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Abstract Purpose Plant-based diets (PBDs) have been linked with favourable cardiometabolic health outcomes. However, there has been limited investigation of PBD indices (PDIs) and mental health outcomes. Addressing this gap, we examined an overall PDI (oPDI), healthy PDI (hPDI) and unhealthy PDI (uPDI) associations with depressive symptoms, anxiety and well-being. Methods This cross-sectional study includes 1,949 middle- to older-aged men and women from the Mitchelstown Cohort. PDIs were calculated from validated food frequency questionnaires. Depressive symptoms, anxiety and well-being were assessed using the 20-item Center for Epidemiologic Studies Depression (CES-D) Scale, the anxiety sub-scale of the Hospital Anxiety and Depression Scale and the World Health Organization-Five Well-Being Index. Regression analyses investigated PDI relationships with mental health scores, adjusted for potential confounders. Results In age and sex-adjusted models, the oPDI and hPDI were negatively associated with depressive symptoms (β = −0.095, 95% CI: −0.154, −0.036; p = 0.002 and β = −0.086, 95% CI: −0.136, −0.035; p = 0.001, for oPDI and hPDI scores respectively), and positively associated with greater well-being (β = 0.045, 95% CI: 0.006, 0.084; p = 0.025 and β = 0.037, 95% CI: 0.003, 0.071; p = 0.032, for oPDI and hPDI scores respectively). Additionally, the oPDI was inversely associated with anxiety (β = −0.027, 95% CI: −0.053, −0.002; p = 0.038). Higher oPDI and hPDI score associations with fewer depressive symptoms, and oPDI score associations with anxiety, persisted upon full adjustment, with PDI quartiles demonstrating significant dose-response relationships with CES-D scores ( p trend < 0.05). Conclusions Greater adherence to an overall PBD, and more healthful PBD, is associated with fewer depressive symptoms and greater well-being among middle- to older-aged adults. Future longitudinal studies which explore causal relationships between PDIs and psychological outcomes are warranted.
Millar et al. (Tue,) studied this question.