According to Beyond Celiac "Celiac disease is an autoimmune disease that's triggered by consuming gluten and results in damage to the small intestine. When a person with celiac disease eats gluten, the immune system sees gluten as a threat and mounts an attack. However, it ends up damaging the villi of the intestines, which help to digest food. Damaged villi make it nearly impossible for the body to absorb nutrients, leading to malnourishment and a host of other issues."