Study Questions New Proposal to Redefine Obesity

 

• Of U.S. adults with a BMI indicating obesity, 98.4% also had excess adiposity confirmed by other measures.
• Researchers suggest there may be limited utility to confirming excess adiposity in people with a higher BMI.
• The findings do not apply to certain small subpopulations like athletes.

Virtually all individuals identified as having obesity based on body mass index (BMI) also had confirmed excess adiposity, according to an analysis of National Health and Nutrition Examination Survey (NHANES) data.

Among the 2,225 adults in the study, all under 60 years of age, 39.7% had obesity as defined only by higher BMI, while 39.1% had confirmed excess adiposity when using diagnostic criteria recently laid out by an expert commissionopens in a new tab or window that recommended pairing BMI with at least one other anthropometric index, or direct body fat measurement.

This translated to a 98.4% weighted prevalence of confirmed excess adiposity among adults with a BMI indicating obesity, Michael Fang, PhD, MHS, of Johns Hopkins University Bloomberg School of Public Health in Baltimore, and colleagues reported in a JAMAopens in a new tab or window research letter.

"For nearly all U.S. adults with elevated BMI, there may be limited utility to confirming excess adiposity," they wrote.

While BMI has traditionally been used as the metric for diagnosing obesity for decades, it's recently been falling out of favoropens in a new tab or window, with many healthcare providers calling it a flawed measure of true adiposity. One 2023 studyopens in a new tab or window that also used NHANES data reported that BMI alone only accurately classified 47% as having obesity.

To reduce misclassification, the global commission -- endorsed by more than 75 medical organizations across the world -- released its guide to a more nuanced approach to diagnosing obesity earlier this year.

The commission advised healthcare providers to evaluate the patient's medical history, conduct a physical examination, standard laboratory tests, and additional diagnostic tests if appropriate when assessing excess body fat. While the commission didn't toss out BMI completely, it recommended clinicians pair it with at least one additional anthropometric measure -- like waist circumference, waist-to-hip ratio, or waist-to-height ratio -- or direct fat mass measurement by dual-energy x-ray absorptiometry (DEXA) or bioimpedance.

Additional body measurements weren't considered necessary in patients with a BMI of 40 or higher, though.

"Confirming excess adiposity in routine clinical practice may be challenging," commented Fang and co-authors. "Direct body fat measurement by whole-body DEXA requires specialized equipment and may include out-of-pocket costs for patients."

"Whole-body DEXA may also overestimate body fat, potentially limiting its ability to accurately confirm excess adiposity in patients with elevated BMI," they continued. "Other anthropometric indices (like waist circumference) are convenient and complementary, but technical aspects (e.g., locating anatomical landmarks) may contribute to measurement error, particularly for patients with an elevated BMI."

For their analysis, Fang's group looked at data from the 2017-2018 NHANES survey cycle, which was the most recent nationally representative study with direct body fat measurement by whole-body DEXA and other anthropometric measures. Only adults between the ages of 20 to 59 were included (mean 39.3).

BMI for obesity was defined as 27.5 or greater for Asian adults and 30 or greater for all other participants. Elevated waist circumference and body fat were defined according to race- and sex-specific cutoffs.

Prevalence of confirmed excess adiposity in those with a BMI indicating obesity ranged from 97% to 99.9% across groups stratified by sex, age, and race/ethnicity, suggesting a high level of congruence between the two methods:

• Men: 97%
• Women: 99.9%
• Ages 20-29: 97.8%
• Ages 30-39: 97.5%
• Ages 40-49: 99.5%
• Ages 50-59: 98.8%
• Hispanic adults: 97.3%
• Asian adults: 99.4%
• Black adults: 98.3%
• White adults: 98.6%

Fang and co-authors also pointed out that while certain patent populations, such as athletes, may "warrant further evaluation," their findings indicate these patients "make up a very small portion of the population."

They also highlighted that their findings only apply to adults under the age of 60, "which is an important limitation given the aging of the U.S. population."

Disclosures

The study was supported by grants from the National Heart, Lung, and Blood Institute and the National Institute of Diabetes and Digestive and Kidney Diseases.

Fang reported no disclosures. Another co-author reported receiving personal fees from the American Diabetes Association, the European Association for the Study of Diabetes, and Wolters Kluwer; honoraria for serving as the deputy editor of Diabetes Care; and being a member of the editorial board of Diabetologia.

Primary Source

JAMA

Source Reference: opens in a new tab or windowAryee EK, et al "Prevalence of obesity with and without confirmation of excess adiposity among US adults" JAMA 2025; DOI: 10.1001/jama.2025.2704.

https://www.medpagetoday.com/primarycare/obesity/115178