The Hidden Health Penalty for the Poor: How Food Delivery Consumption Exacerbates Socio-Metabolic Vulnerability to Drive Obesity in Urban China

Background: Health inequality represents a critical public health challenge amidst China's rapid urbanization. The underlying mechanisms through which prevalent lifestyle changes, such as the surge in online food delivery consumption, contribute to disparate health outcomes across socioeconomic strata remain poorly understood. This study aimed to introduce and validate a novel construct, "Socio-Metabolic Vulnerability (SMV)," to elucidate the pathway linking food delivery habits to obesity and to examine the moderating role of socioeconomic status (SES) in this process. Methods: We conducted a large-scale, cross-sectional study involving 20,135 adults in Wuxi, a representative metropolis in China, using a multi-stage stratified random sampling method. Data on food delivery habits and sociodemographics were collected via questionnaires, while obesity and related metabolic indicators were assessed through anthropometric measurements and biochemical assays. The SMV index was constructed using exploratory factor analysis (EFA) on eight pre-selected social and metabolic variables. A moderated mediation model was employed to test the primary hypotheses. Results: Baseline characteristics revealed a significant social gradient, with individuals of low SES exhibiting higher food delivery frequency, elevated SMV index scores, and greater obesity prevalence (all p < .001). EFA confirmed a robust two-factor structure ("Social" and "Metabolic") for the SMV index, explaining 68.4% of the total variance. Path analysis established that SMV significantly mediated the association between food delivery frequency and BMI (standardized indirect effect β = 0.35). Critically, this mediation pathway was significantly moderated by SES (index of moderated mediation = -0.10, 95% CI: -0.14, -0.07). The conditional indirect effect was over three times stronger in the low-SES group (B = 0.31, 95% CI: 0.26, 0.37) compared to the high-SES group (B = 0.10, 95% CI: 0.07, 0.14). This mechanism was more predictive of severe combined obesity (OR = 1.28 for low-SES group) and was particularly pronounced among men and younger adults. A non-linear, accelerating dose-response relationship was observed. Conclusion: Food delivery consumption appears to drive obesity by exacerbating an individual's underlying Socio-Metabolic Vulnerability. This detrimental health effect is disproportionately amplified among individuals of lower socioeconomic status, uncovering a novel mechanism of health inequality in the context of modern urban lifestyles. Public health interventions must transcend individual-level behavioral counseling to address the structural socioeconomic environments that heighten this vulnerability.