Dietary fiber intake and risk of colorectal cancer and incident and recurrent adenoma in the PLCO Cancer Screening Trial

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Introduction

Dietary fiber has been associated with a reduced risk of colorectal cancer. We aimed to examine at which stage in the carcinogenic pathway fiber may act, and which food sources of dietary fiber may be most beneficial against colorectal cancer development.

Methods

Participants were identified from the intervention arm of the Prostate, Lung, Colorectal and Ovarian Cancer Screening Trial. Participants received a dietary questionnaire at baseline and flexible sigmoidoscopy at baseline and again 3 or 5 years after. The colorectal cancer, incident adenoma and recurrent adenoma analyses were based on 57,774, 16,980 and 1667 participants, respectively. Multivariate unconditional logistic regression was used to assess risk of incident and recurrent adenoma, and Cox proportional hazards models were used to assess the risk of colorectal cancer, across categories of dietary fiber intake.

Results

Elevated total dietary fiber intake was associated with a reduced risk of incident distal colorectal adenoma (OR highest v. lowest tertile of intake 0.76, 95%CI: 0.63-0.91, Ptrend=0.003), but not recurrent adenoma (Ptrend =0.67). Although the association was not statistically significant for colorectal cancer overall (HR 0.85, 95%CI: 0.70-1.03, Ptrend=0.10), a reduced risk of distal colon cancer was observed with increased total fiber intake (HR 0.62, 95%CI: 0.41-0.94, Ptrend=0.03). Protective associations were most notable for fiber originating from cereals or fruit.

Conclusion

This large, prospective study suggests that individuals consuming higher intakes of dietary fiber have reduced risks of incident colorectal adenoma and distal colon cancer and fibre’s anti-carcinogenic effects may begin early in colorectal carcinogenesis.