I have ulcerative colitis and have successfully maintained remission for years with a combination of diet, exercise and natural supplements - particularly probiotics. (I do remain on a low maintenance dose of sulfasalzine/azulfadine, at my doctor's request and because it's relatively safe compared to the high powered steroids and auto-immune drugs.)
I use different variations of diet including the Specific Carbohydrate Diet and Autoimmune Paleo, but the common thread is grain-free and dairy-free. I believe you DO have to tailor the diet to your specific needs. I do well on the SCD, but I can't tolerate the SCD approved yogurt. Keep a food journal to track what you're eating and your resulting symptoms and modify from there. I'm currently experimenting with intermittent fasting - daily fast from 8 p.m. to noon the next day - and am having good results.
BTW, no GI doc has ever expressed any interest in learning what's allowed me to stay in remission for so long.