They lose the ability to gain nutrients.
Hence, people with celiac disease cannot tolerate gluten. Gluten is a type of protein found as nutrient in food and is released to the digestive system. When the body receives food that contains gluten (e.g. wheat, rye, and barley) the immune systems responds and attacks the small intestines. In the event of this, the linings of the small intestine called villi are damaged. When the villi get damaged, the body cannot properly absorb nutrients.
