Probiotics For Depressive Symptoms: Gut–Brain Axis Mechanisms, Evidence, and Functional Food Translation

Abstract The prevalence of stress-induced mental health disorders, such as anxiety and major depressive disorder, is increasing globally. Growing evidence suggests that gut microbiota plays a crucial role in cognitive function and emotional regulation via the gut-brain axis. As a result, probiotics have emerged as a promising dietary intervention for mental well-being, supported by their demonstrated ability to alleviate depressive behaviors in both clinical and preclinical settings—primarily through immune modulation, metabolic regulation, and microbial metabolite production. Although numerous studies have confirmed the potential of various probiotic strains to reduce depressive symptoms, only a limited number have been approved for commercial use to date. Key challenges remain, including variable clinical efficacy, instability during production and processing, and safety considerations, which must be addressed to facilitate their integration into functional foods. This comprehensive review discusses the mechanisms by which probiotics exert antidepressant effects, with a focus on host immunity, microbial metabolites, and neuroendocrine pathways. Furthermore, we offer critical insights into the current limitations and strategic directions for the application of probiotics in functional foods aimed at supporting mental health.