Q. Why are so many foods gluten-free now, is gluten unhealthy?

A. Gluten is a mixture of proteins found in certain cereal grains like wheat, barley, and rye. It’s what allows bread dough to feel elastic when flour is mixed with water. Gluten is a well-known problem for people with celiac disease, an autoimmune disorder that affects both adults and children. Symptoms include gastrointestinal problems, pain, malnutrition, and fatigue. Celiac disease can be diagnosed by a blood test, and the only treatment is a gluten-free diet.

More recently, clinicians have become aware of a population of people who have symptoms of celiac disease but test negative for it. Alessio Fasano, director of the Center for Celiac Research at the University of Maryland, says that these patients have gastrointestinal problems and may have depression, “foggy mind,’’ and other behavioral symptoms. Fasano says these patients feel better when gluten is taken out of the diet, and they get worse again when back on it.

The condition, called gluten sensitivity or gluten intolerance, is still not well understood. Fasano says it seems to be caused by a different type of immune response, and researchers are currently looking for a way to test for the condition. Earlier this month in the journal BMC Medicine, he and several other experts published a consensus statement recommending how to classify gluten sensitivity. If you have symptoms of either condition, the first step is to get tested for celiac disease. Then talk with your doctor about trying a gluten-free diet.