BACKGROUND - The association between depression and the metabolic syndrome remains poorly understood. Diet and physical activity may partly explain this association. METHODS - Baseline data on 64,861 subjects from the French population-based Constances cohort was analyzed. Depressive symptoms were determined with the Center of Epidemiologic Studies Depression (CES-D) scale. A CES-D score ≥ 19 combined with self-reported limitations related to depressive symptoms was used to define depression. The metabolic syndrome was defined according to the International Diabetes Federation criteria. Dietary patterns were determined with a food frequency questionnaire and a principal component analysis. Physical activity was measured with 3 questions resulting in a composite 6-point scale. Associations between depression and the metabolic syndrome were estimated through logistic regression and path analysis. RESULTS - The odds-ratios (95% confidence interval) for the association between depression and the metabolic syndrome, adjusting for age, sex, education and income, was 1.75 (1.57-1.96). The path analysis showed that 23% of this association was explained by diet and physical activity, 67% being attributed to physical activity. LIMITATIONS - The cross-sectional nature of the analyses warrants the results to be confirmed by longitudinal analyses. CONCLUSION - Diet and physical activity might partially explain the association between depressive symptoms and metabolic syndrome but other factors (e.g. inflammatory factors) are involved.