Prevalence and Determinants of General and Central Obesity in Central-Southern Bulgaria: Associations with Cardiometabolic Risk and Lifestyle Factors

Background: Obesity represents a major public health challenge worldwide and contributes substantially to the burden of type 2 diabetes and hypertension. While body mass index (BMI) is widely used in clinical practice, indices reflecting central adiposity may provide additional prognostic value. This study aimed to assess the prevalence of general and central obesity in an adult population across different age groups from Stara Zagora, Bulgaria, and to examine their associations with cardiometabolic outcomes and lifestyle factors. Methods: A quasi-representative cross-sectional study was conducted among 3512 adults (mean age 53.7 ± 14.9 years). Anthropometric indices, including BMI, waist circumference, waist-to-hip ratio, and waist-to-height ratio were measured. Cardiometabolic outcomes included diabetes, hypertension, and their combined presence. Multicollinearity was assessed using the Variance Inflation Factor (VIF), and the discriminatory ability of indices was evaluated using Receiver Operating Characteristic (ROC) analysis and DeLong’s test. Results: The prevalence of overweight/obesity (BMI ≥25) was 68.4%, while central obesity (WHtR ≥0.5) affected 66.9% of participants. BMI demonstrated the highest discriminatory ability in this dataset for hypertension (AUC = 0.852) and diabetes (AUC = 0.796), significantly outperforming WC and WHR (p < 0.05). However, 24.4% of individuals with normal BMI exhibited high-risk central adiposity. Significant sex-specific differences were observed: short sleep duration (<6 h) was a strong predictor of obesity in women (aOR = 2.98), whereas smoking showed stronger associations in men. Age-stratified analyses revealed that while BMI stabilizes in the oldest age group (75–89 years), WHtR continues to increase, reflecting age-related redistribution of visceral fat. A strong protective effect of physical activity was observed, supported by quasi-complete separation in active subgroups. Conclusions: General and central obesity represent a substantial health burden in this urban population. While BMI remains a robust screening tool, the integration of WHtR enhances the identification of “hidden” cardiometabolic risk particularly in older adults and individuals with normal BMI. Given the quasi-representative nature of the sample, these findings are primarily generalizable to similar urban populations and may inform targeted regional public health strategies.