Since high school, 38-year-old Oakland resident Laura Linden experienced chronic, mysterious stomach pain. It became gradually worse over the years. A couple of times, while the doe-eyed blond was an undergrad at UC Davis, the pain got so bad that she took herself to the emergency room. Once, she overheard a health worker remark that she probably had an eating disorder.

Nothing was further from the truth. Although Linden ate a lot, she could never accumulate much more than 110 pounds on her five-foot-four-inch frame. She figured the cause of her malaise was in her blood. As a kid, she'd watched her mom pop Rolaids like candy. "I used to think to myself, 'Yeah, if you cut up my mom's veins there's probably chalk inside," she joked recently over a bowl of taco salad at a Berkeley raw-foods restaurant.

Things got worse for the former journalist about ten years ago. She was exhausted all the time, and had frequent allergy attacks, colds, and sinus infections. Doctors viewed her symptoms in isolation. Sour stomach? Cut out orange juice and coffee. Sinus infection? Here are more antibiotics. But her constant sickness took its toll.

"I kind of knew something was wrong with me," Linden recalled thinking. "But at the same time, I also kind of bought this idea that maybe it was just me, maybe this was how it was supposed to be, or maybe I'm a stress case or something like that."

Her health deteriorated further a few years ago, as she attended grad school at the University of Arizona. Finally, Linden went to a campus doctor complaining of fatigue and a bad cold. After a series of tests, the results were clear: Linden had celiac disease, an autoimmune disorder that prevents the body from processing gluten, a protein found in wheat, barley, and rye. She had never heard of it before.

The doctor's prescription: a gluten-free diet for life.

That might have seemed daunting, but Linden was overjoyed. "I just cried!" she said. "I couldn't believe it 'cause I didn't really think that there was a thing that I was going to stumble across that was going to make me better."

As her gastroenterologist probed into her past, he found more than a few indications of the disease, such as the wart-like growths she would get in the corners of her mouth in junior high — a sign of malnutrition. But up until that point, doctors never thought to screen her for celiac. "It's not like I had cancer or I was bleeding to death, so there's nothing very obvious," Linden rationalized.

These days, she hardly resembles the sickly girl she describes. She still has some digestive problems, but her weight is back up — "probably more than I want it to be," she said — along with her energy. She even works out at the gym these days.

Linden never suspected something as seemingly innocuous as bread could make her sick. Yet foods containing wheat, rye, or barley prompted her body to attack itself. Her own antibodies would inflame and damage the tiny, finger-like villi in her small intestine. The absence of these nutrient-absorbing structures explained why Linden was malnourished and often doubled over in pain.

She was one of the lucky few to be diagnosed. Researchers believe millions like her still suffer needlessly.

Chances are you know someone who has celiac, but even better that they don't know it. Although the numbers vary, researchers estimate that celiac affects about 1 in 133 Americans, and that a staggering 97 percent are undiagnosed. A large-scale study in 2003 estimated there were about fifteen thousand diagnosed celiac patients. This year, that number is expected to exceed one hundred thousand, said Michelle Pietzak, a pediatric gastroenterologist, assistant professor of clinical pediatrics at USC's Keck School of Medicine, and one of the authors of the 2003 study.

For each person diagnosed with celiac, another 140 will seek medical attention for twelve years before receiving a diagnosis, Pietzak said.

The disease has only recently gained attention in the United States. Last November, CNN anchor Heidi Collins became a spokeswoman for the National Foundation for Celiac Awareness. Articles in The New York Times, Newsweek, and Time have helped raise its profile. And in 2004, the National Institutes of Health convened its first meeting on celiac. Yet there still hasn't been much of an increase in diagnoses, said Elaine Monarch, founder and executive director of the nonprofit Celiac Disease Foundation.

The condition goes undiagnosed for a number of reasons. For one, most medical texts touch on it only briefly, and even then it's described as a rare childhood disorder. This perception became a self-fulfilling prophecy, the Wall Street Journal revealed in 2005, because doctors tended not to test for celiac. And because the condition is related to malnutrition, doctors erroneously ruled out patients who were overweight or obese.

It also can be a tricky diagnosis, since symptoms vary, and some people don't have any. Among the most common, according to the Celiac Disease Foundation, are a distended stomach, cramps, excessive gas, bloating, chronic diarrhea, constipation, anemia, fatty stools, and weight loss. Celiacs can also be depressed, irritable, lacking in energy, infertile, have dental enamel defects, and develop osteoporosis, joint pain, ulcers, or a blistering, itchy skin rash called dermatitis herpetiformis.

Actually getting a diagnosis is fairly straightforward. A blood test taken when the patient is on a gluten-containing diet checks for the presence of antibodies. The disease is confirmed by an intestinal biopsy that demonstrates damage to the villi.

As far as researchers know, celiac has been around since humans switched from a foraging diet of meat and nuts to a cultivated diet that included grains. Back in the second century, a Greek physician named Aretaeus first dubbed it koiliakos, which meant "suffering in the bowels." Eventually, it became coeliac or "celiac."

While the cause is not well understood, researchers know it is linked to gene variations known as HLA-DQ2 and/or HLA-DQ8. Immediate family members of celiac patients have a 10 percent chance of having it, too, said Douglas Corley, a gastroenterologist and researcher at Kaiser Permanente in San Francisco.

The disease is believed more common among people with disorders such as Addison's disease, Down syndrome, fibromyalgia, lupus, and autism. Even so, only a small percentage of these patients are co-diagnosed as celiac.

It also appears to be more common among people of European descent, Corley said, but that's where it has been looked for most aggressively. Celiac is often activated by traumatic events such as surgery, pregnancy, childbirth, viral infection, or severe emotional stress.

It's not clear whether ingesting gluten causes a person to develop celiac or simply triggers symptoms of the disease. But even the gluten connection wasn't known until 1950, when Dutch pediatrician Willem Dicke noted that British children suffering from chronic diarrhea had thrived during the grain shortages of World War II.