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.