Food affects my UC only in a very general way.
If I go too long between meals my intestines start grumbling and swooshing, then the area below my belly button starts inflating and I am overcome with cramps and gas-type pains. - It doesn't really increase my bm's or blood or mucus, but does increase my discomfort.
Then again, if I am in good solid flare day, then eating anything at any meal will trigger diarrhea and cramps often before the meal is over.
I used to think certain foods caused my symtoms to get worse, but they were just coincidences because I would avoid them and it made no difference. These were usually food that caused my stomach (not intestines) to hurt, but I found that what bothered my stomach did not bother my UC.
I remember reading somewhere about a survival skill developed in the brains early man in which we carry around in us a certain "repugnant response" when we come across something we previously ingested just prior to getting ill. Of course it is not always the food that caused our symptoms in the first place, but often some other factor such as bacteria living in the food, yet that ancient survival part of the brain produces that twinge of nausea or repugnance when we smell or see the food again that we associate with illness so that we are often incapable of eating it happily again.