 [ Symptoms ] what should i eat during a flare up of ulcerative colitis symptoms [ Disease ] during a flare up the large intestines become inflamed causing diarrhea and discomfort many experts recommend going on a non residue diet    one that eliminates foods that are difficult to digest or that contain indigestible fiber that means avoiding fruits and vegetables nuts and seeds and whole grains some doctors recommend a liquid diet during severe flare ups with no food passing through the large intestines the bowels have time to heal a low residue diet is also recommended for people who have developed a narrowing of the lower small intestine called the ileum keep in mind that no two people respond the same way some patients do well on a low fiber low residue diet but every patient is different  says david t rubin md co director of the inflammatory bowel disease center at the university of chicago