When a person with celiac disease eats any of these grains, a protein called gluten found in them causes a reaction in his or her immune system. The immune system damages the tiny, fingerlike projections, called villi, that line the small intestine. Villi are important because nutrients pass through them into the bloodstream. When villi are destroyed, the person becomes malnourished, no matter how much food he or she eats, the NIDDK says. The person has difficulty absorbing carbohydrates, fat, protein, fat-soluble vitamins, calcium, magnesium, iron, folate, and zinc.

Celiac is a genetic disease, meaning it runs in families. It is classified both as an autoimmune disease (because the body's immune system attacks the small intestine) and a disease of malabsorption (because nutrients are not absorbed), the NIDDK says. The disease can develop in children and in adults, although it's unclear who will develop it when. Breast-feeding appears to delay symptoms in children. The longer a child is breast-fed as an infant, the later symptoms will develop.

This form of sprue is found in some tropical areas, such as the Caribbean, India, and Southeast Asia. Researchers aren't sure of the exact cause, but they suspect some kind of infection, including all of those listed (bacteria, viruses, parasites, or contaminated food), or conditions such as vitamin deficiency. The main symptoms of tropical sprue are diarrhea, weight loss, and anemia. Treatment usually is a course of antibiotics.

All of the diseases listed are autoimmune diseases, as is celiac disease. Other autoimmune diseases that may occur along with celiac disease include dermatitis herpetiformis, collagen vascular disease, and Sjogren's syndrome. Researchers suspect that the link between celiac disease and these other autoimmune diseases is genetic.

Other symptoms of celiac disease, according to the NIDDK, include weight loss, foul-smelling stools, gas, bone pain, behavior changes, delayed growth (in children), failure to thrive (in infants), joint pain, seizures, tingling numbness in the legs, tooth discoloration, and infertility. Symptoms differ from person to person; some have only abdominal symptoms, others have behavioral changes. Children with celiac disease often are irritable. Some people with this disease have no symptoms, because they still have undamaged parts of their small intestine that are able to absorb enough nutrients. These people are still at risk for complications.

A person with celiac disease has higher than normal levels of certain antibodies. These antibodies can be measured with a blood test. If symptoms and the blood test suggest celiac disease, the NIDDK says, the doctor may then order a biopsy of the small intestine. The biopsy checks for damage to the villi. Without these tests, celiac disease is difficult to diagnose because its symptoms are similar to those of irritable bowel syndrome, Crohn's disease, ulcerative colitis, diverticulosis, chronic fatigue syndrome, and depression.

A person with celiac disease must avoid any foods that contain gluten. For most people, a gluten-free diet will stop symptoms, heal intestinal damage, and prevent further damage, the NIDDK says. The healing process can take from six months (children) to two years (adults). This special diet must be followed for the rest of the person's life, because eating any amount of gluten can damage the small intestine. Some people with celiac disease have a small intestine so damaged by the disease that it cannot heal even with a change in diet. These people may need intravenous supplements, the NIDDK says.

These foods do not contain wheat gluten and so are safe to eat. In addition, flours made from these foods and corn grains are available for baking and cooking. Gluten-free products are also available. Other foods that are safe to eat include plain meat, fish, fruits, and vegetables. Should a person with celiac disease eat oats? Some experts say oats are fine, but others recommend against eating oats, because some people with celiac disease have a reaction to oats. You should check with your health care provider or dietitian before trying oats. Commercial food products may contain gluten in the form of additives, preservatives and stabilizers, the NIDDK says. This can also apply to nonfood items such as medicines and mouthwash.

Two types of cancers, lymphomas and adenocarcinomas, can develop in the small intestine of a person with celiac disease, the NIDDK says. Because it may be difficult for a person with celiac disease to absorb enough calcium, osteoporosis may develop. Because of poor absorption of nutrients, a woman with celiac disease who is pregnant may be at risk for miscarriage, as well as neural tube defects and other congenital defects. Seizures may be caused by poor absorption of folate. Poor absorption of folate and iron may cause anemia.