Malignant tumors have become one of the common diseases that endanger human health, and cancer is the second leading cause of death in China, and the trend is increasing year by year. Diet plays an important role in the development of many cancers such as esophageal cancer, gastric cancer, liver cancer, colorectal cancer, breast cancer, etc. The relationship between diet and cancer is briefly reviewed here.
I. Dietary factors that increase the risk of cancer
Pesticides: Pesticide residues are widely used in the production of crops, which cause pollution to the environment and food after use, and pesticides in the environment can also migrate to food through the food chain, resulting in high pesticide residues in food. There are many types of pesticides, including carbamates in recent years there is information reported that such pesticides in weak acid conditions can be generated with nitrite nitrosamines, may have some potential carcinogenic effects, but also mutagenic.
2, dibenzoids: dibenzoids are chlorinated oxygenated tricyclic aromatic compounds, is the emergence of new environmental pollutants in the 1970s, the most representative, the most toxic 2,3,7,8-tetrachlorodiphenyl – to – dibenzoids (TCDD). TCDD is a confirmed human carcinogen, which increases the incidence of cancer.
3. Heavy metals: such as arsenic Due to the use of industrial waste and arsenic-containing pesticides, the environment is polluted by arsenic, which can migrate to food through the food chain. It has been confirmed that a variety of arsenic-containing compounds are mutagenic, which can lead to genetic mutations, chromosomal aberrations and inhibit the repair of DNA damage in vitro and in vivo.
4, food containers, food packaging materials, food additives: food containers, packaging materials such as vinyl chloride monomer, has been confirmed to be a carcinogenic, food additives such as antioxidants butyl hydroxyanisole (BHA), dibutylhydroxytoluene (BHT) also has carcinogenicity.
5, mycotoxins: improper harvesting and storage of food can lead to mold growth. So far, there are more than 200 known mycotoxins, of which there is widespread concern is aflatoxin, aflatoxin is the metabolites produced by Aspergillus flavus and Aspergillus parasiticus, more than 20 species have been isolated, the most carcinogenic is aflatoxin B1 (AFB1).
AFB1 ability to induce liver cancer is 75 times greater than dimethylnitrosamine, is a very strong chemical carcinogen, not only can cause liver cancer in animals, but also in other parts of the tumor, such as gastric adenoma, kidney cancer, rectal cancer and breast, ovarian, small intestine and other parts of the tumor.
Human epidemiological data show that the level of dietary aflatoxin and the occurrence of primary liver cancer is positively correlated, exposure to aflatoxin while infected with hepatitis B virus is a risk factor for liver cancer, reduce the level of aflatoxin in the diet of the population, HBV infection and the incidence of primary liver cancer are on the decline. Aflatoxin is easy to contaminate food peanuts, peanut oil, corn; rice, wheat, flour contamination is light, beans are rarely contaminated.
6, N-nitroso compounds: N-nitroso compounds are a class of compounds with strong carcinogenic effects on animals, 90% of the more than 300 known N-nitroso compounds are carcinogenic, and may be related to the occurrence of human stomach cancer, esophageal cancer, colorectal cancer, bladder cancer.
There is no direct evidence that N-nitroso compounds are carcinogenic to humans, but there is no doubt that they are carcinogenic to animals, either in large doses at one time or in small doses over a long period of time, and no animal has yet been found to be resistant to the carcinogenicity of N-nitroso compounds. vegetables and pickled vegetables are widely present.
7, polycyclic aromatic compounds: polycyclic aromatic compounds, including polycyclic aromatic hydrocarbons (PHA) and heterocyclic amines, are a class of food contaminants with carcinogenic effects, the most representative of which is benzo(a)pyrene. the carcinogenicity of B(a)P to animals is certain, human epidemiological surveys show that the B(a)P content in food is associated with cancer incidence. When food is baked or smoked, the food components are pyrolyzed or thermally aggregated at high temperatures to form B(a)P.
