Fiber is the part of fruits, vegetables and grains not digested by your body. A low-fiber diet restricts these foods. As a result, the amount of undigested material passing through your large intestine is limited and stool bulk is lessened.A low-fiber diet may be recommended for a number of conditions or situations. It is sometimes called a restricted-fiber diet.PurposeYour doctor may prescribe a low-fiber diet if: You have narrowing of the bowel due to a tumor or an inflammatory disease You have had bowel surgery You are having treatment, such as radiation, that damages or irritates your digestive tractAs your digestive system returns to normal, you usually can slowly add more fiber back into your diet.