- Clinical Technology
- Adult Immunization
- Hepatology
- Pediatric Immunization
- Screening
- Psychiatry
- Allergy
- Women's Health
- Cardiology
- Pediatrics
- Dermatology
- Endocrinology
- Pain Management
- Gastroenterology
- Infectious Disease
- Obesity Medicine
- Rheumatology
- Nephrology
- Neurology
- Pulmonology
Body Fat Percentage Outperforms BMI in Predicting Mortality Risk in Young Adults: New Findings
Body fat percentage and waist circumference were both significantly associated with 15-year all-cause mortality while BMI had no significant association.
The long-standing reliance on body mass index (BMI) as a measure of health risk may be challenged by a new study that found body fat percentage (BF%) is a significantly stronger predictor of all-cause and heart disease mortality in young adults. In a nationally representative cohort of more than 4,200 US adults aged 20 to 49 years (NHANES, 1999–2004), BF% was significantly associated with a 78% greater risk of 15-year, all-cause mortality (aHR 1.78; 95% CI, 1.28–2.47; P < .001) while BMI showed no significant association after adjustment.
Study authors observed similar patterns for heart disease mortality, where BF% was associated with a more than 3-fold increased risk (aHR, 3.62; 95% CI, 1.55–8.45; P = .003), again outperforming BMI. Participants were followed for 15 years.
BMI is the most commonly used measure of body composition in primary care because it is easily calculated. However, it remains an indirect estimate of adiposity based on height and weight, Arch Mainous, III, PhD, professor and vice chair of research, department of community health and family medicine at the University of Florida, in Gainesville, wrote in the Annals of Family Medicine.
“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,” coauthor Frank A. Orlando, MD, from the University of Florida, said in a statement. “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.”
The authors stress the limitations to using BMI, noting the measure can "misclassify individuals with a muscular physique as overweight or obese, and certain individuals with a normal BMI and elevated BF% (ie, normal weight obesity) may be unaware of their significantly increased risk of metabolic syndrome, type 2 diabetes, and [cardiovascular disease]," Mainous et al wrote. Moreover, BMI fails to account for differences in muscle mass, sex, and fat distribution, which can result in inaccurate and misleading risk stratification.2
Using bioelectrical impedance analysis (BIA), a non-invasive, low-cost method to measure BF%, Mainous et al compared the measure's ability to predict long-term mortality with that of BMI and waist circumference (WC).
FINDINGS
Investigators used accepted sex-specific thresholds for unhealthy BF% (27% or greater for men and 44% or greater for women), and found that BF% had a much stronger association with 15-year mortality than BMI. WC also predicted mortality risk (aHR for all-cause mortality, 1.59; 95% CI, 1.12–2.26; P =.009), but its utility in clinical practice may be limited by challenges in standardizing measurement techniques.
Importantly, the overlap in classifying individuals as healthy or unhealthy varied substantially between BMI and BF%. Mainous and colleagues reported that only 60% of the sample received concordant classifications between BMI and BF%, suggesting that reliance on BMI alone could lead to misclassification of risk in a large proportion of adults. In contrast, BF% and WC classifications aligned more closely with one another, according to the findings.
Kaplan-Meier curves further illustrated that BF% and WC were significantly associated with decreased survival over the 15-year follow-up period, while BMI had weaker predictive value. The “obesity paradox”—in which overweight individuals have lower mortality risk—did not appear in BF% or WC models, underscoring the potential of these measures to more accurately capture adiposity-related risk, investigators said.
Among the study's limitations the authors acknowledge the absence of standardized BF% thresholds comparable to those established for BMI, reliance on historic BIA data from the early 2000s, and the exclusive focus on mortality without assessing non-fatal outcomes such as myocardial infarction or newly diagnosed cancer.
"This study provided a real-life comparison of downstream risk prediction of the currently industry standard for body composition...vs other available measures," Mainous and colleagues wrote. To the argument that measures other than BMI are not viable in the standard clinical setting, they note that as BIA technology becomes faster, cheaper, and more accessible, BF% may emerge as a preferred clinical tool for assessing obesity-related risk in young adults. They do suggest that additional prospective research is needed to validate BF% thresholds and assess their relationship with both morbidity and mortality across diverse populations.
"Once these standards are validated, it is likely that measuring BF% with BIA will become standard of care. These data will drive better discussions in the doctor’s office as well as public health initiatives with the goal of improving the health of all," they concluded.
