The role of diet in tumor development has been confirmed by studies at different levels of evidence, and a number of scholars, led by Abnet of the National Cancer Institute, have conducted a review of the relationship between diet and upper gastrointestinal tract tumors, published recently in the journal Gastroenterology. Fruits and Vegetables The risk of esophageal and gastric cancers and certain precancerous lesions is associated with the intake of fruits and vegetables, which may vary depending on the site and type of pathology. Systematic evaluations have shown that those with a high intake of fruits and vegetables have a reduced risk of esophageal and gastric cancers, and some scholars even recommend a total daily intake of fruits and vegetables of not less than 400g. The effect of fruits and vegetables on gastric cancer may be related to tumor type, site and individual factors. A large prospective study in Europe showed that the risk of gastric cancer was reduced in people with high fruit and vegetable intake, and was only statistically significant in fresh fruit and gastric cancer, citrus and pancreatic cancer, smoking, and Nordic populations. Similarly, high fruit and vegetable intake reduced the risk of squamous esophageal cancer and adenocarcinoma, and diversity of intake, in addition to total intake, was an important factor. In a European study, the variety of fruits and vegetables consumed was negatively associated with the development of squamous esophageal cancer. The mechanism by which fruits and vegetables reduce the risk of tumorigenesis may lie in preventing the further development of precancerous lesions. A study in the Netherlands showed that the risk of Barrett’s esophagus was lower in men with a high intake of vegetables, whereas the risk of Barrett’s esophagus was not significantly altered in fruit eaters or women. Meat Red meat and processed meats increase the risk of gastrointestinal tumors, an observation that is generally confirmed in colorectal cancer. Heterocyclic amines, nitroso-complexes, polycyclic aromatic hydrocarbons, and high ferrous heme from red meat produced by certain cooking methods have been associated with tumorigenesis. Dietary intake databases (e.g., CHARRED) can provide information on possible carcinogens in meat. Case-control studies have shown that red meat is strongly associated with the risk of esophageal cancer, and cohort studies provide similar but weaker evidence. Studies have also shown that ferrous hemoglobin may be the most direct potential factor in the development of esophageal cancer. Similarly, case-control studies have shown that red meat is associated with the development of gastric cancer, but cohort studies do not support this at this time. Studies suggest that the interaction of different foods with gastrointestinal flora may influence tumorigenesis. Gut bacteria reduce levels of nitrosamines, which are carcinogens in some tumors. In addition, diet can rapidly and dramatically change the colon flora and affect the whole organism, e.g. the metabolites formed by gut bacteria after breaking down cholesterol in red meat are associated with atherosclerosis formation. Hot drinks As early as 1939, WL Waston et al. reviewed the clinical data of 771 cases of esophageal cancer patients and concluded that esophageal cancer may be related to the effect of prolonged thermal stimulation. Since then, scholars have conducted a large number of clinical and epidemiological studies. What has gained public publication is that mate tea is associated with the development of esophageal squamous carcinoma, while the relationship between hot tea and esophageal squamous carcinoma is not clear. Few studies have shown that coffee increases the risk of esophageal cancer; on the contrary, newer studies suggest a protective effect. Although several studies have shown that hot tea increases esophageal cancer risk, other studies have shown no association or a protective effect of hot tea, and perhaps only large amounts of particularly hot tea increase esophageal cancer risk. The reason for the mixed results in related studies may be related to the heterogeneity of the specific components of tea and coffee. Matei tea contains high levels of polycyclic aromatic hydrocarbons and may therefore be carcinogenic. On the contrary, green tea contains tea polyphenols that have been shown to inhibit proliferation, anti-angiogenesis, promote apoptosis, enhance immunity, etc., but have only been confirmed in cell lines or animal models. Some scholars have also studied the relationship between tea, coffee and maté tea and other digestive tract tumors, but the results are difficult to unify, among which the interesting and highly popularized hypothesis is that coffee helps to prevent liver cancer. Micronutrients, antioxidants and multivitamins There are difficulties in promoting the increased intake of fruits and vegetables at the national level. Some scholars have studied the main components of fruits and vegetables that play a role in fighting cancer, and among them, antioxidant micronutrients and fibers are widely favored. Vitamin C, vitamin E, beta carotene and selenium prevent oxidative damage, and the addition of micronutrients to the diet is theorized to help prevent tumors. Studies have shown that the addition of micronutrients is beneficial to pregnant women and those with pernicious anemia, but evidence of their ability to prevent tumors is still lacking. Observational studies have shown that plasma levels of vitamin E, beta carotene, selenium, retinol, and other micronutrients are negatively correlated with the risk of gastrointestinal tumors, which still needs to be further confirmed by prospective controlled studies. The study in Linxian County, China, showed that vitamin E, β-carotene, and selenium supplementation given to malnourished populations