Meanwhile, protein-rich food (such as meat and fish) will produce heterocyclic amines such as 2-amino-3-methylimidazoquinoline, 2-amino-1-methyl-6 benzimidazolopyridine by high temperature decomposition, which are strong mutagenic substances and can cause various tumors such as colon cancer, breast cancer, skin cancer, etc. in experimental animals.
8, dietary structure: poor dietary structure includes high fat, high cholesterol, low fiber and high energy and high carbohydrate diet. A large amount of epidemiological data shows that: high fat diet can significantly increase the incidence of colon and rectal cancer, and research suggests that excessive intake of dietary fat may be related to breast, prostate, bladder and ovarian cancer; dietary cholesterol can increase the risk of lung and bladder cancer; excessive caloric intake and the transformation of excessive caloric energy into fat can increase the risk of breast and endometrial cancer; dietary fiber is important for improving intestinal function and preventing colon cancer. Dietary fiber is important to improve intestinal function and prevent the occurrence of colon and rectal cancer.
9.Dietary habits: eating pickled, fermented and smoked food is closely related to cancer because these foods contain a lot of carcinogens and mutagens; in addition, the incidence of stomach cancer is significantly higher among people who like to eat high-salt diet; of course, alcohol consumption is related to the occurrence of many cancers such as oral cancer, laryngeal cancer, esophageal cancer, breast cancer, colon cancer, rectal cancer and primary liver cancer.
Dietary factors to reduce the risk of cancer
1. Vitamins: including V-C, V-E, carotene and folic acid.
V-C, as an antioxidant, can remove free radicals and plays an important role in protecting DNA, protein and membrane structure from damage; it can also inhibit the formation of nitrosamines from nitrites and amines in the stomach, which has a certain role in preventing stomach and esophageal cancer. V-C also plays an important role in the conversion of folic acid to tetrahydrofolate. Fresh vegetables and fruits are rich in V-C. V-E is an antioxidant that scavenges free radicals and prevents damage to polyunsaturated fatty acids in cell membranes, sulfhydryl-rich protein components in membranes, and the cytoskeleton and nucleic acids by free radicals or oxidants.
Epidemiological data show that low V-E intake increases the risk of cancer, especially lung and breast cancers. foods rich in V-E include vegetable oils, hard fruits, and legumes. Carotene is a carotenoid with mainly V-A pro-activity. Carotenoids have a diene conjugate bond in their molecules and are effective bursting and trapping agents for singlet oxygen, hydroxyl radicals, lipid peroxide radicals and other free radicals.
V-A and its derivatives (e.g. 5,6-epoxyretinoic acid, 13-cis-retinoic acid) may have anti-initiator gene activity because of their ability to promote normal differentiation of epithelial cells and also to prevent tumor formation.
Carotenoids are abundant in carrots, pumpkin, dark green leafy vegetables, tomatoes, and papaya. The active form of folic acid in the body is tetrahydrofolate, which functions as a carrier of one-carbon units in many important biosyntheses in the body. Folic acid can affect DNA and RNA synthesis through adenine and thymidylate, and is involved in the methylation process of initiating tRNA in organelle protein synthesis, which can reduce the risk of cancer. Folic acid is widely found in plant and animal foods, and foods rich in it include liver, kidney, green leafy vegetables and beans.
2.Dietary fiber
It is a polysaccharide in carbohydrates that cannot be digested, including cellulose, hemicellulose, lignin, pectin, gum, etc. Dietary fiber can stimulate the secretion of digestive glands and promote intestinal peristalsis; it can regulate lipid metabolism, promote the discharge of bile acids and neutral steroids, and lower serum cholesterol; it can adsorb certain carcinogenic and cancer-promoting substances and reduce their absorption. Therefore, dietary fiber is important in preventing the occurrence of colorectal cancer. Vegetables and fruits as well as coarse grains are rich in dietary fiber.
3.Inorganic salt
Selenium is an important component of glutathione peroxidase (GSH-Px), which catalyzes the reduction of glutathione in the body and reacts with peroxide redox to protect biofilm from damage and maintain normal cell function. The results of animal experiments prove that selenium supplementation can block aflatoxin-induced primary liver cancer in rats and prevent the occurrence of breast cancer and colon cancer.
