Annals of Family Medicine: Body Fat Percentage Beats BMI in Predicting 15-Year Mortality Risk Among U.S. Adults Ages 20 to 49

PROVIDENCE, R.I., June 25, 2025 /PRNewswire/ -- A new study published in Annals of Family Medicine finds that body-fat percentage is a stronger predictor of 15-year mortality risk in U.S. adults than body mass index (BMI). Although BMI is widely used in clinics as the standard measure of body composition, it can potentially misclassify muscular individuals as overweight and miss cases of "normal-weight obesity," masking serious metabolic and heart disease risks. The study findings support reexamining how body composition is measured in clinical settings.

Researchers from the University of Florida analyzed data from 4,252 participants in the 1999-2004 National Health and Nutrition Examination Survey (NHANES), a nationally representative sample of non-institutionalized U.S. adults ages 20 to 49. All participants had complete technician measured body composition data, including height, weight and waist circumference. Body fat percentage was assessed by bioelectrical impedance analysis. Records were linked to the National Death Index through 2019. 

After adjusting for age, race and poverty status, the study found:

Numbers in parentheses are the hazard ratio (HR) and its 95% confidence interval (CI).

• Adults with a high body-fat percentage (27% or more in men; 44% or more in women) were 1.78 times more likely to die from any cause than individuals in the healthy body fat range (HR 1.78; 95% CI, 1.28 to 2.47). Adults with a high body-fat percentage were also 3.62 times more likely to die from heart disease (HR 3.62; 95% CI, 1.55 to 8.45).
  
  
• Overweight/obese BMI (25 kg/m² or higher) was not associated with a statistically significant higher risk of death from any cause, compared with adults in the healthy BMI range (HR 1.25, 95% CI 0.85 to 1.84).
  
  
• Adults with a high waist circumference (more than 40 inches in men; more than 35 inches in women) were 1.59 times more likely to die from any cause than individuals in the healthy range (HR 1.59; 95% CI, 1.12 to 2.26). Adults with a high waist circumference were also 4.01 times more likely to die from heart disease (HR 4.01; 95% CI, 1.94 to 8.27).

Historically, it has been difficult to measure body fat percentage in primary care outpatient settings. New bioelectrical impedance devices have the potential to change this; however, implementation details remain to be worked out, as primary care clinics are not yet routinely using them.

"This is a game changer for body composition assessment. Our study is basically a Coke versus Pepsi comparison of a direct and indirect measure of body fat for future mortality risk and a direct measure of body fat percentage that can be done in the office was significantly better," said Arch G. Mainous III, PhD, lead author and professor in the Department of Health Services Research, Management and Policy at the University of Florida.

"The medical community has been aware that BMI has some limitations as a measure of body composition and disease risk. It is an indirect measure of body fat percentage. Direct measures have historically been too expensive and difficult to use in the office. Our study shows that a direct measure of body fat that can be done easily, practically and inexpensively in a doctor's office solves the problems of BMI," said Frank A. Orlando, MD, corresponding author in the Department of Community Health and Family Medicine at the University of Florida.

Article Cited:

Body Mass Index vs Body Fat Percentage as a Predictor of Mortality in Adults Aged 20-49 Years

Arch G. Mainous III, PhD; Lu Yin, PhD; Velyn Wu, MD, MACM; Pooja Sharma, MPH; Breana M. Jenkins, BPH; Aaron A. Saguil, MD, MPH; Danielle S. Nelson, MD, MPH; and Frank A. Orlando, MD

Annals of Family Medicine is an open access, peer-reviewed, indexed research journal that provides a cross-disciplinary forum for new, evidence-based information affecting the primary care disciplines. Launched in May 2003, Annals of Family Medicine is sponsored by six family medical organizations, including the American Academy of Family Physicians, the American Board of Family Medicine, the Society of Teachers of Family Medicine, the Association of Departments of Family Medicine, the Association of Family Medicine Residency Directors, and the North American Primary Care Research Group. Annals of Family Medicine is published online six times each year, charges no fee for publication, and contains original research from the clinical, biomedical, social, and health services areas, as well as contributions on methodology and theory, selected reviews, essays, and editorials. Complete editorial content and interactive discussion groups for each published article can be accessed for free on the journal's website, www.AnnFamMed.org.

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SOURCE Annals of Family Medicine