Predicting the metabolically obese normal weight phenotype: sex-specific diagnostic accuracy of traditional and novel anthropometric indices

Objectives The aim of this study was to compare the sex-specific diagnostic performance of traditional anthropometric indices, including Body Mass Index (BMI), Waist Circumference (WC), Waist–Hip Ratio (WHR), and Waist-to-Height Ratio (WHtR), with novel indices such as A Body Shape Index (ABSI), Body Roundness Index (BRI), Abdominal Volume Index (AVI), Weight-Adjusted Waist Index (WWI), Body Adiposity Index (BAI), Conicity Index (CI), and Waist–Hip–Height Ratio (WHHR) in predicting the Metabolically Obese Normal Weight (MONW) phenotype in adults.Methods This diagnostic accuracy study involved 504 adults aged 19–64 years who met specific inclusion and exclusion criteria. Metabolic abnormalities were evaluated according to NCEP-ATP III criteria to identify the MONW phenotype. The ability of the anthropometric indices to discriminate MONW individuals was assessed using Receiver Operating Characteristic (ROC) curves, with optimal cutoff points determined by the Youden index. Results: Results indicated that 18.10% of adults had the MONW phenotype, and the proportion of men with MONW was higher than that of women (p < 0.05). ROC analysis revealed that among women, WHtR (AUC: 0.715, 95% CI: 0.598–0.832) among traditional indices and BRI (AUC: 0.712, 95% CI: 0.594–0.830) among novel indices showed fair predictive ability, while other indices demonstrated weak or no predictive power. In men, all indices exhibited poor or no performance in predicting the MONW phenotype.Conclusion These findings suggest that anthropometric indices alone have limited capacity to identify MONW, especially in men, emphasizing the importance of comprehensive, multi-parameter assessments to detect high-risk normal-weight adults.