Advances in lactic acid bacteria and its fermented milk mitigate depression in mice via the microbiota–gut–brain axis

Depression is a highly prevalent and complex mental disorder with significant therapeutic limitations. This review comprehensively examines how lactic acid bacteria (LAB) and fermented dairy products alleviate depressive symptoms via the microbiota-gut-brain axis (GBA). It further summarizes recent advances in probiotic delivery technologies and outlines future directions for developing effective LAB-based interventions. Acting as psychobiotics, LAB can mitigate depressive-like behaviors in rodent models. Evidence indicates this effect occurs through multiple pathways, including the modulation of tryptophan metabolism, the suppression of neuroinflammation, and the engagement of vagus-nerve-mediated signaling. Specific strains such as Lactiplantibacillus plantarum and Lacticaseibacillus paracasei have demonstrated pronounced antidepressant effects. This is reflected by elevated levels of serotonin (5‑HT) and brain‑derived neurotrophic factor (BDNF). These effects are coupled with reductions in inflammatory markers. The synergistic effects of LAB within fermented‑milk matrices further enhance functionality through the generation of bioactive metabolites such as γ‑aminobutyric acid (GABA), short‑chain fatty acids (SCFAs), and peptides. Translating these findings into practice requires overcoming crucial delivery challenges. Advances in microencapsulation and targeted delivery systems are pivotal for protecting LAB viability and ensuring effective colon release. Future integration of AI for modeling gut-flora homeostasis and personalizing delivery platforms holds great promise. In conclusion, this review consolidates the potential of LAB and fermented dairy products as dietary strategies against depression, synthesizes underlying mechanisms, and highlights delivery technologies. Together, these insights provide a foundation for developing next-generation functional foods and precision-nutrition interventions targeting the GBA.