The etiology of colorectal cancer is still unclear, and it is widely recognized that the occurrence of colorectal cancer is the result of a combination of factors. Factors related to the occurrence of colorectal cancer are divided into the following major categories. Diet: Diet is one of the most important factors that cause colorectal cancer. High protein and high fat diet: It is obvious from the observation of colorectal cancer incidence rate that colorectal cancer is closely related to people’s living standard. The incidence of colorectal cancer in developed areas is significantly higher than that in non-developed areas. After undigested protein and fat enter the colon, a large amount of carcinogenic substances are produced by the decomposition of bacteria in the colon, which leads to the occurrence of colorectal cancer. Low-fiber diet: High-fiber diet will reduce the incidence of colorectal cancer. Because of the increase of fiber in food, more stool can dilute carcinogenic substances and stimulate intestinal wall to promote intestinal peristalsis, reducing the time and opportunity for absorption of harmful substances. If a long-term low-fiber diet, the probability of colorectal cancer will be greatly increased. Pickled food: When vegetables are pickled, more of the vitamins they contain are lost, and almost all of the vitamin C is lost. Pickled foods are often contaminated by microorganisms during the pickling process, which can easily induce intestinal lesions. Nitrate in vegetables can be reduced to nitrite by microorganisms, nitrite in the human body when it encounters amines, can generate nitrosamines. Nitrosamines are a carcinogenic substance, so often eat pickled products are prone to cancer. Baked, fried, smoked food: because of repeated high-temperature heating of fats and oils, unsaturated fatty acids produced by high-temperature heating of polymers – dimers, trimers, more toxic. Most fried and baked foods, especially French fries contain high concentrations of acrylamide, a carcinogenic substance. And the cracking products of fish and meat cooked at high temperatures produce mutagens and carcinogens such as dimethylhydrazine, which induces the colon of rats. Lack of essential trace elements in food: Trace elements copper, zinc, iron, selenium, potassium, molybdenum and calcium are all useful in preventing colon cancer, among which copper, zinc, iron and selenium are considered to be essential trace elements with anti-cancer effects. Increased intake of copper, zinc, iron and selenium can prevent the occurrence of colorectal cancer, while excessive intake of phosphorus is a risk factor for the development of rectal cancer. Age: Colorectal cancer is a disease of the elderly, more than 80% of colorectal cancers occur in middle-aged and elderly people older than 50 years old, and the higher the age, the higher the risk of colorectal cancer. Therefore, the aging of the population may be an important reason for the current increase in the incidence of colorectal cancer. Family history of colorectal cancer: There are a lot of studies proving that if one person has colorectal cancer, his immediate family members (parents, children, siblings) are 2-3 times more likely to get colorectal cancer than the normal population. Many patients with colorectal cancer present as a cluster of family offspring. In particular, there is a disease called familial adenomatous polyposis, which is an autosomal dominant disease that often appears during adolescence and has an initial manifestation of extensive polyps in the large intestine, which eventually develop into intestinal cancer if left untreated. The offspring of patients have a 50% chance of inheriting the disease, and once the disease occurs, it will be 100% carcinogenic. Colon polyps are closely related to the development of colorectal cancer, and most colorectal cancers evolve from polyps. However, not all colon polyps are carcinogenic, only adenomatous polyps are prone to cancer, while inflammatory and hyperplastic polyps are generally not carcinogenic. Diseases such as ulcerative colitis and colonic schistosomiasis are closely associated with the development of colorectal cancer. One possible reason is that repeated irritation of the intestine by chronic inflammation induces cancerous changes in the intestinal mucosa. Another pathogenesis is the mutation of proliferating cells in the process of repeated damage and repair of body tissues, which in turn evolves into tumor cells. Smoking: Tobacco produces a large amount of carcinogenic substances during the burning process, which can increase the incidence of many malignant tumors, including lung cancer and colorectal cancer. Previous smoking increases the risk of colorectal cancer. Compared to never smokers, a history of smoking for at least 20 years increases the risk of colorectal cancer by 26%; smoking more than 20g of tobacco per day increases the risk of colorectal cancer by 30%; smoking for more than 30 years or more than 20g of tobacco per day increases the risk of colorectal cancer by 48%. Thus, smoking increases the risk of colorectal cancer, and early cessation of smoking is beneficial to the prevention and treatment of colorectal cancer. Alcohol consumption: Some scholars in China have suggested that alcohol abuse is related to the occurrence of bowel cancer, but it is not clear. Foreign reports have not confirmed that alcohol consumption is related to colorectal cancer.