The exact cause of celiac disease is unknown. The lining of the intestines contains areas called villi, which help absorb nutrients. When people with celiac disease eat foods or use products that contain gluten, their immune system reacts by damaging these villi. This damage affects the ability to absorb nutrients properly. A person becomes malnourished, no matter how much food he or she eats. The disease can develop at any point in life. People who have a family member with celiac disease are at greater risk for developing the disease. The disorder is most common in Caucasians. Women are affected more often than men.

The symptoms of celiac disease differ by person. This complicates diagnosis. Gastrointestinal symptoms include: abdominal pain, bloating, gas, or indigestion, constipation, decreased appetite, diarrhea, lactose intolerance, nausea and vomiting, stools that float, are foul smelling, bloody or “fatty”, and unexplained weight loss. An upper endoscopy may be performed to biopsy from the first part of the small intestine (duodenum). The biopsy may show a flattening of the villi in the parts of the intestine below the duodenum.