There seems to be quite a lot of research in this area.<p>Another recent article, titled "What if Your Mood Depends on the Bacteria in Your Gut?":<p><a href="https://lab.cccb.org/en/what-if-your-mood-depends-on-the-bacteria-in-your-gut/" rel="nofollow">https://lab.cccb.org/en/what-if-your-mood-depends-on-the-bac...</a><p>Excerpt:<p>"The first clue to the close relationship between mind and gut came half a century ago, when experiments on mice showed that any kind of stress, from hunger to sleep, loud noises or separating pups from their mothers, altered the composition of the animals’ gut microbiota, which was linked to an increased risk of health problems. Intestinal bacteria are able to influence levels of serotonin, one of the many biochemical messengers that regulate our mood and behaviour; they promote the metabolism of dopamine, the neurotransmitter associated with joy, learning and reward; and they are involved in the release of GABA, an essential molecule in modulating behaviour."<p>The influence seems to go both says – psychological stress degrades the microbiota, and the microbiota influence psychological well-being: "studies have found that by transferring bacteria from children with autism spectrum disorder to healthy mice, the animals developed symptoms similar to those of the children, such as social aversion."