Q. My niece has to avoid wheat because it makes her sick. What does she have?

A. She may have celiac disease, where the cereal protein gluten, also found in rye and barley, causes her immune system to damage the lining of her intestines, leading to diarrhea, weight loss, fatigue, abdominal cramps, distention, bloating after meals, constipation or vomiting.

But many celiacs don't have these intestinal symptoms, and instead have unexplained irondeficiency anemia, poor growth, delayed puberty, poor coordination, infertility, dental enamel disease, thin bones, or a rare rash called dermatitis herpetiformis: groups of small, itchy blisters over the elbows, knees, scalp or back.

Rare celiacs may only have headaches and unsteadiness.

People with repeated abdominal pain who are malnourished, have mood changes or have anemia may have celiac disease. It is especially common in Type 1 (juvenile, or insulin-dependent) diabetics and in Down syndrome.

It is uncommon, occurring in about one in 150 people, but occurs in about one in 50 in those with symptoms, which can begin in infancy, childhood or adulthood. Symptoms often disappear temporarily in teenagers. Celiacs must avoid anything containing gluten, such as beer, bread, bagels, pasta, pizza, malted breakfast cereals and crackers.

Celiacs should read food labels and avoid things with bran, gluten, bulgur, couscous, kamut, spelt and so on — and avoid oats, at least initially. Though 90 percent will improve in two months, about 10 percent take two years to improve. Celiacs should also see a dietitian, and check out www.csaceliacs.org.

Physicians must establish the diagnosis first with blood tests and often a small bowel biopsy. And these tests may be normal if you've been avoiding gluten, so try to eat enough whole-wheat bread or cereal to — yes, get sick again for three or four weeks — so these tests will be more accurate.

It could be that your niece has wheat allergy, which like other food allergies would cause tingling of the mouth, swelling of the tongue and throat, trouble breathing, itchy hives, vomiting, stomach cramps or diarrhea within two hours of ingestion, and can be fatal. Wheat allergy is also uncommon, occurring in less than 1 percent of the population, though it is more common in infants and toddlers.

Most children will outgrow allergies to wheat, milk, egg and soy. But allergies to peanuts, tree nuts, fish and shrimp usually persist. And unlike celiacs, wheat-allergic patients can still eat rye and barley.

So not everyone should be eating Wheaties every morning.

Dr. Landis Lum is a family-practice physician for Kaiser Permanente and an associate clinical professor at the University of Hawai'i's John A. Burns School of Medicine. Send questions to: Prescriptions, Island Life, The Advertiser, P.O. Box 3110, Honolulu, HI 96802; islandlife@honoluluadvertiser.com; or fax 535-8170. This column is not intended to provide medical advice.