Diet Plan for Anal Fistula Anal fistula is a narrow tunnel with its internal opening in the anal canal and its external opening in the skin near the anus. If there is infection in the anal canal a channel is build and there is oozing of pus. The tract formed by this process is called fistula. It is very irritating and painful because of drainage of pus. Low fiber diet, poor and unhealthy life style and stress are the main