Updated: Nov 12
Numerous studies indicate that, compared to body mass index (BMI) or total body fat, waist-to-hip and waist-to-height ratios show stronger associations with risk for cardiometabolic disease and all-cause mortality. A paper published recently in JAMA Network Open Diabetes and Endocrinology showed that compared to BMI and fat mass index (FMI), the waist-to-hip ratio (WHR) showed the strongest and most consistent relationship with all-cause mortality. The BMI is increasingly recognized as a flawed metric. It’s useful on a population level, but it falls short when assessing individuals. Because it takes into account just two things – height and weight – with no accounting for body composition (fat mass versus lean mass), some individuals may be classified as “overweight” yet be in excellent health (consider a professional athlete who’s heavy relative to their height, owing to muscle), while millions of people fall into the “healthy” weight category yet carry a high body fat percentage and may already be living with, or be at increased risk for, cardiometabolic disease. In the JAMA study, data were gathered from over 380,000 participants in the UK Biobank (which includes data from 22 clinical centers across the United Kingdom). Both BMI and FMI were found to have J-shaped curves with respect to all-cause mortality, while the association between WHR-mortality did not differ across BMI quantiles. Even at a low or “healthy” BMI, increased abdominal fat appears to be detrimental for health, an association that explains the presence of cardiometabolic diseases, such as type 2 diabetes, among individuals who are not overweight or obese. The WHR is convenient to use in clinical practice because it requires no specialized equipment to measure body fat, such as a bioimpedance device. Plus, where the fat is located appears to be a stronger indicator of mortality risk compared to the total body fat mass. A shortcoming of the study is that all subjects British Caucasians, so the findings may not accurately represent other populations. Additionally, all adiposity measures were assessed at baseline, so it was not determined whether changes in adiposity over time may impact mortality.