Gluten is composed of gliadin, a substance found in wheat, barley, and rye products. Celiac disease is an immune-mediated disorder that develops as a result of ingestion of those products. Those with the disease have increased levels of antibodies that have an inflammatory response manifested by loss of intestinal villi. (It is unknown whether antibodies are produced primarily or secondarily to tissue damage.) This causes malabsorption and can lead to severe malnutrition in infants and elderly. People with eating disorders who have celiac disease are especially at risk.