BDNF and major depressive disorder: In this study, we found that BDNF levels in the serum and brain tissues of mice with colitis were significantly increased after LSDF intervention (p < 0.05), while there was no significant difference in the BDNF levels after the HSDF intervention compared with the DSS group (p > 0.05), which suggests that the LSDF intervention is more effective in increasing BDNF levels and thus alleviating depression.