Plant-based diets and depression: epidemiological evidence, biological mechanisms, and implications for prevention

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.