Gut bacteria is having a moment lately, even receiving the Very Important Story treatment recently in the New York Times. The paper of record takes a deep dive into research that increasingly suggests the microorganisms swimming around your pipes not only digest food and fight disease, they secrete mood-regulating chemicals like serotonin, dopamine, and gamma-aminobutyric acid or GABA.
https://www.fatherly.com/health-science/the-link-between-gut-bacteria-and-your-kids-behavior-just-got-stronger/
Toms Blog on Life and Livingness