Celiac disease is a digestive disorder that occurs in reaction to gluten, a protein found in rye, barley, wheat, and hundreds of foods made with these grains. The body's immune system reacts to the gluten and causes damage to the intestine. Celiac disease, also known as celiac sprue or gluten-sensitive enteropathy, is fairly common. One in 133 Americans has the disorder and needs to follow a gluten-free diet.