Inflammatory Bowel Disease. Inflammatory bowel disease, IBD, is a condition that causes irritation and ulcers in the gastrointestinal tract. It is a group of inflammatory conditions of the large intestine and, in some cases, the small intestine. The most common for IBD are ulcerative colitis and Crohn's disease. Anemia caused by iron deficiency due to gastrointestinal blood loss and reduced iron absorption due to inflammation is often present. It may also be exacerbated by a restrictive diet.