Psychobiotic fermented foods for depression: Current evidence and future directions

Major depressive disorder (MDD) remains a leading cause of disability worldwide, constrained by incomplete response and side effects in conventional pharmacotherapy. Emerging evidence implicates the microbiota–gut–brain axis in mood regulation, positioning dietary psychobiotics as promising complementary interventions. This mini review synthesizes mechanistic pathways linking psychobiotic activity to neurobiological targets (HPA axis modulation, neurotransmitter synthesis, reduced neuroinflammation, and BDNF enhancement) and evaluates preclinical and clinical data on fermented foods in depressive disorders. Unlike isolated probiotic supplements, fermented foods provide diverse live microbial communities within protective matrices rich in prebiotics and bioactive metabolites, potentially enhancing viability, adherence, and clinical effect sizes. Novelty: This review prioritizes traditional fermented foods over supplements as psychobiotic delivery systems, integrating nutritional psychiatry with food science frameworks, and aligning with functional food development models, thereby offering a conceptual bridge from ancient dietary practices to evidence-based depression management.  Keywords: Depression, Psychobiotics, Fermented Foods, Microbiota–Gut–Brain Axis, Functional Foods, BDNF.