It seems a lot of people with no prior history of gluten intolerance suddenly came down with celiac disease in 2010. (In all fairness, better screening properly diagnosed thousands of people who didn’t know they had it.) Brought on by a gluten protein found in wheat, the autoimmune disease can wreak havoc on the small intestine, causing diarrhea and fatigue. The answer? Avoid all foods containing gluten. The fad? Less than one percent of Americans have the disease, but sales of gluten-free foods have skyrocketed, leading one gluten-free specialty brand to sell for $22 million in December.