Number of Americans who are unaware they have celiac disease, according to a recent Mayo Clinic study. About 1.8 million people in the U.S. have celiac disease, an autoimmune condition that causes pain, diarrhea and eventually malabsorption of nutrients when people eat foods containing the protein gluten, found in wheat, barley and rye. Aside from the 1.4 million Americans who remain undiagnosed, another 1.6 million people are on a gluten-free diet even though they don’t have celiac disease. “It’s not clear what the medical need for that is,” said study author Dr. Joseph Murray in a statement. [via Mayo Clinic]