Celiac disease is like this autoimmune condition where your body totally freaks out when you eat gluten, which is this protein found in wheat, barley, and rye. It's like your immune system goes to war against your own small intestine, and that's no good! It messes with nutrient absorption, leading to all sorts of problems—like losing weight even when you don't want to, or just feeling miserable after eating. So, about 1% of people have this condition, which is kind of wild, but it's a serious thing. If you're one of those people, going gluten-free isn’t just a fad; it's a must!