Walk into any natural-foods store these days and you’re likely to find a special section stocked with gluten-free foods: pasta made from rice, teff-flour cookies, quinoa-and-amaranth crackers. Even major supermarkets now carry alternative goodies containing no wheat, barley, or rye—and with the gluten-free products market growing at about 17 percent per year in the U.S., you’ll soon see many more such items. A rash of new books from major publishers—with titles like 1,000 Gluten-Free Recipes (Wiley, fall 2008), Gluten Free, Quick and Easy (Avery, summer 2007), and even Living Gluten-Free for Dummies (For Dummies, 2006)—are slated for release or are in stores now. So what on earth is gluten? And why are people avoiding it?

Gluten is the protein found in wheat, barley, and rye—as well as several less-common related grains—that gives them the ability to stick together and form doughs and batters. Recent research indicates that at least one in 133 people has celiac disease, a genetic condition that makes them unable to digest gluten. For celiac patients, eating foods with gluten can damage the lining of the small intestine, leading to digestive discomfort, inflammation, and malabsorption of nutrients—which in turn can trigger other health problems, such as osteoporosis, skin rashes, and infertility.

Doctors speculate that there are even more undiagnosed celiacs out there, and that others may be sensitive to gluten without having full-fledged celiac disease. “Some people just feel better when they don’t eat gluten, and that may mean that they don’t digest it very well,” says Joseph Murray, a doctor and celiac disease researcher. Symptoms of gluten intolerance are similar to but less severe than celiac symptoms and can include digestive discomfort and inflammation.

One reason that gluten intolerance is on the rise may be growing dietary concerns among the public. “The medical community is slowly becoming more aware of the problem, but that pales in comparison to the public’s awareness of how food affects us,” says Stephen Wangen, a naturopathic doctor based in Seattle. Recent fads like low-carb and raw-food diets require people to cut out wheat and other grain products; some experts think these diets may have led some people to realize they felt better when they avoided gluten. The market for gluten-free goods is expanding among non-celiac sufferers, too, as a growing number of people remove gluten from their diets even without a diagnosis.

Developing gluten-free crackers, cookies, and other products involves much trial and error. Specialty flours made from gluten-free foods like rice and corn, or “heritage” grains like sorghum and quinoa, must be coaxed into forming dough, which rarely bakes with the same texture as wheat flour. So a binding agent, like xanthan or guar gum, is added to give gluten-free baked goods the same elasticity and feel as those that contain gluten. The catch is that every single ingredient has to be processed in a gluten-free facility to be considered uncontaminated, because even a trace of wheat, barley, or rye can trigger a reaction in gluten-sensitive people.