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

Abstract

To examine the association of dietary fiber with the risk of colorectal cancer in a population with a high incidence of cancer and a low fiber intake, we analyzed the data from the Japan Collaborative Cohort Study. From 1988to 1990 men and women aged 40 to 79 years completed a questionnaire on dietary and other factors. Intake of dietary fiber was estimated using a food frequency questionnaire. Rate ratios (RR) were computed by fitting proportional hazards models. During the mean follow-up of 7.6 years, 443 colorectal cancer cases were recorded. In all participants, we found a decreasing trend in risk of colorectal cancer with increasing intake of total dietary fiber; the multivariate-adjusted RRs across quartiles were 1.00, 0.96 [95% confidence interval (95% CI), 0.72-1.27], 0.72 (0.53-0.99), and 0.73 (0.51-1.03; P trend = 0.028). This trend was exclusively detected for colon cancer: the corresponding RRs were 1.00, 0.90 (95% CI, 0.64-1.26), 0.56 (0.38-0.83), and 0.58 (0.38-0.88; P trend = 0.002). The decrease in RRs with increasing intake of dietary fiber was larger in men than in women. No material differences appeared in the strength of associations with the risk between water-soluble and insoluble dietary fiber. For food sources of fiber, bean fiber intake was somewhat inversely correlated with colorectal cancer risk. This prospective study supported potential protective effects of dietary fiber against colorectal cancer, mainly against colon cancer. The role of dietary fiber in the prevention of colorectal cancer seems to remain inconsistent, and further investigations in various populations are warranted. (Cancer Epidemiol Biomarkers Prev 2007;16(4):668 -75)

Intake of dietary fiber, especially from cereal foods, is associated with lower incidence of colon cancer in the HELGA cohort

“…Overall, most of the associations in the present study were found for men, which is congruent with two other studies that differentiated between men and women 28,31 ; the remaining cohort studies that performed sex-specific analyses did not find any overall associations. 8,[15][16][17]24,30 The differences seen between men and women are difficult to explain.…”

“…25 The present study included more cancer cases from updated registries and had a specific Scandinavian focus with particular emphasis on cereal fiber, especially from high fiber cereal foods. Besides the EPIC study, our results are congruent with four other prospective studies 17,28,30,31 and with a recent nested case-control study, nested within seven UK cohort studies, that found that intake of total dietary fiber was inversely associated with colorectal cancer risk (when using data from food diaries). 26 Only two other studies have found results similar to ours with regard to intake of cereal fiber; 25,30 however, neither attempted to subdivide cereal foods into high-and low fiber cereal foods.…”

“…However, some cohort studies indicate a protective role, [25][26][27][28][29][30][31] and possible reasons for these discrepancies could include limited statistical power, low fiber intake or variation in fiber intake, or inadequately detailed data. Furthermore, most studies have investigated colorectal cancer as one disease or did not differentiate between colon cancer subtypes, and only few considered the impact of different fiber sources.…”

Dietary Fibre and the Risk of Colorectal Cancer: a Case-Control Study

“…Inverse associations were observed between soluble fibre and insoluble fibre and colon cancer but not rectal cancer. The results of a Japanese collaborative study are consistent with our findings (Wakai et al, 2007). The reasons may be that rectum is empty in most of the time, thus reducing the effect of fibre (McNeil et al, 1981) or because the fermentable rates of fibre and bacterial growth are highest in the colon (Mai et al, 2003).…”

“…(i) In the large bowel, fibre can increase stool bulk, dilute faecal carcinogens, shorten faecal transit time and reduce the contact of carcinogens with the colon epithelium (Bingham, 1990;Schatzkin, 2000). (ii) Fibre can bind to the bile acid, which can produce carcinogens (Wakai et al, 2007). (iii) Fibre can be fermented by gut flora to short-chain fatty acids.…”