Nutrition and gastrointestinal cancer risk - a study of individual food groups

Abstract

Diet is an important modifiable risk factor in gastrointestinal (GI) cancer prevention. Epidemiological evidence suggest a protective effect of food such as vegetables and fruits, and an increased risk with certain foods of animal origin. However, with a vast array of different nutrients within broad categories of food groups, the precise mechanisms underlying an association have yet to be determined. This warrants a more detailed investigation of individual food types to isolate and identify contributing factors. The purpose of this study is to examine the effects of three commonly consumed food types, (1) cruciferous vegetables, (2) soy, and (3) eggs on GI cancer risk. As the evidence on these foods have been limited and controversial, clarification through meta-analyses and systematic reviews would enable further understanding of potential relationships. Database search was completed with MEDLINE, EMBASE, PubMed and Current Contents Connect with additional cross checking of reference lists. Inclusion criteria depended on the risk factor investigated but general requirements included the use of original data and reporting of an odds ratio or relative risk ratio, and 95% confidence interval. Pooled adjusted odds ratios (ORs) comparing highest and lowest categories of dietary pattern scores were calculated using a random effects model. Subgroup and sensitivity analyses were carried out when warranted to determine the impact of modifying variables. The results of this study identified a decrease in risk of cruciferous vegetable consumption and colon cancer (OR, 0.84; 95% CI: 0.72-0.98), with broccoli having a stronger association (OR, 0.80; 95% CI, 0.65-0.99). Subgroup analysis on genetic polymorphism identified reduction in risk certain genotypes. Dietary isoflavone is associated with a statistically significant risk reduction in GI cancers (OR, 0.73; 95% CI: 0.59-0.92), in particular with colorectal cancers (CRC) (OR 0.76, 95% CI: 0.59-0.98). Eggs is associated with a slight increase in risk (OR, 1.15;95% CI: 1.09-1.22) with a positive dose-response, the OR for an intake of low vs high intake were 1.14 (95% CI: 1.07-1.22; p-value heterogeneity =0.38) and 1.25 (95% CI: 1.14-1.38; p-value heterogeneity =0.25) respectively. In conclusion, this study provides evidence to support a protective effect of cruciferous vegetable and soy consumption, as well as an increased risk with egg consumption on GI cancer development.