Plant-based diets especially healthy ones are negatively associated with depression: a cross-sectional study

Diet was a potentially modifiable factor in the prevention of depression. We aimed to investigate associations of an overall plant-based diet index (PDI), a healthful PDI (hPDI), and an unhealthful PDI (uPDI) with the prevalence of depression. We hypothesized that plant-based diets especially the hPDI may be associated with lower depression, whereas uPDI would increase the depression.

This is a cross-sectional study using data from the US National Health and Nutrition Examination Survey 2005-2018. Diet was assessed by 24-hour recalls. Depression was measured using the Patient Health Questionnaire-9 (PHQ-9). Odds ratios (ORs) and percentage changes (%) were calculated by logistic regression and linear regression, respectively.

Among the 31,622 participants aged 20 years or older, the age-standardized prevalence of major depression (PHQ-9 score ≥ 10) was 8.8% (n = 2,744). The overall PDI was not associated with odds of depression (OR comparing extreme quintiles 0.84, 95% confidence interval [CI]: 0.66-1.07; p_trend=0.168), whereas it was associated with lower PHQ-9 scores in multiple linear regression (β=-0.07, 95%CI: -0.13, -0.02, p_trend=0.045). Participants with higher hPDI scores had lower odds of depression (OR = 0.69, 95%CI: 0.55, 0.87, p_trend=0.007) and lower PHQ-9 scores (β=-0.07, 95%CI: -0.14, 0.00, p_trend=0.013). Conversely, higher uPDI scores were positively associated with prevalence of depression (OR = 1.78, 95%CI: 1.44-2.20, p_trend<0.001) and PHQ-9 scores (β = 0.19, 95%CI: 0.14, 0.24, p_trend<0.001).

Plant-based diets, especially when they are enriched with healthier plant foods, may be beneficial for primary prevention of depression. However, plant-based diets that emphasize less healthy plant foods are associated with higher depression levels among US adults.