Predictive Effects of Waist Circumference-Related Anthropometric Measures on Body Mass Index in South African...

Background: Body mass index (BMI) is commonly used to assess obesity but does not differentiate between fat and lean mass, limiting its effectiveness to assess cardiometabolic risk. Measurements of central adiposity, such as waist circumference (WC), waist-hip ratio (WHR) and waist-to-height ratio (WHtR), are better predictors of metabolic dysfunction, especially with respect to visceral fat. Aim: To examine BMI trends and assess the association between BMI and waist-related anthropometric indicators WC, WHR, and WHtR, among university students in South Africa. Methods: A cross-sectional study involving 842 university students was conducted. Anthropometric measurements were taken according to ISAK standards. Quantile regression models supplemented by ROC curves were used to assess the predictive effects of WC, WHR, and WHtR on BMI across its distribution. Results: A total of 842 participants (63.8% female) were included, with a mean age of 21.8 ± 4.0 years. Significant differences were observed across BMI categories for all demographic and anthropometric characteristics (p < 0.001). Quantile regression analyses showed that WHtR and WC were strong and consistent predictors of BMI in all quantiles, with effect sizes increasing at higher levels of BMI. The WHR showed weaker associations overall, but these became significant in the upper BMI quantiles. Collectively, waist-related indicators, particularly WHtR and WC, exhibited robust predictive values for elevated BMI. Conclusions: Waist-related indicators, especially WHtR and WC are robust predictors of elevated BMI among university students, particularly in higher BMI ranges. These findings highlighted the value of incorporating central adiposity measures alongside BMI for more accurate health risk assessments in young adult populations.