Kazemi A, et al. - Researchers pursued a comparison of the effect of supplementation with the probiotic and prebiotic on the Beck Depression Inventory (BDI) score as a primary outcome as well as the kynurenine/tryptophan ratio and tryptophan/branch chain amino acids (BCAAs) ratio as secondary outcomes in patients with major depressive disorder (MDD). An improvement was achieved in the BDI score due to 8 weeks of probiotic supplements in individuals with MDD compared with placebo. On the other hand, findings did not reveal any prominent effect of prebiotic supplementation. Furthermore, tryptophan/isoleucine ratio increased significantly in the probiotic group when compared to the placebo group.