Beyond BMI: Associations of Body-Shape Indices with CBC-Derived Systemic Inflammatory Indices in Adults with Metabolic Syndrome: A Cross-Sectional Study

Background/Objectives: Metabolic syndrome (MetS) is characterized by central adiposity, metabolic dysregulation, and low-grade inflammation, but body mass index (BMI) may not fully capture body-shape variation in established MetS. We investigated whether body-shape indices were associated with complete blood count (CBC)–derived systemic inflammatory indices after accounting for BMI. Methods: In this cross-sectional study with prospective data collection, 331 adults with MetS were evaluated. Weight-adjusted waist index (WWI) was the primary anthropometric variable and systemic inflammation response index (SIRI) the primary inflammatory variable. Body roundness index (BRI), a body shape index (ABSI), conicity index, waist-to-height ratio (WHtR), and waist-to-hip ratio (WHR) were assessed as secondary anthropometric measures, together with the systemic immune-inflammation index (SII), neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR), and lymphocyte-to-monocyte ratio (LMR). Multivariable linear regression models were adjusted for age, sex, current smoking, and BMI. Results: WWI was not significantly associated with log-SIRI after adjustment for age, sex, current smoking, and BMI (standardized β = 0.067, 95% CI −0.052 to 0.185; p = 0.268). Adding WWI increased R2 from 0.091 to 0.094 (ΔR2 = 0.0034; partial R2 = 0.0038). None of the secondary anthropometric–inflammatory associations was statistically significant after false discovery rate (FDR) correction. Restricted cubic spline analysis showed no evidence of a nonlinear WWI–SIRI association (P-nonlinear = 0.582). Additional covariate analyses in which C-reactive protein, diabetes, estimated glomerular filtration rate, coronary artery disease and heart failure were added separately did not materially alter the WWI estimate. Conclusions: In adults with established MetS, we did not detect significant associations between WWI or other body-shape indices and CBC-derived systemic inflammatory indices after adjustment for BMI. These findings do not exclude smaller associations that may not have been detectable in this cohort.