In this study, the abundances of Lachnospiraceae (Lachnospiraceae_uc (p < 0.0056) and Murimonas (p < 0.0061)) were positively correlated with BDNF levels in the depression group (before flavonoid treatment), and the abundances of OCTT_g (Ruminococcaceae, p < 0.0002) were negatively correlated with serum BDNF levels. Here, BDNF is linked to major depressive disorder.