Various gut microbes (such as Actinobacteria, Bacteroidetes, E. coli, Firmicutes, Proteobacteria, Tenericutes, and Verrucomicrobia) and their metabolites (such as SCFAs) can play a significant role in the pathogenesis of AD via modulation of various pathophysiological processes involved in AD pathogenesis, such as neuroinflammation and other inflammatory processes, amyloid deposition, and BDNF and NMDA signaling [11,66]. This evidence concerns the gene BDNF and Alzheimer disease.