ArticlesDietary fibre in food and protection against colorectal cancer in the European Prospective Investigation into Cancer and Nutrition (EPIC): an observational study
Introduction
Whether dietary fibre (non-starch polysaccharides) lowers the risk of colorectal cancer is debatable. In reports from large prospective studies in the USA, Finland, and Sweden, no protective effects of fibre were seen.1, 2, 3 In addition, results of large intervention trials have shown that supplements of bran, soluble fibre, or vegetables have not reduced recurrence rates of adenomatous colorectal polyps.4, 5, 6 Death rates for colorectal cancer in vegetarians are no different from those in non-vegetarians.7
These findings of no effect have challenged consensus recommendations, drawn from a large body of epidemiological and experimental findings, that population intakes of fibre should be increased to reduce the risk of colorectal cancer.8, 9 However, all prospective studies of diet and cancer have been done in single populations in whom dietary habits are more or less homogeneous, so that the extent of measurement error would have obscured all but very large underlying associations with diet.10, 11 Measurement error can be reduced by studying populations with diverse dietary practices, thus increasing the between-person variance in diet, and enabling measurement error to be kept to a minimum.10 Such was the approach behind the large prospective collaborative project done in ten different European countries, the European Prospective Investigation of Cancer and Nutrition (EPIC).12 Other reports13, 14 have shown the heterogeneity of dietary intakes of foods supplying dietary fibre in this collaborative cohort. For example, there is over a three-fold range in total average population consumption of fruit and vegetables (excluding potatoes) between centres in Sweden and in southern Spain.13, 14
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Participants
The EPIC cohort consists of subcohorts recruited from 22 centres from Denmark, France, Germany, Greece, Italy, the Netherlands, Norway, Spain, Sweden, and the UK, allowing comparisons between regions with very different rates of cancer occurrence and distribution of lifestyle and food habits. We administered food-related questionnaires and lifestyle and personal questionnaires and obtained anthropometric measurements from all participants at the time of enrolment. The methods have been reported
Results
Since 1992, we have obtained 1 939 011 person-years (average 4·5 years) of follow-up. Our study is based on 1065 incident colorectal cancer cases with complete and satisfactory data as described above. Of these, 706 tumours were located in the colon (287 right side, 286 left side, 133 overlapping or unspecified) and 359 in the rectum. Histological confirmation was available for 1035 cases. Table 1 shows numbers of colorectal cancer tumours according to country, age and sex, and
Discussion
Fibre is one of the most important, if controversial, factors thought to prevent colorectal cancer, with well established biological mechanisms underlying the hypothesis. When entering the large bowel, fibre increases stool weight, reduces transit time, dilutes colonic contents, and stimulates bacterial anaerobic fermentation. This process reduces contact between the intestinal contents and mucosa, and leads to production of short-chain fatty acids, acetate, propionate, and butyrate, which
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