Body Fat Percentage Outranks BMI as a Predictor of Long-Term Mortality

Body mass index (BMI) is a common measure of body composition; however, research suggests that this measure is flawed, often misclassifying muscular individuals as overweight and failing to identify “normal-weight obesity”—a condition that relates to significant metabolic and heart disease risks. In a study conducted by researchers from the University of Florida, the investigators compare BMI to body fat percentage as predictors of 15-year mortality in adults ages 20 to 49 years to better understand body composition and identify an accurate risk assessment.^1,2

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BMI, Body Fat Percentage & Normal Weight Obesity

According to the CDC, BMI is a calculated measure of weight relative to height, categorized as underweight, healthy weight, overweight, and obese. The measurement is an estimate of body fat that can help identify a patient’s risk for certain diseases that can occur with overweight and obesity. Looking at an individual’s medical history, health behaviors, physical exam findings, and laboratory findings on top of their BMI could give health care providers a complete picture of their patients’ health. For example, excess weight could increase an individual’s risk for high blood pressure, high cholesterol, and other chronic conditions.^1,3

Body fat percentage is measured by determining how much of an individual’s weight is fat, often measured by the circumference of the waist. Typically, greater than 35 inches for women and greater than 40 inches for men indicates more abdominal fat that places those individuals at an increased risk of health issues.⁴

Individuals with normal-weight obesity—defined as having a normal BMI but high body fat mass—are also underdiagnosed and face high rates of morbidity and mortality due to their increased risk for cardiometabolic conditions. This emphasizes the flaws in BMI measurements, highlighting the need for further assessments.⁵

Mortality Risk: BMI vs Body Fat Percentage

Researchers analyzed data from a total of 4525 unweighted individuals who were included in the 1999 to 2004 National Health and Nutrition Examination Survey (NHANES), linked to the National Death Index, indicating a nationally representative cohort of US adults. Among the 4525 individuals, 1431 were female and 2821 were male.^1,2

Healthy ranges were defined for BMI, body fat percentage, and waist circumference. Specifically, healthy BMI was between 18.5 and 24.9 kg/m², while healthy body fat percentage was below 27% for men and 44% for women. A healthy waist circumference was defined as 40 inches or less for men and 35 inches or less for women, as values at or above these thresholds were considered unhealthy.^1,2

In the analysis, the 15-year mortality risk for BMI, body fat percentage, and waist circumference was computed. The results demonstrated that individuals with a high body fat percentage were 1.78 times more likely to die from any cause than individuals in the healthy body fat range (hazard ratio (HR) 1.78; 95% CI, 1.28 to 2.47) and 3.62 times more likely to die from heart disease (HR 3.62; 95% CI, 1.55 to 8.45). Similarly, a large waist circumference was linked to a 1.59 times greater risk of death from any cause (HR 1.59; 95% CI, 1.12 to 2.26) and a 4.01 times greater risk of death from heart disease (HR 4.01; 95% CI, 1.94 to 8.27). However, individuals with a BMI of 25 kg/m² or higher, classified as overweight or obese, were not found to be a statistically significant predictor of higher mortality risk.^1,2

The findings suggest that body fat percentage and waist circumference are both linked with a 15-year mortality, meaning that body fat percentage is a better predictor of mortality risk in young adults compared with BMI.^1,2

REFERENCES

1. Mainous A, Yin L, Sharma P, et al. Body Mass Index vs Body Fat Percentage as a Predictor of Mortality in Adults Aged 20-49 Years. Annals of Family Medicine. July 2025. doi: https://doi.org/10.1370/afm.240330

2. Body fat percentage beats BMI in predicting 15-year mortality risk among U.S. adults ages 20 to 49. EurekAlert! News release. July 28, 2025. Accessed August 4, 2025. https://www.eurekalert.org/news-releases/1092644

3. About Body Mass Index (BMI). CDC. News release. May 20, 2024. Accessed August 4, 2025. https://www.cdc.gov/bmi/about/index.html

4. Body fat percentage vs. BMI - Which is important? Baylor College of Medicine. News release. January 4, 2024. Accessed August 4, 2025. https://www.bcm.edu/news/body-fat-percentage-vs-bmi-which-is-important

5. Wijayatunga, N.N., Dhurandhar, E.J. Normal weight obesity and unaddressed cardiometabolic health risk—a narrative review. Int J Obes 45, 2141–2155 (2021). https://doi.org/10.1038/s41366-021-00858-7