[cpncrunch]

Sorry for the confusion. When I mentioned coffee I was referring to IBS symptoms, not microbiome. Caffeine increases digestive secretions and causes colonic motor activity. Even decaf coffee increases secretions. For a review, see:

https://www.tandfonline.com/doi/abs/10.1080/0036552997500255...

If coffee is causing IBS symptoms (diarrhea), I would imagine that isn't good for your microbiome.

I haven't had any microbiome tests, and it's very difficult to robustly test for the effects of individual foods without doing a placebo controlled trial. However, after removing fizzy HFCS soda drinks, I seem to not have any symptoms that I would associate with an abnormal microbiome in the past year (smelly farts, followed by urgent need to poop, followed by large amount of soft poop after eating, during a period of long-term zero stress). I've made a number of other changes to my diet, such as not drinking tap water, but I suspect HFCS was the main culprit, as the scientific evidence strongly backs that up.

Stress is another main cause of IBS, due to its effects on gut motility.