NFE2L2 and major depressive disorder: Although the mechanistic evidence on how SCFAs modulate neurological disorders is not well-documented, several signaling pathways including the peroxisome proliferator-activated receptor gamma (PPARγ) pathway and the Nuclear factor erythroid 2-related factor 2 (Nrf2) redox pathway might be involved, since the activation of both signaling pathways are related to the alleviation of depression and stress (Yao et al., 2016; Gold, 2021).