Etiology of rectal cancer: dietary factors, high-fat foods such as meat, high-protein foods and low-fiber foods such as starch, potatoes and carrots. It has a very important relationship with the incidence of rectal cancer. High-fat diet can not only stimulate the increase of bile secretion, but also promote the synthesis of cholesterol and lithocholic acid in the liver, so it increases in the intestinal cavity and is converted into cholesterol metabolites under the action of colon bacteria. Low fiber food does not absorb water. Reducing the frequency of defecation, increasing the retention of waste in the intestine, prolonging the retention time of feces in the large intestine and increasing the long-term contact between carcinogens and the mucosa of the large intestine have become one of the causes of rectal cancer. Both high fat and low fiber are carcinogens or auxiliary carcinogens, thus increasing the incidence of rectal cancer.