Introduction: Health behaviors and environmentally relevant behaviors influence both individual well-being and planetary sustainability. Although their immediate goals differ, they may share underlying psychological mechanisms. The COM-B model provides a framework for understanding and intervening in behavior, yet its cross-domain applicability remains insufficiently tested, limiting interventions that simultaneously target health and environmental behaviors. Identifying shared mechanisms is therefore essential to design integrated strategies that achieve a "win-win" for personal health and planetary sustainability.
Methods: Using ISSP data from over 30 countries (health modules 2011 & 2021; environment module 2020), we selected four outcomes: fruit and vegetable intake and physical activity (personal health), and red meat consumption and outdoor recreation (environmental behaviors). These indicators capture typical health-promoting actions and environmental pathways: reducing red meat mitigates carbon emissions, while outdoor activities enhance nature engagement and pro-environmental awareness, enabling a test of COM-B's cross-domain generalizability. Using machine learning methods, predictors were first identified with random forests to select the 30 most important variables, followed by eight supervised models, with SHAP values aggregating predictors into COM-B dimensions. Logistic regression tested significance, and East-West subgroup analyses assessed cultural moderation.
Results: Models showed moderate predictive performance. Capability consistently emerged as the strongest predictor, followed by Motivation, with Opportunity contributing least. Eastern samples relied more on Capability for health behaviors, Western samples on Motivation. For environmental behaviors, Eastern samples showed higher contributions across all dimensions, with Capability driving meat reduction and Capability and Motivation supporting outdoor recreation; Western participants relied more on Motivation. Mann-Whitney U tests and interaction regressions confirmed cultural moderation.
Conclusion: These findings indicate that individual health and environmental behaviors share a core Capability-driven mechanism, while Motivation and Opportunity effects are domain- and culture-specific. COM-B's cross-domain applicability is empirically supported, informing integrated interventions that strengthen Capability and contextually mobilize Motivation to advance both personal and planetary health.