Association between plant-based diet indices and depressive symptoms among South Korean adults: a cross-sectional study using the 2014 and 2016 Korea National Health and Nutrition Examination Surveys

Objective: This study investigated the association between plant-based diet indices—overall plant-based diet index (PDI), healthful PDI (hPDI), and unhealthful PDI (uPDI)—and depressive symptoms in South Korean adults.Methods: This cross-sectional study analyzed 5,846 participants (aged 19–64 years) using data from the 2014 and 2016 South Korea National Health and Nutrition Examination Survey. Dietary intake was assessed with a semiquantitative food frequency questionnaire, from which PDIs were derived. Depressive symptoms were assessed using the Patient Health Questionnaire-9 (PHQ-9). Survey-weighted linear and logistic regression models were applied to assess associations, adjusting for sociodemographic, lifestyle, and clinical factors.Results: In fully adjusted models, higher overall PDI and hPDI were associated with lower PHQ-9 scores (β=−0.23; 95% confidence interval [CI], −0.41 to −0.04 and β=−0.16; 95% CI, −0.30 to −0.02 per 10-unit increment, respectively), whereas higher uPDI scores were associated with higher PHQ-9 scores (β=0.21; 95% CI, 0.07 to 0.35 per 10-unit increment). For clinical depressive symptoms (PHQ-9 ≥10), each 10-unit increase in overall PDI was associated with a 33% reduction in odds (odds ratio, 0.67; 95% CI, 0.50 to 0.89). Associations for hPDI and uPDI were attenuated and not statistically significant. Subgroup analyses revealed that these associations varied by sex, age, and obesity status.Conclusion: Greater adherence to healthy plant-based foods and lower intake of less healthy plant-based foods were associated with fewer depressive symptoms among South Korean adults. These findings highlight the importance of plant-based food quality, rather than quantity alone, in supporting mental health.