Vegetables, fruits and fiber in food have a protective effect. Eating more fresh fruits, vegetables, antioxidant-rich, vitamin-rich and natural foods can reduce the risk factors of stomach cancer. Moreover, attention to diet, popularization of household refrigerators and reduction of salt intake have immediate effects on reducing the incidence and geographical distribution of gastric cancer. (i) High-fiber diet Epidemiological surveys have shown that dietary fiber can reduce the risk of gastric cancer. In a retrospective case-control study in Sweden, a multi-factor regression analysis of 63 foods and beverages revealed that dietary fiber content was negatively correlated with gastric cardia adenocarcinoma, and the highest group of total fiber content in food (mean: 21.3 g/d) reduced the risk of cancer by 60% compared with the lowest group (8.0 g/d); further analysis was mainly cereal plant (containing cereals and wheat) fiber, and the highest group (mean. 14.7 g/d) reduced the risk of cancer by 70% compared to the lowest group (1.5 g/d). A case-control study in Mexico showed a statistically significant difference in the antagonistic effect of dietary fiber (OR 0.22, 95% CI 0.09-0.55) on gastric cancer. The mechanism by which cereal plant fiber reduces gastric carcinogenesis: saliva is the main source of nitrite entering the stomach, and our daily intake of ascorbic acid, O2 swallowed into the air can convert nitrite to NO thereby preventing the formation of carcinogenic nitrosamines, which has been demonstrated in animal models; the lack and insufficiency of ascorbic acid predisposes tricyanate in saliva to local formation of nitrosamines at the gastroesophageal junction, while cereal Plant fiber has a strong scavenging effect on nitrosamines in an acidic environment and can significantly reduce the concentration of nitrite in the stomach as well as ascorbic acid. Cereal plants contain not only fiber but also whole grains of antitumor components such as: phytoestrogens, phenolic complexes, antioxidants, anti-starch and oligosaccharides. The protective effect of fiber is independent of the tissue type of gastric cancer. (ii) Coffee and tea Epidemiological data show no significant relationship between coffee and black tea and the risk of gastric cancer. Tea is one of the natural cancer prevention agents that have recently received considerable attention. Recently, it has been reported that the incidence of tumors is very low in green tea producing areas and regions or ethnic groups that have tea drinking habits. The results of worldwide retrospective studies on green tea vary, with some reports suggesting that it can reduce the risk of stomach cancer, mainly because of the protective effect of the high concentration of polyphenols contained in green tea. Chinese Academy of Sciences conducted in vivo and ex vivo tests, showing that tea has the effect of blocking the synthesis of nitroso compounds, and showed a significant dose-response relationship; human experiments confirmed that daily consumption of 1 to 5 grams of tea tea, can significantly block the synthesis of nitrite in the body. Beijing Medical University reported that green tea contains a variety of nitrosation inhibitors such as vitamin C, vitamin E and tea polyphenols. Studies have shown that 4.65 g of tea water (equivalent to 32 g of green tea) extract can completely block excessive N-nitrosoproline synthesis in the body of high-risk individuals. The opposite has also been reported, such as two prospective studies in Japan that both concluded negatively and concluded that the low intake of green tea in patients with gastric cancer in a retrospective survey was due to their abdominal symptoms 2 years prior to definitive diagnosis. The World Cancer Research Foundation concluded that no beverage could increase or decrease the risk of gastric cancer. Thus, the anti-cancer effect of green tea needs to be further confirmed, and a larger study is underway in China. Green tea may be a more ideal beverage to prevent the occurrence of gastric cancer. (iii) Spices and condiments Garlic has a wide range of anti-tumor effects. A large number of epidemiological and case-control studies at home and abroad have shown that garlic has inhibitory effects on stomach cancer, intestinal cancer, head and neck tumors, lung cancer and prostate cancer. Randomized controlled studies in northern China have shown that garlic foods, when consumed regularly, can reduce the relative risk of gastric cancer by 53% compared to those who do not consume them. The inhibitory effect of garlic on gastric cancer was found in both retrospective comparative and disease-control and prospective studies. This phenomenon can be seen when the annual consumption of garlic exceeds 2.5 Kg. According to data from Shandong and Beijing, the annual amount of garlic was significantly negatively correlated with the incidence of gastric cancer. Experimental studies have shown that garlic can inhibit the synthesis of N-diethylnitrosamine. The consumption of garlic increases the acid secretion function of the stomach . The level of nitrite and the detection rate of fungus or bacteria in the stomach were significantly decreased. Garlic has a killing effect on bacteria, especially Hp, and the thiosulfate in garlic can inhibit the growth of Hp. Garlic is rich in flavonols, especially tetrahydroxyflavonoids, which contribute to the detoxification of carcinogens. Garlic extract can inhibit tumor growth, and allicin can not only kill individual cultured gastric cancer cells, but also inhibit gastric cancer transplanted in vivo. Earlier, garlic was found to inhibit the early stage of tumor formation in mammals due to its richness in selenium, and then animal experiments confirmed that garlic extract bispropyleneglycoside and propyleneglycoside methyl trisulfide could inhibit tumorigenesis. Recently, Schaffer et al. demonstrated that sulfur-containing complexes in garlic can protect DNA in mammalian epithelial cells. Garlic is abundant in Cang Shan County, Shandong Province, where residents have a habit of eating garlic all year round, and the mortality rate of gastric cancer is only 1/12 of that in Qixia County, Shandong Province, a county with a high incidence of gastric cancer. Therefore, garlic is likely to be a more desirable food to intervene in gastric cancer development. The Italian study concluded that chili peppers and spices are not associated with gastric cancer, probably because the spice consumption lifestyle is mainly in the low incidence southern region; in contrast, chili peppers were reported as a high risk factor in Mexico, where chili pepper spices have a mutagenic effect. Olive oil reduces the risk of gastric cancer, probably because of its antioxidant content, but it is also thought to be related to its use in Mediterranean countries mainly in lettuce salads. In China vegetable oil is thought to reduce the risk of stomach cancer. (iv) Vitamins and trace elements The main vitamins are β-carotene (β-C), vitamins A, C and E (VA, C and E) and folic acid (FA). As early as 1942, Tannock observed the relationship between VA and cancer, he gave tumor-bearing animals treated with radiation using VA, resulting in a 25% reduction in the amount of exposure required to control tumors; Wold et al. used about 16,000 people in a prospective study, focusing on 86 cancer patients and 176 non-cancerous people, the results suggest that low serum levels of VA are associated with cancer incidence, and to lung and gastrointestinal cancers were the most pronounced; Ren Dalin et al. of Tianjin Medical College investigated the relationship between serum VA and gastric cancer incidence in 97 pairs of case controls and found that VA levels were significantly lower in the gastric cancer group than in the control group, and there was a significant dose-dependent relationship between VA levels and the risk rate of gastric cancer. The relationship between β-C content and gastrointestinal cancer confirmed that high dietary β-C intake was associated with gastric and esophageal cancer. between 1985 and 1992, La-Vecchia selected 723 cases of gastric cancer and some non-tumor benign gastrointestinal lesions for the investigation of nutritional elements and gastric cancer risk, and found a direct relationship between β-C, VC and gastric cancer occurrence. Several case-control studies at home and abroad showed that gastric precancerous lesions were also related to vitamin deficiency: Zhang et al. investigated 600 people aged 35-64 with precancerous conditions in a high incidence area of gastric cancer had significantly lower levels of β-C, VC and VE. In Shandong province, a high incidence area for gastric cancer in China, lower concentrations of VC and β-C in blood were found in patients with intestinal hyperplasia of the gastric mucosa. Several studies have confirmed that intake of β-carotene (or carotenoids) reduces the risk of gastric cancer, and it was confirmed in prospective sample intervention studies that neither carotene, VitA nor β-C-converted VitAol were associated with chronic atrophic gastritis. Domestically, in Lin County, Henan Province, an area with a high incidence of esophageal and gastric adenocarcinoma, a homogeneous diet and deficiency of trace elements such as riboflavin, VA, and VC were found to be among the etiological factors. In a subsequent prospective intervention study, the high-risk group was divided into four groups and given different micronutrients with a four-year follow-up. It was found that the administration of VE, β-C and selenium significantly reduced the incidence of gastric adenocarcinoma and the mortality rate by 21%, suggesting that people in the high-incidence area are vulnerable to gastric adenocarcinoma due to lower intake. Folic acid is a water-soluble B vitamin with the following components: glutamic acid, p-aminobenzoic acid and pterostilbene. In China, FANG Jingyuan et al. found that pharmacological doses of folic acid slowed the rate of gastric cancer induced by the interventional carcinogen ethylnitrosoguanidine (ENNG); serum folate levels decreased during the development of gastric cancer in humans. A