Dietary fibre colon cancer risk link still unclear, says study
by about 40 per cent, but appears to have no significant effects
against rectal cancer, says a new study that highlights the need
for clarification.
"This prospective study supported potential protective effects of dietary fibre against colorectal cancer, mainly against colon cancer," wrote lead author Kenji Wakai from the Aichi Cancer Center Research Institute. The link between colorectal cancer and dietary fibre was first proposed in 1971 by Denis Burkitt (Cancer, Vol. 28, pp. 3-13). The field has been littered with conflicting views ever since. The new study, published in the new issue of Cancer Epidemiology Biomarkers & Prevention, investigated the link between dietary fibre intake, both soluble and insoluble, and the risk of colon and rectal cancer in a population with a high incidence of cancer and a low fibre intake. Almost one million new cases of colorectal cancer are diagnosed every year worldwide, according to the European School of Oncology, with the cancer claiming 492,000 lives annually. Countries such as Japan have seen a rapid increase in the incidence of the cancer, linked to the "westernisation" of the diet. The Japan Collaborative Cohort Study followed 43,115 men and women aged 40 to 79 for an average of 7.6 years, with some 443 cases of colorectal cancer recorded during this time. Dietary assessments were performed using a food frequency questionnaire (FFQ). In all participants, the researchers observed a decreasing trend in colorectal cancer risk with increasing intake of total dietary fibre, with the highest fibre intake associated with a 27 per cent reduction compared to the lowest fibre intake. Further analysis showed that the trend was exclusive for colon cancer, with the highest fibre intake associated with a 42 per cent reduction compared to the lowest fibre intake. No significant differences were observed when the researchers classified the fibre as soluble or insoluble. Fruit and vegetable fibres are soluble, while cereal fibres are typically insoluble. In animal tests insoluble fibres have shown to be protective towards colorectal cancer, but soluble fibre tends to increase the incidence of cancer. In human epidemiological studies the inverse has been reported. "The role of dietary fibre in the prevention of colorectal cancer seems to remain inconsistent, and further investigations in various populations are warranted," concluded the researchers. The study does have several limitations, most notably the use of food frequency questionnaires to measure dietary intakes. Such questionnaires are subject to some error from the participants when required to recall or estimate dietary intakes of certain food items. Additionally, colorectal cancer is known to have a latency period of between 10 and 20 years, with none of the participants diagnosed with the cancer at baseline. Source: Cancer Epidemiology Biomarkers & Prevention April 2007, Volume 16, Number 4, Pages 668-675; doi: 10.1158/1055-9965.EPI-06-0664 "Dietary fiber and risk of colorectal cancer in the Japan Collabortative Cohort Study" Authors: K. Wakai, C. Date, M. Fukui, K. Tamakoshi, Y. Watanabe, N. Hayakawa, M. Kojima, M. Kawado, K. Suzuki, S. Hashimoto, S. Tokudome, K. Ozasa, S. Suzuki, H. Toyoshima, Y. Ito, A. Tamakoshi for the JACC Study Group