helped to reduce gastric carcinogenesis, and it remains to be investigated whether the same effect can be obtained in well-nourished populations. According to current guidelines and consensus opinion, it is not recommended to promote the addition of micronutrients as in the United States, and there is even evidence that the addition of multivitamins may be harmful. Vitamin D Studies have shown that decreased levels of vitamin D may increase the risk of tumors in the colorectum, pancreas, and other organs. Studies correlating vitamin D levels with the risk of developing tumors in the upper gastrointestinal tract have shown mixed results. Some studies suggest that high vitamin D levels will increase the risk of squamous esophageal cancer and may have no effect on gastric cancer, while others suggest that vitamin D levels are not associated with upper gastrointestinal tumorigenesis. Based on the heterogeneity of the available studies, large sample sizes and high-quality studies are needed to discern this dispute. Pickles A Meta-analysis of 34 studies showed that consumption of pickles increased the risk of squamous esophageal cancer by 2-fold, but most of the included studies were retrospective and more prospective studies are needed. Another Meta-analysis of 60 studies also showed that pickles increase the risk of gastric cancer. The key factors in the formation of pickles are bacterial and fungal colonization and fermentation, but the process produces potentially carcinogenic mycotoxins and nitrosamines, so it is recommended that pickles be avoided or similar preparations be avoided. Salt The World Cancer Fund/American Institute of Cancer Research believes that salt and salt-h foods may induce stomach cancer. As early as 1965, Joossens et al. found that salt may be a risk factor for stroke and gastric cancer, and in 1996, a study showed the relationship between salt and gastric cancer more directly: mortality from gastric cancer was associated with 24-hour urinary salt excretion. A Meta-analysis of 10 cohort studies showed an increased risk of gastric cancer in people with high salt intake, which was attributed to the fact that salt may increase the carcinogenic effect of nitrosoguanidine, disrupt the bicarbonate barrier and thus lead to inflammation and atrophy, and enhance the carcinogenic effect of Helicobacter pylori. Coffee Coffee is a popular beverage, and despite side effects such as insomnia, anxiety, heartburn, and withdrawal syndrome, there is still a lot of evidence to suggest that it is beneficial for chronic diseases such as digestive tract tumors. Studies have shown that coffee is negatively associated with the development of colorectal and esophageal cancers, but not with stomach cancer. A recent Meta-analysis showed that coffee reduces the risk of liver cancer, and that it has a favorable effect on cirrhosis, liver enzyme levels, fatty liver, and hepatitis C. The above findings are very interesting, but the anticancer mechanism and the main anticancer components of coffee are still worth exploring. Coffee can reduce hepatocellular carcinoma by affecting the immune system and important immune signaling pathways, regulating energy metabolism, and providing micronutrients. Since almost all studies are observational, it is difficult to confirm that coffee itself affects the disease process, and randomized studies are needed. Alcohol The relationship between alcohol and the risk of tumorigenesis is complex, and it is classified as a class 1 carcinogen. Some studies have shown that alcohol consumption is positively associated with breast cancer development, possibly related to the effects received on estrogen metabolism. In contrast, alcohol consumption reduces the incidence of kidney cancer, possibly due to the diuretic effect of alcohol, which reduces the exposure of the kidneys to carcinogens in the urine. The relationship between alcohol and digestive tract tumors is even more intricate. In Western countries, heavy drinking is associated with the development of esophageal squamous carcinoma, while it does not seem to be associated with esophageal adenocarcinoma and gastric adenocarcinoma. As for colorectal cancer, there may be a link between the two, but it is weaker than for esophageal squamous carcinoma. There is evidence that the reason for the increased risk of tumors from alcohol may be related to decreased folate absorption. Dietary patterns Dietary patterns are also an important influence, and the way to assess dietary patterns is by major component analysis rather than simply exploring something. A study in the United States showed that a fruit- and vegetable-based dietary pattern reduced the risk of esophageal squamous, adenocarcinoma, and gastric adenocarcinoma, while a meat- and nitrate-based dietary pattern would increase the risk of esophageal adenocarcinoma, squamous, and non-cardia gastric adenocarcinoma. Another study examined the relationship between dietary patterns and Barrett’s esophagus in a similar way, and the results showed that a more health-conscious dietary pattern (predominantly fruits and vegetables and non-fried fish) was negatively associated with the development of Barrett’s esophagus, whereas a Western dietary pattern (fast food, meat) increased the risk of Barrett’s esophagus. OUTLOOK Diet plays an important role in gastrointestinal tumorigenesis, but it is difficult to give a definitive conclusion (except for the association between certain meats and colorectal cancer, and the association between particularly hot beverages and esophageal cancer), which still needs to be confirmed by prospective observational studies. In addition, studies related to dietary pattern analysis are very promising and could lead to a more comprehensive health of the public, as opposed to targeting a specific tumor or certain foods and nutrients.