Comparative Performance of Body Mass Index and Simple Anthropometric Indices for Identifying Body Fat...

Background/Objectives: Obesity is a major public health concern, and accurate diagnosis is essential for effective treatment and prevention strategies. Obesity screening utilizes anthropometric indices, among which body mass index (BMI) has been most widely used; however the comparative performance of alternative indices still needs to be evaluated. Methods: This cross-sectional study included 1042 participants. Anthropometric indices including BMI, waist circumference (WC), waist-to-height ratio (WHtR), waist-hip circumference ratio (WHR), neck circumference (NC), and hip circumference (HC) were measured among Saudi adults. Body fat percentage was measured using bioelectrical impedance analysis and used to define obesity. Correlation analysis was used to assess associations with BF%, and receiver operating characteristic curve analysis was used to compare discriminatory performance and determine optimal obesity-screening cutoffs using the Youden index. Results: The study included 1042 Saudi adults, predominantly women (61.9%), with a mean age of 31.8 ± 12 years. BMI showed the strongest overall correlation with body fat percentage (r = 0.707), followed by hip circumference and waist-to-height ratio. ROC curve analysis revealed excellent discriminatory performance for BMI in the total cohort (AUC = 0.924, 95% CI: 0.908-0.939), followed by HC (AUC = 0.887) and WHtR (AUC = 0.861); the least discriminatory performance was for WHR (AUC = 0.667). Further sex-stratified analysis showed that BMI had the strongest correlation with BF%, in both men (r = 0.837), and women (r = 0.821). On the other hand, ROC analysis showed that WHtR was the best in men (AUC = 0.932), with performance comparable to BMI, whereas BMI remained the strongest discriminator in women (AUC = 0.930). Conclusions: BMI demonstrated the highest discriminatory performance for identifying BF-defined obesity in this cohort, supporting its value as a practical and reliable screening index. Although waist circumference and waist-to-height ratio reflected differences in body fat distribution, they did not outperform BMI. These findings support the continued use of BMI as the primary obesity screening measure, while highlighting the importance of using sex-specific interpretation of complementary anthropometric indices.