Background/Objectives: The Planetary Health Diet has been associated with lower risk of multiple chronic diseases, nonetheless, its relationship with depression remains unravelled.

Methods: This prospective study used data collected by the SUN project, which is an ongoing cohort that encompass Spanish college graduates. Dietary exposure was assessed at baseline through a validated food frequency questionnaire and updated after 10 years of follow-up. Adherence to the Planetary Health Diet was measured using two different indices (Eat-Lancet Index and Planetary Health Diet Index). A previously validated self-reported medical diagnosis of depression in follow-up questionnaires was considered as the outcome. Cox regression models were performed to obtain hazard ratios using the tertile of lowest adherence as reference.

Results: In a sample of 16,231 individuals, 997 incident cases were identified. No significant associations were obtained in the fully adjusted model using the Eat-Lancet Index comparing extreme tertiles of adherence (HR 0.96, 95%CI: 0.82 - 1.14, p for trend = 0.641) or the Planetary Health Diet Index (HR 0.87, 95%CI: 0.74 - 1.02, p for trend = 0.096). Updated and cumulative average models were performed using both indices and they yielded comparable results. Sensitivity analyses confirmed the robustness of our findings.

Conclusions/Recommendations: No significant association between the Planetary Health Diet adherence and the risk of depression was found in this Mediterranean cohort. Further research is needed to reach a consensus on its operational definition and to clarify its potential relationship with depression.

Funding: PI23/01332, Instituto de Salud Carlos III-Fondos FEDER.