In ulcerative colitis, there is inflammation of the gut lining making it very sensitive in nature. Even a slight touch of food or water may exacerbate pain in the abdomen which may result in cramps or discomfort. Also, with ulcerative colitis, there is diarrhea and loose stools due to indigestion which may be past post meals. All these factors such as abdominal pain, and diarrhea cause loss of appetite which results in weight loss in ulcerative colitis.