Too Little Intestine. Certain medical conditions require emergency removal of a significant amount of the small intestine. We see this in infancy associated with necrotizing enterocolitis and in adults when the blood supply to the small intestine is cut-off. The small bowel is responsible for digesting nutrients within our diet; if a lot of the small intestine is missing, nutritional deficiencies occur.
Surgery. Surgical removal of the majority of the small intestine is what causes short bowel syndrome.
Loss of intestine. The most common cause of short bowel syndrome is "short bowel" - meaning that you have lost some portion of your intestine. Generally, the more you lose, the worse the condition. Eventually, you can develop intestinal failure where the remaining intestine provides inadequate absorption to maintain hydration and nutrition. Then, the patient will need fluids or TPN or intestine transplantation.