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Dietary Fiber Intake and Risk of Colorectal Cancer: A Pooled Analysis of Prospective Cohort Studies.
Park, Yikyung ScD; Hunter, David J. MB, BS; Spiegelman, Donna ScD; Bergkvist, Leif MD; Berrino, Franco MD; van den Brandt, Piet A. PhD; Buring, Julie E. ScD; Colditz, Graham A. MD; Freudenheim, Jo L. PhD; Fuchs, Charles S. MD; Giovannucci, Edward MD; Goldbohm, R. Alexandra PhD; Graham, Saxon PhD; Harnack, Lisa DrPH; Hartman, Anne M. MS; Jacobs, David R. Jr PhD; Kato, Ikuko MD; Krogh, Vittorio MD; Leitzmann, Michael F. MD; McCullough, Marjorie L. ScD; Miller, Anthony B. MB, BCh; Pietinen, Pirjo ScD; Rohan, Thomas E. MB, BS; Schatzkin, Arthur MD; Willett, Walter C. MD; Wolk, Alicja DMSc; Zeleniuch-Jacquotte, Anne MD; Zhang, Shumin M. ScD; Smith-Warner, Stephanie A. PhD
[Article] JAMA. 294(22):2849-2857, December 14, 2005.

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Context: Inconsistent findings from observational studies have continued the controversy over the effects of dietary fiber on colorectal cancer.

Objective: To evaluate the association between dietary fiber intake and risk of colorectal cancer.

Design, Setting, and Participants: From 13 prospective cohort studies included in the Pooling Project of Prospective Studies of Diet and Cancer, 725 628 men and women were followed up for 6 to 20 years across studies. Study- and sex-specific relative risks (RRs) were estimated with the Cox proportional hazards model and were subsequently pooled using a random-effects model.

Main Outcome Measure: Incident colorectal cancer.

Results: During 6 to 20 years of follow-up across studies, 8081 colorectal cancer cases were identified. For comparison of the highest vs lowest study- and sex-specific quintile of dietary fiber intake, a significant inverse association was found in the age-adjusted model (pooled RR = 0.84; 95% confidence interval [CI], 0.77-0.92). However, the association was attenuated and no longer statistically significant after adjusting for other risk factors (pooled multivariate RR = 0.94; 95% CI, 0.86-1.03). In categorical analyses compared with dietary fiber intake of 10 to <15 g/d, the pooled multivariate RR was 1.18 (95% CI, 1.05-1.31) for less than 10 g/d (11% of the overall study population); and RR, 1.00 (95% CI, 0.85-1.17) for 30 or more g/d. Fiber intake from cereals, fruits, and vegetables was not associated with risk of colorectal cancer. The pooled multivariate RRs comparing the highest vs lowest study- and sex-specific quintile of dietary fiber intake were 1.00 (95% CI, 0.90-1.11) for colon cancer and 0.85 (95% CI, 0.72-1.01) for rectal cancer (P for common effects by tumor site = .07).

Conclusions: In this large pooled analysis, dietary fiber intake was inversely associated with risk of colorectal cancer in age-adjusted analyses. However, after accounting for other dietary risk factors, high dietary fiber intake was not associated with a reduced risk of colorectal cancer.