The surface area of the small intestine in a healthy person is really large! The reason for this is the villi covering the inside of the small intestine. We need all this surface area to absorb the nutrients from our food. When a person has coeliac disease, antibodies attack the villi and cause them to flatten. This means we have much less surface area to absorb nutrients, glucose for energy and amino acids from our food which help us to build new protiens. These are all things we need to grow.