Population survey found that the incidence of tumor is significantly higher in selenium-deficient areas, and the incidence of gastric cancer is related to selenium deficiency. Good sources of selenium are animal foods liver, kidney, meat and seafood. Other micronutrients such as low molybdenum can easily lead to digestive tract tumors, iodine deficiency can cause goiter, which can develop into thyroid tumors, and can also promote the occurrence of hormone-related breast cancer, uterine membrane cancer and ovarian cancer.
4.Non-nutrients
Non-nutrients are naturally occurring chemical substances with anti-mutagenic, anti-cancer or other physiological activities in food, mainly found in plant foods, so they are also called phytochemicals, as opposed to nutrients (protein, fat, carbohydrate, minerals).
Representative non-nutrients include phenolic compounds, indoles, sulfhydryl compounds, aromatic spices and phytochromes, terpenoids, porphyrins, protein inhibitors, flavonoids, and saponins. Isoflavones, genistein flavonoids, soy glucosinogen, and protease inhibitors in soybean can delay or prevent tumor development.
Indoles and aromatic isothiocyanates in cruciferous vegetables (e.g., kale, cauliflower, broccoli, cabbage, purple rape) are considered to be the two main types of carcinogenic components of cruciferous vegetables in the form of glycosides. Allium spp. such as garlic, shallots, and leeks have well-documented ability to prevent stomach, colon, and rectal cancers. Citrus spp. contain terpenoids that prevent stomach cancer and likely prevent esophageal, oropharyngeal, and rectal cancers. Mercaptans are widely present in fruits and vegetables, and there are numerous studies showing that green vegetables and other dark-colored vegetables such as carrots have clear cancer-preventive effects.
III. Dietary prevention of cancer
Adopt a balanced diet, diversify food, control the intake of fat, especially saturated fatty acids, increase the proportion of vegetables and fruits and whole grains in the diet, reduce the proportion of animal food (meat and eggs) intake, do not eat mold contaminated or burnt food, eat less pickled, smoked or fried food, drink alcohol in moderation, soak vegetables for 30 minutes and wash them well, peel fruits to reduce pesticide residues. In short, we should try to avoid dietary factors that increase the risk of cancer and strive for dietary factors that are beneficial to cancer prevention.
Diet for cancer patients
From the analysis of recent dietary survey results of cancer patients: the average daily intake of energy and most nutrients per person in all cases is obviously insufficient, among which energy only reaches 69.2% of the supply standard and protein reaches 88.3% (of which high-quality protein accounts for 46.4% of the total protein intake). In addition, the intake of vitamin B2, calcium, phosphorus, zinc and selenium was significantly lower than the supply standard.
Clinically, we have observed that almost all cancer patients have varying degrees of loss of appetite or even anorexia. In addition to the reaction of the disease itself, this is also related to psychological factors such as mental depression and anxiety of patients; plus the stress reaction of the organism to surgery, chemotherapy, radiotherapy and other factors also aggravate the degree of loss of appetite and anorexia of patients. These are the main reasons for cancer patients to eat less.
With the progress of tumor treatment, diet and nutrition therapy occupy a very important position in surgery, radiotherapy, chemotherapy and rehabilitation therapy. Due to various factors such as loss of appetite, anorexia and side effects of anti-cancer treatment, cancer patients have reduced food intake, resulting in different degrees of protein-calorie malnutrition and even cachexia, which is an important cause of death in advanced cancer patients.
Therefore, we must attach great importance to the nutrition of cancer patients, evaluate the nutritional status of patients as early as possible, analyze the causes of their nutritional deficiency, formulate practical nutritional treatment plans and measures, strengthen the inspection and guidance of cooking staff in implementing nutritional treatment plans, and at the same time, give warm comfort, encouragement and dietary guidance to patients so that they can actively cooperate with clinical treatment and nutritional treatment.