Celiac disease is a digestive disease that damages the small intestine because of a sensitivity to gluten, which is found in wheat, rye, barley, and oats. Celiac disease is a hereditary disorder that interferes with the absorption of nutrients from food. When people with celiac disease eat foods containing gluten, their immune system responds by damaging the delicate inner surface of the small intestine. Tiny fingerlike protrusions, called villi, line the small intestine and enable the absorption of nutrients from food into the bloodstream. People with celiac disease lose these villi. Without them, malnutrition occurs, regardless of how much food a person consumes. Celiac disease is more common in people of European ancestry and Caucasians. More than 2 million Americans have been diagnosed with celiac disease; however, recent studies have suggested that as many as one in every 133 Americans may have it, and that the disease is underdiagnosed. Celiac disease is a genetic disease that runs in families. A person can have the disease and not know it until it is triggered by severe stress, pregnancy, surgery, physical injury, infection, or childbirth. Celiac disease affects people in different ways. Some people may develop symptoms as children, whereas others do not experience symptoms until adulthood. Some may have diarrhea and abdominal pains, while others have irritability or depression with the onset of the disease. Sometimes, people with celiac disease are asymptomatic, as the undamaged part of the small intestine is still able to absorb enough nutrients. However, these people are still at risk for complications of the disease. Celiac disease can be hard to diagnose. Its symptoms are similar to those of other digestive diseases such as Crohn's disease, irritable bowel syndrome, ulcerative colitis, diverticulosis, and intestinal infections. In addition to a complete medical history and physical examination, diagnostic procedures for celiac disease may include blood work to measure the level of antibodies to gluten or a biopsy. To diagnose celiac disease with a biopsy, the doctor may remove a tiny piece of tissue from the small intestine to check for damage to the villi. During the procedure, the physician eases a long, thin tube called an endoscope through the mouth and stomach into the small intestine. A sample of tissue is then taken using instruments passed through the endoscope. This procedure is considered the gold standard for diagnosing celiac disease. A gluten-free diet is the only treatment for people with celiac disease. Adhering to a gluten-free diet is a lifetime requirement, as eating any gluten will further damage the intestine. For most people, eliminating gluten from their diet will stop symptoms, heal intestinal damage that has already occurred, and prevent further damage. Usually, a person will see an improvement in symptoms within days of starting the diet. Within three to six months, the small intestine is usually completely healed. For older people, complete healing may take up to two years.