Is the Association with Fiber from Foods in Colorectal Cancer Confounded by Folate Intake?

Abstract

The effect of multivariate adjustment including folate on the strong protective effect of fiber in foods on colorectal cancer risk in the European Prospective Investigation into Cancer and Nutrition was investigated in 1,721 cases identified in the latest follow-up. The inclusion of an additional 656 cases confirmed our previously published results, with a strong and significant reduction in colorectal cancer risk of f9% for each uncalibrated quintile increase in fiber (P linear trend < 0.001) compared with an 8% reduction in our previous report, which had not been adjusted for folate. Inclusion of the other covariates (physical activity, alcohol, smoking, and red and processed meat) confirmed this significant inverse association for colon cancer and strengthened the association with left-sided colon cancer (P < 0.001). After maximum adjustment, the association between fiber and rectal cancer was not significant, as in our previous analysis. The association with fiber from different food sources was analyzed, but again, there were no significance trends after maximum adjustment. (Cancer Epidemiol Biomarkers Prev 2005;14(6):1552 -6)

Dietary Fiber and Risk of Colorectal Cancer in the Japan Collaborative Cohort Study

“…This may be biologically plausible because the rectum is empty most of the time (49), reducing the abovementioned potential risk-reducing effects of fiber. The colon predominance in risk reduction in the present study is in line with some case-control (50) and cohort studies (21,22).…”

“…On the contrary, the European Prospective Investigation into Cancer and Nutrition (EPIC) reported a lower risk of colorectal cancer with higher intake of total fiber (21,22).…”

“…Furthermore, many animal models show different inhibitory effects of various types of fiber on colon tumor development (7)(8)(9). On the contrary, many prospective studies showed no protective effects of fiber (10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20), although a recent international cohort study in Europe has reported an inverse association between fiber intake and colorectal cancer risk (21,22). In addition, increasing fiber intake did not reduce adenoma recurrence in large intervention trials (23)(24)(25).…”

The fibre–folate debate in colo-rectal cancer

“…001 for linear trend; Bingham et al 2005) compared with an 8 % reduction in the previous report. As in the earlier report, the reduction in risk is apparent at the third quintile of fibre intake of approximately 20 g fibre/d compared with 12 g/d.…”

The Epidemiologic Evidence and Potential Biological Mechanisms for a Protective Effect of Dietary Fiber on the Risk of Colorectal Cancer

“…1), which often has hindered their detection in epidemiological studies where confounding, measurement error, and other forms of bias can drown out any underlying signal. Therefore, the relationships between an exposure of interest and disease outcome often only become apparent in very large, well-conducted cohort studies (such as the European Prospective Investigation into Cancer and Nutrition [EPIC]) [13] or meta-analyses of cohort studies. However, even then there may still be insufficient statistical power to observe a significant association (e.g., in the Pooling Project [14]) if the signal to noise ratio is low.…”