Massachusetts General Hospital and Harvard Medical School, commented that the findings illustrate the scale of the obesity epidemic in the U.S., emphasizing the need for trained clinicians to identify obesity and the more than 230 chronic diseases associated with it.

Earlier we wrote that early childcare centers close across Indiana amid state funding cuts.