BMI remains a reliable indicator of excess body fat in most adults, study finds

Updated on 2025-05-06 00:00:00 0 0

by Justin Jackson, Medical Xpress

Credit: Pixabay/CC0 Public Domain

Johns Hopkins University researchers have found that nearly all adults identified as having obesity based on body mass index (BMI) also had confirmed excess adiposity.

Use of BMI to diagnose obesity has become increasingly controversial. BMI does not distinguish between body fat, muscle, and bone mass, raising concerns that obesity may be overdiagnosed. An expert commission recently recommended that clinical assessments of obesity should be confirmed by direct body fat measurement or BMI and at least one other anthropometric index.

In a research letter, "Prevalence of Obesity With and Without Confirmation of Excess Adiposity Among US Adults, " published in JAMA, researchers analyzed data from a cross-sectional survey to assess obesity prevalence using both BMI and confirmatory measures of body fat.

Researchers evaluated data from 2, 225 adults aged 20 to 59 years participating in the 2017–2018 National Health and Nutrition Examination Survey (NHANES). The survey included standardized measurements of height, weight, and waist circumference, along with whole-body dual-energy X-ray absorptiometry (DEXA) to determine body fat percentages.

Participants with an elevated BMI and either an elevated waist circumference, elevated body fat percentage, or a BMI of 40 or greater were considered to have confirmed excess adiposity. BMI thresholds were adjusted by race and ethnicity, with obesity defined as a BMI of 30 or higher for most participants, and 27.5 or higher for non-Hispanic Asian individuals.

When only considering BMI, 39.7% met the definition of obesity. When using BMI in conjunction with criteria for excess adiposity confirmation, prevalence dropped ever so slightly to 39.1%. Overall, 98.4% of persons with obesity based on BMI had confirmed excess adiposity.

Results were consistent across age, sex, and racial and ethnic groups. Prevalence remained the same when confirmed excess adiposity was defined using either elevated waist circumference or body fat measured by DEXA.

Researchers note that while certain groups, such as athletes, might need individualized assessment, these individuals likely represent a very small portion of the population. For nearly all US adults with elevated BMI, there may be limited need to confirm excess adiposity.

Body fat confirmation in clinical settings may be technically challenging and costly. Findings from this study suggest that for the majority of adults, BMI remains a reliable indicator of excess adiposity, and confirmatory tests may be unnecessary for most cases.

More information: Ebenezer K. Aryee et al, Prevalence of Obesity With and Without Confirmation of Excess Adiposity Among US Adults, JAMA (2025). DOI: 10.1001/jama.2025.2704 Journal information: Journal of the American Medical Association

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