The full answer
The short version
Celiac disease is a chronic autoimmune condition in which eating gluten — a protein found in wheat, barley, and rye — causes the immune system to attack the lining of the small intestine. Over time this damages the tiny, finger-like structures called villi that absorb nutrients, which is why untreated celiac disease so often leads to fatigue, digestive symptoms, and nutrient deficiencies even in people who eat plenty of food.
Why it happens
In someone with celiac disease, gluten triggers an immune response that mistakenly targets the body’s own intestinal tissue rather than just the gluten itself — which is what makes it an autoimmune disease rather than a simple food allergy. The only current treatment is a strict, lifelong gluten-free diet; there is no medication that lets someone with celiac disease eat gluten safely. For a clinical overview, see the NIDDK’s guide to celiac disease.
Important context
Individual symptoms, reactions, medical histories, food products, and local labeling rules can vary. Community experiences are not medical evidence.
For personal medical decisions, diagnosis, testing, or treatment, consult a qualified healthcare professional.