Sleep also improves without sugar. That may be the cause also.
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.
Alternatively maybe I was already moving past the hump and would have felt better regardless but after antibiotics I’m not sure how I’d get back to a good baseline easier than yogurt or sauerkraut.
https://badgut.org/information-centre/a-z-digestive-topics/p...
Still, I think it's worth using probiotics, as there don't seem to be any negative effects.