Optimum Cut-Off Points of Conventional and Novel Anthropometric Indices for Obesity Screening in Young Japanese Females: A Pilot Study

Background: Conventional anthropometric indices such as body mass index (BMI), waist circumference (WC), and waist-to-height ratio (WHtR) are widely used for obesity screening; however, their accuracy may be limited in young Japanese women, who often exhibit higher percentage body fat (%BF) at lower BMI values. This pilot study examined the relationships between DXA-derived %BF and anthropometric indices and evaluated their ability to identify excess adiposity. Methods: A cross-sectional study was conducted among 78 Japanese female university students aged 18–28 years. Whole-body composition was assessed using dual-energy X-ray absorptiometry (DXA), and excess adiposity was defined as %BF ≥ 30%. Receiver operating characteristic analyses were performed to evaluate the discriminatory ability of anthropometric indices and identify exploratory optimal cut-off values. Results: Participants had a median BMI of 20.3 kg/m2 and a mean %BF of 32.3 ± 5.4%. Conventional BMI, WC, and WHtR thresholds showed very low sensitivity for detecting excess adiposity despite perfect specificity. ROC analyses identified substantially lower optimal cut-off values, yielding sensitivities of approximately 70–80%, specificities of 58–75%, and AUC values of 0.76–0.78. Among novel anthropometric indices, body roundness index (BRI) demonstrated the strongest discriminatory ability. Conclusions: Conventional anthropometric thresholds may underestimate DXA-defined excess adiposity in young Japanese female university students. This exploratory pilot study identified lower candidate cut-off values and suggested that BRI may serve as a useful adjunctive anthropometric index for identifying excess adiposity in this population. These findings should be interpreted cautiously and require validation in larger and more diverse populations before clinical application.