The fibre–folate debate in colo-rectal cancer

Abstract

Intervention and prospective studies showing no effect of fibre in protection against colo-rectal cancer have challenged consensus recommendations that population intakes of fibre should be increased to reduce the risk of colo-rectal cancer. The European Prospective Investigation of Cancer and Nutrition (EPIC) of 519 978 individuals aged 25–70 years is the largest prospective study of diet and cancer to date worldwide. It incorporates ten different European countries in order to increase heterogeneity in dietary habits and calibration procedures to reduce measurement error. Data for 1065 reported cases of colo-rectal cancer were reported in 2003. There was a 40% reduction in risk for the highest quintile v. lowest quintile of fibre in food after calibration. It has been suggested that these effects were a result of confounding by folate and other factors. Although there are a number of hypotheses to explain why folate should be protective in colo-rectal cancer, a meta-analysis has shown that folate in food may be protective but there is no effect of total folate (i.e. food plus supplements). In a further analysis of 1826 cases in EPIC, identified in the latest follow-up, the inclusion of an additional 761 cases has confirmed the previously published results, with a strong and significant reduction in colo-rectal cancer of approximately 9% reduction in risk for each uncalibrated quintile increase in fibre (P<0·001 for linear trend) compared with an 8% reduction in the previous report, which had not been adjusted for folate. Inclusion of the other covariates (physical activity, alcohol, smoking and red and processed meat) with folate has confirmed this significant inverse association for colon cancer and strengthened the association with left-sided colon cancer (P<0·001).