Plant-Based Diets and Depression: Epidemiological Evidence, Biological Mechanisms, and Implications for Prevention

Hanni Li¹Yao Gao²Ze-Kun Li³Jiaojiao Qiao³Yi-Xuan Peng³Sha Liu^2*Xin Yan^1*

• ¹First Hospital of Shanxi Medical University, Taiyuan, China
• ²Department of Psychiatry, First Hospital of Shanxi Medical University, Taiyuan, China
• ³Shanxi Medical University, Taiyuan, China

Depression is a leading global mental health burden, and diet has emerged as a modifiable risk factor. This narrative review summarizes evidence about the association between plant-based dietary patterns and depression. It focuses particularly on diet quality and potential mechanisms. We examined plant-based diets—defined by the Plant-Based Diet Index (PDI), healthy PDI (hPDI), and unhealthy PDI (uPDI)—and plant-forward dietary patterns such as the Mediterranean, DASH, and MIND diets in relation to depressive symptoms or diagnosed depression. In diverse populations, greater adherence to healthful plant-based dietary patterns that emphasize minimally processed plant foods typically correlates with reduced depressive symptoms, better mental health, and improved quality of life. Conversely, diets that are high in ultra-processed, energy-dense plant foods are associated with a higher risk of depression. Proposed mechanisms include reduced systemic inflammation, beneficial modulation of the gut microbiota and the microbiota–gut–brain axis, and improved intake of key nutrients and phytochemicals involved in monoamine neurotransmission, neurotrophic signaling, and oxidative stress defense. In general, the influence of plant-based diets on depression seems to be more closely related to diet quality and nutrient adequacy rather than merely the elimination of animal foods.