What is celiac disease? In my opinion, the first and most important thing to know is that celiac disease is not a wheat allergy, but an autoimmune disease. Simply put, people with celiac disease cannot tolerate gluten, a protein found in wheat, barley, and rye. When gluten enters their body, their immune system mistakenly starts attacking their own healthy tissues. In other words, if the immune system were a security guard, in people with celiac disease that guard mistakes gluten for a dangerous intruder and immediately starts fighting it. Unfortunately, this “fight” happens in the small intestine, where it damages the tiny finger-like structures called villi, which help absorb nutrients from food. Over time,…