Dietary Fiber Intake and Risk of Colorectal Cancer

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Abstract
Dietary fiber has been hypothesized to reduce the risk of colorectal cancer. Potential mechanisms for a protective effect include dilution of fecal carcinogens and procarcinogens, reduction of transit time of feces through the bowel, production of short chain fatty acids, which promote anticarcinogenic action, and binding of carcinogenic bile acids.1 However, the results of numerous epidemiological studies have been inconsistent. Ecological correlation studies and many case-control studies have found an inverse association between dietary fiber intake and risk of colorectal cancer.2 On the other hand, most prospective cohort studies have found no association between dietary fiber intake and risk of colorectal cancer3-7 or adenomas (precursors of colorectal cancer),8 and randomized clinical trials of dietary fiber supplementation have failed to show reductions in the recurrence of colorectal adenomas.9-12 Recently, the European Prospective Investigation into Cancer and Nutrition (EPIC) study and the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial observed a statistically significant 25% lower risk of colorectal cancer13,14 or adenomas,15 respectively, in the highest quintile of dietary fiber intake compared with the lowest. Because of these discordant results, the debate continues on whether dietary fiber consumption decreases colorectal cancer risk. In this study, we evaluated the association between dietary fiber intake and risk of colorectal cancer by reanalyzing the primary data from 13 prospective cohort studies.