My first GI said diet doesn't have anything to do with UC. Uh.... you're telling me that what I put into my digestive tract doesn't make any different with the swelling inside my digestive tract??? So I went to another GI, who said he had heard all sorts of things about
diet, and if I wanted to try some different diets, I was more than welcome to give it a go. Basically he said his training was in medicine and that's what he was qualified to tell me (e.g. perscribe meds), but certainly there is anecdotal evidence in favor of diet modification.
I also was tested for Celiac but came back negative. Though my mother's side of the family tends to have a LOT of food issues, including Celiac and gluten intolerance. So I decided I'd go 100% gluten-free.
I tried the SCD and GAPS diet, which didn't seem to make much difference, except that cutting out grains eliminated my bloating. HOORAY!!! Like you, I did not enjoy looking pregnant all the time. I find that I can tolerate some grain/starches (all gluten-free, of course) if I eat them with digestive enzymes. Then I do not have bloating issues. I also eat very very few grains/starches, like maybe 1 serving per day.
Like so many others have already posted, I found that keeping a food journal for a couple of months was VERY helpful. It does take a while to keep track of absolutely EVERYTHING you eat, and watch for patterns, but it is very worth the effort.
I have completely eliminated sugar and gluten and anything processed that came out of a package. I spend an absurd amount of time making my own foods from scratch, but it has been worth it from a health standpoint. Going out to eat, or dining at other's houses, however, is difficult. If I'm eating out, I generally go with salad (no dressing except for olive oil) and maybe something like eggs or chicken, pretty basic. Definitely no dessert. I'm now a big fan of fermented foods, like saurkraut. Yum.
One thing you will definitely find for yourself after talking with people and reading posts here, is that everyone has different foods that affect them. The most common, though, seem to be things like wheat/gluten, grains/starches, dairy, sugar, coffee, alcohol. Good luck to you!