Mental health disorders, particularly depression and anxiety, pose a significant global health burden. They are leading causes of disability and contribute to increased risks of cardiovascular disease, frailty, and mortality. The COVID-19 pandemic further exacerbated these issues. Nutritional medicine is increasingly recognized as a potential strategy for preventing and treating mental health disorders. Dietary patterns, rather than individual nutrients, offer a more comprehensive approach to understanding diet's impact on mental health. Previous research has examined the associations between various dietary patterns (e.g., Mediterranean, DASH, plant-based) and mental health outcomes. However, the EAT-Lancet reference diet, designed to promote both human and planetary health, has not been extensively studied in this context. This study aimed to investigate the prospective associations between adherence to the EAT-Lancet diet and the incidence of depression, anxiety, and their co-occurrence in a large cohort of UK adults. The EAT-Lancet diet emphasizes plant-based foods, moderate amounts of seafood and poultry, and limits red meat, added sugar, and saturated fat. Understanding this association is crucial for developing effective preventative strategies.

Existing literature shows mixed results regarding the relationship between dietary patterns and mental health. A meta-analysis demonstrated that adherence to high-quality diets was associated with reduced depression risk. Studies on plant-based diets showed that a diet rich in healthy plant foods was associated with lower depression risk, while a diet high in less healthy plant foods was linked to increased risk. Research on the Mediterranean diet and DASH diet showed mixed results regarding depression risk, with inconsistencies likely due to variations in scoring systems. The EAT-Lancet diet, with its emphasis on sustainability and human health, presents a unique opportunity to further investigate these associations, given its comprehensive approach to food systems and health outcomes. This is particularly important given the lack of prior research specifically examining the EAT-Lancet diet and mental health.

This prospective cohort study utilized data from the UK Biobank, including 180,446 participants who completed at least one 24-hour dietary recall questionnaire. Participants were excluded if they withdrew from the study, had pre-existing depression or anxiety, used relevant medications at baseline, or had abnormal energy intake. Three different EAT-Lancet diet indexes (Knuppel, Stubbendorff, and Kesse-Guyot) were used to assess adherence to the diet. Incident cases of depression and anxiety were identified using self-reported medical conditions, primary care, hospital data, and death registry records. Cox proportional hazards models were employed to analyze the associations between the EAT-Lancet indexes and the incidence of depression, anxiety, and their co-occurrence. Models were adjusted for various covariates, including age, sex, socioeconomic status, lifestyle factors, and health conditions. Restricted cubic splines were used to examine dose-response relationships. Net reclassification improvement (NRI) was calculated to compare the predictive performance of the EAT-Lancet indexes with other established diet scores. Sensitivity analyses were conducted to assess the robustness of the findings, including excluding participants with limited dietary recall data, using different follow-up timepoints, excluding early-onset cases, and exploring individual food components and mediation effects.

Higher adherence to the EAT-Lancet diet was significantly associated with lower risks of incident depression, anxiety, and their co-occurrence. This association was consistent across all three EAT-Lancet indexes used in the study. Specifically: * **Knuppel EAT-Lancet Index:** The highest adherence group showed a lower risk of depression (HR: 0.806, 95% CI: 0.730–0.890), anxiety (HR: 0.818, 0.751–0.892), and co-occurrence (HR: 0.756, 95% CI: 0.624–0.914) compared to the lowest adherence group. Each additional point on the index was associated with a decreased risk of these outcomes. * **Stubbendorff EAT-Lancet Index:** The highest adherence group exhibited lower risks of depression (HR: 0.711, 95% CI: 0.627–0.806) and anxiety (HR: 0.765, 95% CI: 0.687–0.852). Similar trends were observed for co-occurrence. * **Kesse-Guyot EAT-Lancet Index:** The highest quintile showed lower risks of depression (HR: 0.844, 95% CI: 0.768–0.928), anxiety (HR: 0.825, 95% CI: 0.759–0.896), and co-occurrence (HR: 0.818, 95% CI: 0.682–0.981) compared to the lowest quintile. The predictive performance of the EAT-Lancet indexes was comparable to or slightly better than other established diet scores (Mediterranean, DASH, plant-based). Sensitivity analyses confirmed the robustness of these findings. Adherence to vegetable and fruit recommendations was strongly associated with lower risks of these mental health outcomes. Mediation analyses indicated that BMI played a role in mediating the association between the EAT-Lancet diet and depression/anxiety, while the effects of other factors (cardiovascular disease, type 2 diabetes, and hypertension) were weaker or insignificant. Interactions were found between the EAT-Lancet index and deprivation; the associations were stronger among more deprived individuals.

This study provides strong evidence supporting an inverse association between adherence to the EAT-Lancet diet and the risk of depression, anxiety, and their co-occurrence. This association is consistent across different quantification methods of the EAT-Lancet diet, suggesting robustness. The findings highlight the potential of the EAT-Lancet diet as a modifiable dietary factor for primary prevention of these mental health conditions, particularly among deprived populations. The mechanisms may be related to the anti-inflammatory effects of the plant-based components and the impact of diet on the gut microbiome. The study extends previous research by focusing on the comprehensive and sustainable EAT-Lancet dietary pattern and showing its potential benefits for mental health, in addition to its known benefits for physical health and environmental sustainability. Further research is needed to explore the underlying mechanisms in greater detail and to replicate these findings in diverse populations.

This large-scale prospective study demonstrates a significant association between higher adherence to the EAT-Lancet diet and a reduced risk of depression, anxiety, and their co-occurrence. The consistency of these findings across different EAT-Lancet indexes strengthens the evidence. Promoting this diet could have important public health implications for mental health prevention. Future research should focus on investigating underlying mechanisms, exploring potential interactions with other lifestyle factors, and replicating these findings in diverse populations and settings.

The study's limitations include the potential for underdiagnosis of depression and anxiety, the exclusion of participants with incomplete dietary recall data, the use of self-reported data, and the potential for reverse causality. The predominantly white UK Biobank sample might limit the generalizability of the findings to other populations. While adjustments were made for potential confounders, residual confounding remains possible. The analysis of the Stubbendorff score may be affected by the incomplete assessment of certain dietary components in the dataset.