Diet and UC symptoms are different for everybody. I would try keeping a food diary for a while and see if certain foods make a difference. I kept one for a month when my current flare started, and diet does not make much of a difference for me.
Personally, I stay away from spicy and fried foods. I don't eat nuts and limit my corn consumption. I don't drink soda or milk, but I can handle cheese. I sometimes peel my fruits and veggies. These are just precautions. Overall, I just try to eat healthy. For me, if I'm going to be in a flare, then I will be in a flare no matter what I eat or don't eat.
Also, it is better to eat multiple smaller meals rather than a few big meals--it is easier for the digestive system to break down smaller meals.
Female, Age 19, Dx w/ UC August 2007
9 Asacol, Rowasa, 1000 mg Canasa, Proctofoam, Rifaximin 2/day
Digestive Advantage (Crohn's & Colitis), 1 Florastor, 50 mg 6MP,1 Primadophilus reuteri, 1 DanActive, Remicade (2nd infusion 06/26/08), 2.4 g Lialda