Making a tangential comment here. People often say to trust one's gut when making a decision. This is good but overused and oversimplified advice. I myself told my kids in this post https://medium.com/illuminations-mirror/life-lessons-and-parents-roles-an-actual-email-to-my-15-year-old-son-and-17-year-old-daughter-48c8ef4f4ccf to trust their guts but modified that thought with "There is a difference between doubts in your head and feelings in your gut. There is a difference between being nervous in your gut and something really not feeling right in your gut." It's also oversimplified advice because as you point out the microbiome can produce it's own neurotransmitters. Moreover, fear makes our guts queasy. When I wrote my advice to my kids I was thinking of a friend who lives in fear/never risk taking. I was not thinking of fear from trauma, which Heather Woods wrote about here as why rather than trusting her gut she chooses to by guided by her values. https://medium.com/@heathercwoods/you-dont-always-have-to-trust-your-gut-if-you-re-habituated-to-being-anxious-fearful-78c2b6acf481