The role of diet in tumor development has been confirmed by studies at different levels of evidence. A review of the relationship between diet and upper GI tract tumors, led by Abnet of the National Cancer Institute, was recently published in the journal Gastroenterology. The risk of esophageal cancer, gastric cancer, and certain precancerous lesions is associated with fruit and vegetable intake, which may vary by site and type of pathology. Systematic evaluation shows that the risk of esophageal cancer and gastric cancer is reduced in those with high intake of fruits and vegetables, and some scholars even suggest that the total daily intake of fruits and vegetables should not be less than 400 g. The effect of fruits and vegetables on gastric cancer may be related to tumor type, site and personal factors. A large prospective study in Europe showed a reduced risk of gastric cancer in people with high fruit and vegetable intake, which 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 esophageal squamous and adenocarcinoma, and in addition to total intake, variety of intake was also an important factor. A European study showed a negative association between fruit and vegetable intake and esophageal squamous carcinoma incidence. The mechanism by which fruits and vegetables reduce the risk of tumorigenesis may lie in preventing the further development of precancerous lesions. A Dutch study showed that the risk of Barrett’s esophagus was lower in men with high vegetable intake, while the risk of Barrett’s esophagus did not change significantly in those who consumed fruits or in women. Red meat and processed meat can increase the risk of GI tumors, a belief that is generally confirmed in colorectal cancer. Heterocyclic amines, nitroso complexes, polycyclic aromatic hydrocarbons and high ferrous hemoglobin in red meat from certain cooking methods are 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 for 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 can reduce nitrosamine levels, which is a carcinogen for some tumors. In addition, diet can rapidly and significantly alter the colonic flora and affect the whole organism, such as the metabolites formed by intestinal bacteria after breaking down cholesterol in red meat, which are associated with atherosclerosis formation. As early as 1939, WL Waston et al. reviewed the clinical data of 771 patients with esophageal cancer and concluded that esophageal cancer might be related to the effect of long-term heat stimulation. Since then, scholars have conducted a large number of clinical and epidemiological studies, and what has gained public publication is that maté tea is associated with the occurrence of esophageal squamous carcinoma, while the relationship between hot tea and esophageal squamous carcinoma is unclear. Few studies have shown that coffee increases the risk of esophageal cancer; rather, recent studies have shown a protective effect of coffee. Although several studies have shown that hot tea increases the risk of esophageal cancer, others have shown no association or a protective effect of hot tea, and perhaps only heavy consumption of particularly hot tea increases the risk of esophageal cancer. The reason for the mixed results in the relevant studies may be related to the heterogeneity of the specific ingredients of tea and coffee. Maté tea contains a large amount of polycyclic aromatic hydrocarbons and thus may have a carcinogenic effect. In contrast, tea polyphenols contained in green tea have been shown to inhibit proliferation, anti-angiogenesis, promote apoptosis, and enhance immunity, however, this has 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 promoted hypothesis is that coffee helps prevent liver cancer. There are difficulties in promoting the intake of fruits and vegetables for all people, and some scholars have studied the main components of their anti-cancer effects, among which antioxidant micronutrients and fiber are widely preferred. Vitamin C, vitamin E, beta carotene, and selenium can prevent oxidative damage, and theoretically, adding micronutrients to the diet can help prevent tumors. Studies have shown that micronutrient supplementation is beneficial for pregnant women and those with pernicious anemia, but evidence of its 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 associated with the risk of GI tumors, which needs to be further confirmed in prospective controlled studies. Studies in Lin County, China, have shown that supplementation with vitamin E, beta carotene, and selenium in malnourished populations can help reduce the incidence of gastric cancer, and it remains to be studied 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. V. Vitamin D Studies have shown that decreased levels of vitamin D may increase the risk of tumors in the colorectum, pancreas, and other organs. The results of studies relating vitamin D levels to the risk of upper gastrointestinal tumors are mixed. Some studies suggest that high vitamin D levels increase the risk of esophageal squamous carcinoma and may have no effect on gastric cancer, while others suggest that vitamin D levels are not associated with upper gastrointestinal tumorigenesis. A Meta-analysis of 34 studies showed that consumption of pickles increased the risk of esophageal squamous carcinoma 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 increased 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 to avoid pickles or similar preparation methods. Salt The World Cancer Fund/American Institute for Cancer Research believes that salt and salt-baked 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 more directly showed the relationship between salt and gastric cancer: 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, due to the possible increase in the carcinogenic effect of nitrosoguanidine, the destruction of the bicarbonate barrier leading to inflammation and atrophy, and the enhanced carcinogenic effect of Helicobacter pylori. Coffee Coffee is a popular beverage, despite the existence of insomnia, anxiety, heartburn, withdrawal syndrome and other side effects, there is still much evidence that it is beneficial to chronic diseases such as gastrointestinal tumors. Studies have shown that coffee is negatively associated with the development of colorectal and esophageal cancers, but not with gastric cancer. A recent Meta-analysis showed that coffee reduces the risk of liver cancer and that it has a beneficial effect on cirrhosis, liver enzyme levels, fatty liver, and hepatitis C. These findings are interesting, but the anti-cancer mechanism and the main anti-cancer components of coffee are still worth exploring. Coffee can reduce hepatocarcinogenesis by affecting the immune system and important immune signaling pathways, regulating energy metabolism, and providing micronutrients. Since almost all relevant studies are observational studies, it is difficult to confirm that coffee itself affects the disease process, and randomized studies are needed to confirm this. The relationship between alcohol and tumor risk is complex, and it is classified as a class 1 carcinogen. Some studies have shown that alcohol consumption is positively associated with the occurrence of breast cancer and may be related to the effects received by estrogen metabolism. Conversely, alcohol consumption reduces the occurrence 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 gastrointestinal tumors is even more intricate. In Western countries, heavy alcohol consumption is associated with the occurrence of esophageal squamous carcinoma, while it seems to be unrelated to esophageal and gastric adenocarcinoma. As for colorectal cancer, there may be an association between the two, but it is weaker than for esophageal squamous carcinoma. There is evidence that the reason for the increased tumor risk of alcohol may be related to the reduced absorption of folic acid. X. Dietary pattern Dietary pattern is also an important influencing factor. The way to assess the dietary pattern is the main component analysis rather than simply exploring something. A US study 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 increased 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 showed that a more health-conscious dietary pattern (mainly consuming fruits and vegetables and non-fried fish) was negatively associated with the occurrence of Barrett’s esophagus, while a Western dietary pattern (fast food, meat) would increase the risk of Barrett’s esophagus. XI. Outlook Diet plays an important role in the development of GI tract tumors, but it is still difficult to give a definite conclusion (except for the relationship between certain meats and colorectal cancer, and the relationship between particularly hot beverages and esophageal cancer), which still needs to be confirmed by prospective observational studies. In addition, research related to dietary pattern analysis is very promising and could lead to a more comprehensive health of the public as opposed to targeting a specific tumor or a certain food and nutrient.