To arrive at a diagnosis of "irritable bowel", the doctor must have conducted a series of tests to rule out other diseases. If no known disease has been found, the symptoms together are called "irritable bowel syndrome".
Ulcerative colitis is inflammation of the inner lining of the colon, causing pain and often bleeding and diarrhea. There are medications used to reduce inflammation, and thereby stop the symptoms of ulcerative colitis. Good nutrition is important when fighting any disease or condition but there are some foods to avoid.