The relationship between food and cancer is complex, but also very important. It is important because more than 30% of cancer deaths are related to dietary factors; it is complicated in two aspects: on the one hand, the harmful components of food have carcinogenic and cancer-promoting effects, and on the other hand, its nutrients have the effect of combating and preventing cancer. First, carcinogenic substances in daily life Medical research has found that there are more than 10 kinds of chemical substances with carcinogenic effects, of which nitrosamines, benzopyrene and aflatoxin are recognized as the three major carcinogens, which are closely related to diet. 1. Nitrosamines can trigger tumors in almost all organs of human body, among which digestive tract cancer is the most common. Nitrosamines are commonly found in cereals, milk, cheese, tobacco and alcohol, smoked meat, grilled meat, sea fish, canned food and drinking water. The content of nitrite is higher in unfresh food (especially vegetables that have been cooked for a long time). 2, benzo(a)pyrene is mainly produced in coal, oil, natural gas and other substances in the combustion process, fat, cholesterol, etc. at high temperatures can also form benzo(a)pyrene, such as sausage and other smoked products in the benzo(a)pyrene content of 60 times higher than ordinary meat. It has been proved that long-term exposure to benzo(a)pyrene can cause lung cancer as well as digestive tract cancer, bladder cancer and breast cancer. 3, aflatoxin is the strongest known carcinogen. Medical doctors believe that aflatoxin is likely to be an important cause of liver cancer. In some areas with high incidence of liver cancer, people often eat fermented foods such as bean curd milk, bean paste, etc., which are easy to produce aflatoxin in the production process if the method is not appropriate. Second, the food cancer ranking 1, pickled food: salted fish produced by dimethyl nitrite, in vivo can be converted to carcinogenic substances dimethyl amine nitrite. Salted eggs, salted vegetables and other carcinogenic substances, should be eaten as little as possible. 2, barbecue food: roast beef, roast duck, roast lamb, roast goose, roast suckling pig, roast lamb kebabs, etc., because of the presence of strong carcinogens should not be eaten. 3, smoked foods: such as smoked meat, smoked liver, smoked fish, smoked eggs, smoked tofu, etc. Containing benzo(a)pyrene carcinogen, often easy to eat esophageal cancer and stomach cancer. 4, fried food: after frying, produce carcinogenic polycyclic aromatic hydrocarbons. When coffee is burnt, benzo(a)pyrene will increase 20 times. Pancakes, stinky tofu, fried taro horn, doughnuts, etc., because most of them use oil that has been repeated many times, and carcinogens will be produced under high temperature. 5, moldy substances: rice, wheat, beans, corn, peanuts and other foods are susceptible to moisture mold, contaminated by mold will produce carcinogenic toxins – aflatoxin. 6, overnight cooked cabbage and sauerkraut: will produce nitrite, in the body will be converted to carcinogenic amine nitrite. 7, betel nut: chewing betel nut is a factor causing oral cancer. 8, repeatedly boiled water: repeatedly boiled water contains nitrite, which generates carcinogenic amine nitrite after entering the human body.