Body Roundness

Despite its widespread use, on an individual basis (in contrast to a population) body mass index (BMI) has several limitations related to risk prediction. For example, there is substantial variation both in body composition as well as fat tissue distribution between people with the same BMI. This limitation explains why other markers of adiposity, such as waist-to-hip ratio (WHR), have been shown to be stronger predictors of all-cause mortality. Where fat is stored is more predictive of risk than the total amount of fat.

This idea was further supported by an analysis of nearly 37,000 individuals who had received abdominal CT exams as part of a routine screening. In this study, an increase in subcutaneous fat was actually associated with a decrease in mortality risk. Visceral fat, and especially the ratio of visceral to subcutaneous fat, were independent predictors of all-cause mortality. Also, the cut-offs used to establish reference ranges for BMI may be ethnicity-specific. And so the search for easy-to-measure indicators of adiposity with more robust predictive value than BMI has been ongoing. 

In a nationally representative (NHANES) cohort study published in JAMA Network Open, data from roughly 33,000 U.S. adults was used to evaluate the ability of a newer metric, termed the body roundness index or BRI, to predict overall mortality. Body roundness uses waist circumference to better approximate visceral fat and total body fat percentages. A U-shaped curve related to all-cause mortality risk was observed; a low BRI (less than 3.4) was linked to a 25% increase in risk, while an elevated BRI (6.9 or higher) was associated with a 49% increase in risk. This analysis of a large U.S. cohort provides compelling evidence that BRI may be a strong candidate as a marker for risk, potentially superior to BMI.