I'm re-watching the Dr. Gominak video that I linked in the other thread. She's discussing the needs of the microbiome. We're living on the cutting edge of science, so we don't know so much.

Dr. Gominak says that you need to get your Vitamin D levels above 40 so that the gut bugs can live happily. You also need to supply B-50 or B-100 for 3 months, but continuing too long or too high a dose can cause problems.

She's not a microbiome specialist, but has learned a lot from her medical practice.