Fiber as protective factor for colon polyps

Abstract

Colorectal cancer is the third leading cause of death in the United States. The change in incidence patterns observed in populations previously considered being at low risk for this disease suggests that environmental factors, including those related to diet contributes to the etiology of colorectal cancer. It has been documented that the majority of colorectal cancer arise in adenomatous polyps. Although the great majority of colon polyps are harmless, some may turn cancerous over time and as many as 30 to 40 percent of middle-age and older adults may have one or more colon polyps. It is estimated that as much as one third to one half of colon cancer risk and one fourth to one third of distal colon adenoma risk might be avoidable by modification of dietary and life-style habits. Factors that have shown the most consistent protective effect against adenomas in epidemiologic studies include, among others, dietary fiber contained in fruits, vegetables and grains. Because colonic polyps are so common in the industrialized world, prevention should play an important role. This is a cohort study to compare the association between fiber intake from fruits, vegetables and grains and the risk of physician diagnosed colon polyps among 2,818 non-Hispanic white cohort members who had undergone colonoscopy. Subjects participated in two cohort studies, the Adventist Health Study-1 (AHS-1) in 1976 and again in the Adventist Health Study-2 (AHS-2) in 2002-2005. Dietary information was obtained from the self-administered questionnaire from the AHS-1, while the outcome was assessed from the AHS-2. Logistic regression analysis was used to estimate the period risk of incident cases of polyps with adjustment for age, gender, BMI, physical activity, alcohol and meat intake. 441 incident cases of colon polyps were identified. After adjusting for age, sex, BMI, physical activity, alcohol and meat, total fiber intake was inversely associated with the risk of colon polyps (RR for highest tertile vs. lowest tertile = 0.706, 95%CI 0.506-0.986; P value= 0.04 and RR for mid tertile vs. lowest tertile = 0.808; 95%CI 0.588 - 1.112; P value= 0.19). This association showed a dose-response effect (P-value for trend= 0.0148). Analyses of various foods, showed that a protective effect of fiber contained in vegetables (RR for highest quartile vs. lowest quartile = 0.662, 95%CI 0.459 - 0.956; P value= 0.0277). Individuals with 1-<4 times/week vs. >4time/week of consumption of meat had an inverse association with colon polyps (RR= 0.592 95%CI 0.406-0.862; P value= 0.006). In this population with a high proportion of lacto-ovo-vegetarians, individuals who consume low amounts of fiber, especially fiber contained in vegetables, and high amounts of meat have higher risk of developing colon polyps. This relationship seems to have a dose-effect response.