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Numerous dietary factors have been implicated as risk factors for gastric cancer. The decline in gastric cancer rates has coincided with the widespread use of refrigeration and the concomitant higher intake of fresh fruits and vegetables and lower intake of pickled and salted foods. Use of refrigeration for more than 10 to 20 years has been associated with a decreased risk of gastric cancer.14 Lower temperatures reduce the rate of bacterial, fungal, and other contaminants of fresh food, as well as the bacterial formation of nitrites. Additionally, high intake of highly preserved foods may be associated with increased gastric cancer risk,64 potentially due to higher contents of salt, nitrates, and polycyclic aromatic amines.
Much attention has been given to the effects of high nitrate intake. When nitrates are reduced to nitrite by bacteria or macrophages, they can react with other nitrogenated substances to form N-nitroso compounds that are known mitogens and carcinogens. In rats, N-nitroso compounds have been shown to cause gastric cancer. However, studies trying to link N-nitroso exposure to gastric cancer risk have been inconclusive, perhaps reflecting the fact that nitrate intake does not necessarily correlate with nitrosation levels.65 A Swedish cohort study found a nearly 2-fold increased risk of gastric cancer associated with high dietary nitrate intake.64 However, separate large cohort studies from Europe did not demonstrate an association between nitrate intake and risk of gastric cancer.66,67
Another factor implicated in the development of gastric cancer is a diet high in salt (pickled foods, soy sauce, dried and salted fish and meat). High salt intake has been associated with higher rates of atrophic gastritis in humans and animals in the setting of Helicobacter infection and increases the mutagenicity of nitrosated food in animal models.14,68 High-salt diets are associated with a roughly a 1.5- to 2-fold increased risk of gastric cancer.69 Cohort and case-control studies have also found an increased risk of gastric cancer associated with processed meat intake.64,70 Possible mechanisms include higher bacterial loads, up-regulation of Hp cagA expression, and increased cell proliferation and p21 expression.68,71,72
Epidemiologic studies have had inconsistent findings with regard to fruit and vegetable consumption and risk of gastric cancer.73-76 Other foods or dietary factors that have been implicated as potential risk factors for gastric cancer are high intake of fried food, foods high in fat, high intake of red meat, and aflatoxins.70,77-79 Diets with a high intake of fresh fish and antioxidants may be protective.78,80-82 However, there are insufficient data to make definitive conclusions regarding these factors.