What are the things that can be done to intestines to increase surface area?

Reduce inflammation. Its estimated that the small intestine alone has enough surface area to cover between 14 to 20 tennis courts. As such, reduction of intestinal surface area over which to digest and absorb food results in malabsorption. This is often seen with inflammatory conditions like crohn's, celiac disease. Infectious processes may also "blunt" the intestinal villi so surface area drops--as in tropical sprue.