Celiac disease is an inherited condition that damages the small intestine and interferes with nutrient absorption. People with this disease cannot tolerate a protein called gluten, which is found in wheat, rye, and barley. Several symptoms affecting the digestive system or other parts of the body are associated with celiac disease, such as diarrhea, abdominal pain (or stomach pain), irritability, and depression. People with the disorder must follow a gluten-free diet for the rest of their lives.