The gut brain connection, more explicitly the microbiota, is directly tied into anxiety and depression. This is a major reason broad spectrum antibiotics should only be used when absolutely necessary plus a well round diet is vital!
More mind blowing is the recent research showing Fecal Transplants helping with Autism. It’s been demonstrated microbiota dysbiosis when young is associated with developing Autism, and Fecal Transplants allow for a healthly microbiota to replace the one in disarray.
Here’s a research paper digging into the depression and anxiety apects if you’re interested: Gut Microbiota in Anxiety and Depression - Unveiling the Relationships and Management Options www.ncbi.nlm.nih.gov/pmc/articles/PMC10146621/