About 1 percent of the U.S. population has celiac disease, an autoimmune and digestive disorder. Sufferers are unable to eat gluten—a protein found in rye, barley, wheat, and more—without triggering an attack on their small intestine. Symptoms vary from person to person, but include: abdominal pain and bloating; chronic diarrhea; vomiting; constipation; and pale, foul-smelling, or fatty stool. Doctors typically diagnose it with blood tests and stool samples.
While there's no cure, people can manage celiac disease by adopting a gluten-free diet. Within several weeks, inflammation in the small intestine will subside—though accidently eating a product with gluten could cause a flare-up at any time.