Researchers have found gut bacteria to be such an influencing factor on human health that they now refer to the gut microbiome as the “second brain.” Gut bacteria produce neurochemicals that circulate through our bloodstream.  Microbes both synthesize and respond to neurochemicals. And this affects both the immune system and the brain, including psychology. Dr. Reid adds that many of the probiotic strains that we eat in traditionally fermented foods, such as sauerkraut, kefir, kimchee, and yogurt, are producing neurochemicals.