case-control study in Mexico showed that folic acid reduced the incidence of intestinal gastric cancer. Most case-control and prospective sample studies of blood specimens have evaluated dietary intake of micronutrients, and overall, it has been clearly shown that moderate amounts of VitC, vitamin E, and beta-carotene are strong protective factors. Intake of high doses of vitamin E has also been shown to significantly prolong the survival time of patients with gastric cancer. The anti-tumor mechanisms of vitamins are mainly antioxidant, scavenging free radicals, activating the immune system, blocking the action of chemical carcinogens, improving intercellular junctional traffic and participating in the maintenance of DNA methylation status. The anti-tumor mechanism of various vitamins can be summarized as follows: β-C is an antioxidant, which can scavenge free radicals, stimulate the immune system and activate the gap junction traffic through retinol and VA acid, and maintain the normal state of cell differentiation. VE is an antioxidant, enhances immune function, and also reduces nitrosamines, and has been initially demonstrated in recent prospective studies and chemoprevention; vitamin E also prevents malignant transformation or overproliferation of cells before and after genetic mutations; many recent studies have reported no effect of vitamin E in smokers. Folic acid is mainly involved in SAM donor methylation process to maintain m frustrated methylation status, in gene regulation and inhibition of oncogene expression. Although research on the anti-tumor mechanism of vitamins has been conducted for many years, there are still many unclear details, especially the question of whether several vitamins act together or singly, and sometimes the influence of reduced vitamin absorption due to tumorigenesis must be excluded. However, as the level of molecular biology improves, the research work on the mechanism will go deeper to the cellular and even molecular level, and its clinical application will be gradually improved. (v) Fruits and vegetables It is now widely believed that long-term consumption of fresh fruits, especially citrus and raw vegetables, has a protective effect and can significantly reduce the occurrence of gastric cancer. In addition, some special varieties of vegetables used in salads also have protective effects, such as: tomatoes, lettuce, cucumbers, carrots, celery, sweet pepper, onions. Local specialty onion vegetables and onions have been shown to be negatively associated with the development of gastric cancer in China and some countries. Both case-control and cohort survey data show that the amount of fresh vegetables and fruits is significantly and negatively associated with gastric cancer mortality. In the United States since 1930 and in Japan since 1950, an increase in fruit and vegetable consumption was followed by a significant decrease in gastric cancer mortality observed. The reason for the reduction of gastric cancer occurrence by consuming large amounts of fresh vegetables and fruits is, on the one hand, the low amount of carcinogens in fresh vegetables and, on the other hand, probably the high amount of vitamins A, C and E contained in them. Depending on the source of vitamin A, it can be divided into plant-based (carotenoids) and animal-based (retinol). 1988 Byers observed that plant-based vitamin A has a stronger anti-cancer effect. Vitamin A differentiates epithelial cells into specific tissues, causes squamous cell carcinoma and other cellular carcinomas in humans to subside, and stimulates the anti-tumor immune system to prevent the development of gastric cancer. The mechanism of action of vitamin C is to inhibit the synthesis of endogenous nitrosamines and the conversion of tissue cells to carcinogenic compounds, and it can even reverse the converted cells to produce anti-cancer effects. The anti-tumor effect of vitamin E has three aspects: ① inhibit the formation of carcinogenic nitrosamines in vivo; ② certain carcinogens can form free radicals in the body, vitamin E can inhibit the formation of free radicals and protect the normal differentiation of cells; ③ enhance the immune function of the body. (6) Soybean products and milk A large number of epidemiological investigation data at home and abroad show that milk, soybean products, fresh fish, fresh meat and eggs have protective effects on gastric cancer mucosa, and beans contain a variety of protease inhibitors, unsaturated fatty acids and phenolic compounds, which have inhibitory effects on carcinogenic processes and nitrosamine formation. American scholars have recently found from animal experiments that crude protease in legumes has a good anti-cancer effect. The relative risk of stomach cancer was reduced to 1/5 if milk was consumed with meat and green vegetables. Milk is rich in calcium and vitamin A, as well as protein colloids, which have a protective effect on the gastric mucosa against toxic substances. Dietary proteins may affect the activity of certain enzymes and thus play an important role in modifying carcinogens.