I suffered with Ulcerative Colitis after a lifetime of having a cast iron gut. I changed two things and it went into remission and has not returned.
1. I stopped drinking lightly filtered tap water and switched to heavily filtered water for everything I drink with water in it. I believe I personally developed a sensitivity to the chlorine or whatever the water treatment plant uses and it messed up my gut microbiome.
2. I all but gave up some of my favorite dairy products like ice cream and yogurt. One would think yogurt would be good with all the probiotics but not for me. I still eat cheese and once in a while I will have some soft serve ice cream at a restaurant.
Now this is what worked for me but I doubt it will work for everyone. Neither is an expensive thing to do so may be worth a try. It never hurts to have a good water filtering product as a backup prepper item too.
I’ve had UC for 29 years now. We have had filtered water for the last 7 years and I can’t say that it’s hurt or helped. I do eat some fiber-you’re “damned if you do and damned if you don’t”.
On the one hand, it helps keep things moving and lowers the risk (supposedly) of developing colon cancer, and on the other hand it can aggravate colitis.
I don’t consume a diet heavy in fiber, but I do eat some, unless the disease is really active.