Consumption of 10g of dietary fiber per day will reduce the incidence of colorectal cancer by 10%. A large European epidemiological study showed that dietary fiber intake was negatively associated with the development of colorectal cancer and was not related to the source of dietary fiber. A larger number of prospective clinical trials have found a preventive effect of high-fiber foods. Patients with progressive CRA have reduced dietary fiber intake and their fecal content of various short-chain fatty acids (including butyrate) is decreased. Meta-analysis of the preventive effect of dietary fiber has also confirmed its clinical preventive value. Several observational studies have shown that excessive alcohol consumption will significantly increase the incidence of colorectal cancer, and the correlation is stronger in men. Milk intake had a non-linear negative correlation with colorectal cancer incidence and its protective effect was most pronounced in the highest intake group. People with low calcium intake and those at high risk for colorectal cancer should increase their calcium intake by consuming dairy products low in saturated fatty acids, such as low-fat milk, cheese or yogurt. The above dietary composition study subjects are mostly single and may be influenced by many factors, and studies with large sample populations are still needed to produce more reliable results. Screening The importance of screening is undeniable, and even a single screening sigmoidoscopy has been shown to reduce the incidence of colorectal cancer. It includes questionnaires, fecal occult blood test, sigmoidoscopy or total colonoscopy, and CT reconstruction imaging of the intestine. The first step of screening is to detect and identify the high-risk groups of colorectal cancer. The high-risk groups include: ① Age > 50 years old. ②Patients with the following diseases and their first-degree relatives, adenomatous polyp syndrome, familial adenomatous polyposis, misshapen polyp syndrome, Peutz-Jeghers syndrome, Juvenile adenomatous polyposis (syndrome), hereditary non-polyposis colorectal cancer, colorectal cancer, IBD especially UC or chronic granulomatous colitis. ③People with the following medical history, such as history of colorectal cancer, history of CRA, pelvic radiation therapy, non-tumor surgical treatment (cholecystectomy and ureterosigmoid anastomosis). ④ Those with positive fecal occult blood by immunoassay or chronic diarrhea, frequent mucous bloody stools or chronic constipation. In addition, it should be noted that schistosomiasis endemic areas are also areas with a high incidence of colorectal cancer. The annual cancer rate in the first 10 years after UC is about 2 per 1000, in the second 10 years it is 12 per 1000; the cumulative cancer rate in 10 years is 2%, in 20 years it is 8%, and in 30 years it is even up to 18%. For this reason, the Multidisciplinary Colorectal Cancer Task Force of the American Gastroenterological Association and the Endoscopy Society developed the “Guidelines for Early Detection and Surveillance of Colorectal Cancer and Adenomatous Polyps (2008)”. Colonoscopy allows visualization of the entire colorectal mucosa and removal of polyps. However, colonoscopy is not the “gold standard” without defects, and even for CRA with a maximum diameter of >10 mm, the leakage rate can be 6-12%, while the leakage rate for cancer is about 5%. Reasons for missed diagnoses include technical problems such as poor bowel preparation, incomplete examination, too fast retraction, or polyps hidden in folds. Special techniques to identify them, such as chromoendosocpy and magnified colorectoscopy, can improve the detection rate. The detection rate of CRA can be significantly improved with a colorectoscopy retraction time >6 min.