Dietary prevention of gastrointestinal cancer : epidemiologic studies of fruit, vegetables and cereals

The widely accepted inverse associations between fruit, vegetables, dietary fiber and colorectal cancer risk, have recently been called into question. In addition, dietary studies of certain cancers, such as adenocarcinomas of the esophagus and gastric cardia, and prospective cohort studies of stomach cancer, remain scarce. To study cancers of the esophagus, gastroesophageal junction (cardia), stomach, colon and rectum in relation to diet, we analyzed data from three large studies in Sweden: a nation-wide case-control study of cancers of the esophagus and gastric cardia, a nationwide cohort of Swedish twins, and a population-based prospective cohort study of women living in two counties in Central Sweden. We found fruit, vegetables and antioxidants to be inversely related with all of the studied cancers except gastric cardia cancer. For esophageal and cardia cancers, the absolute risk is so low that tens of thousands of people in the highest risk strata of age and sex would need to increase their consumption in order to prevent one case per year. In relation to stomach cancer, our data hint that individuals with very low consumption of fruit and vegetables were at especially high risk. In relation to colorectal cancer, the inverse association was limited to those who consumed very low amounts of fruit and vegetables (less than 2 servings per day). Cereal fiber intake showed an inverse association only with cancer risk only in the gastric cardia. Intake of fiber from fruit or vegetables, on the other hand, was unrelated to cardia cancer risk. We can speculate that nitrosamine-scavenging mechanisms of cereal fiber may be more important in the gastric cardia than elsewhere in the gastrointestinal tract, in turn due to a suggested higher production of nitrosamines in the proximal stomach. While intervention efforts to prevent certain cancer through dietary changes may not be cost effective (such as in the prevention of the rare esophageal cancers), the overall benefit to health, including the prevention of digestive tract cancers, warrants continued efforts to inform and influence the public regarding adequate consumption of these foods