Department of Social Medicine, University of Bristol, Canynge Hall, Whiteladies Road, Bristol BS8 2PR, UK.
Nutritional information seems awash with conflicting and contradictory messages, so it can be comforting to cling to advice that appears constant. One concept on which the nutritional cognoscenti are united is the value of eating a diet rich in fibre.1
This quote from a doctor writing in a British broadsheet newspaper illustrates many of the problems faced by nutritional epidemiologists and health practitioners who try to determine the health damaging and health promoting aspects of a populations diet and provide appropriate dietary advice to its members.1 No doubt this doctor will be frustrated if he reads todays volume of the International Journal of Epidemiology (IJE) in which the findings of a prospective cohort study by Mai et al. suggest that diets rich in dietary fibre are not protective against colorectal cancer.2
Burkitt is credited with first proposing that dietary fibre was protective against colorectal cancer and other gastrointestinal problems including diverticular disease and appendicitis.3,4 However, discussions about the value of white (of low fibre content) and brown (of high fibre content) bread date back to antiquity. Interestingly, Hippocrates, in the 5th century BC, believed white bread to be more nutritious:
Wholemeal bread cleans out the gut and passes through as excrement. White bread is more nutritious as it makes less faeces.5
In England the notion that wholemeal bread was good for health had emerged by the late 1500s, with Peter Stubs writing in 1585
doe we not see the poore man that eateth browne bread healthe fuller, stronger, fayrer complectioned and longer living than the other that faredaintelie every day.6
In 1683 Tyron wrote a book about the value of wholemeal bread, stating that it was the most important way to a long and happy life.7 In the US in 1837 Sylvester Graham wrote on the importance of wholemeal bread as a natural food, and to this day wholemeal bread in the States is known as Graham bread.8 Wholemeal bread, known at that time in England as Graham bread, became popular among the upper classes, for the first time, when Queen Victoria took to eating it in 1847.5
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Evidence from observational studies |
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A number of, largely hospital-based, case-control studies have found that dietary fibre is inversely associated with colorectal cancer,15,16 but the results from nested case-control studies or prospective cohort studies have been inconsistent, though results from three recent large studies, including that presented in todays IJE by Mai et al., show no real benefit (Figure 1).1724 The differences between these studies may be due to the heterogeneous nature of fibre and differences in the ways in which fibre has been measured in different studies. The strong inverse association found in the US health professionals study20 was for cancers occurring within the first 2 years of dietary assessment and it is possible that some individuals who developed cancer already had symptoms at baseline and had adjusted their diets to relieve these. A longer, 6-year follow-up, of the same cohort found that the association was considerably weaker than that reported earlier.21 Although recent studies showing little or no protective effect of dietary fibre2123 have been large and well-conducted, these null results may at least in part be explained by the low overall mean fibre intake in the study populations and regression-dilution bias as discussed above.
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Evidence from randomized controlled trials |
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Mai et al. conclude that although their results suggest that fibre is not protective against bowel cancer the public should still be encouraged to consume a high fibre diet since there is good evidence that it is protective against cardiovascular and other chronic diseases.2 However, if fibre really is protective against heart disease and cancers (the two biggest killers in the Western world) then one would expect it to have an important impact on all-cause mortality. To date randomized trials have found no evidence that dietary fibre confers any shortterm benefit on all-cause mortality (Figure 2).2729 Indeed, a large study on British men post myocardial infarction suggested, if anything, that mortality was higher among those allocated to dietary advice aimed at increasing fibre consumption.27
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Why was fibre thought to protect against colorectal cancer? |
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Epidemiologists are aware of the limitations of ecological studies and the need for individual-based analytical studies to provide good evidence of causation. At the same time, as Burkitt pointed out, and others have recently re-emphasized, explaining population differences in disease occurrences is also important.3,30 African populations today continue to experience lower levels of bowel cancer than Western populations,31 and the question remains as to whether this is due to differences in dietary patterns, and if so, what particular features of the diet are healthy or unhealthy.
Many people believe that the dietary habits adopted by Western societies over the last 150 years make important contributions to colorectal and other cancers, hypertension, diabetes, and coronary heart disease. It has been suggested that humans evolved to consume a Paleolithic diet (high animal protein, high fibre, low refined carbohydrate), and that we are therefore genetically determined to eat diets very different to those of todays Western societies.32 Recent evidence has challenged the idea that Paleolithic diets were high in animal fat and protein but the fibre content is likely to have been high.3335 However, the fibre in Paleolithic diets was certainly of plant origin rather than cereal fibre that has been the major source of dietary fibre in Western and African diets for several hundred years.3335 To this extent the notion that we need to consume a diet closer to our earliest origins is not consistent with Burkitts hypothesis which was based on dietary fibre derived largely from cereals.3,4 The differences in dietary fibre content noted by Burkitt continue to present times. The mean consumption of cereal and starchy foods in Sub-Saharan Africa and South Asia greatly exceed those of Europe, the US, Australia, and New Zealand. However, the consumption of fruit and vegetables is considerably lower in Sub-Saharan Africa and South Asia than it is in Western countries.36 Ecological data does not, therefore, suggest that fibre or other nutrients from fruit and vegetables protect against bowel cancer. Further, large cohort studies, including results from the Breast Cancer Detection and Demonstration Project published elsewhere suggest that fruit and vegetable consumption does not protect against colon cancer.3739
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Conclusions |
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Funding |
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References |
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2 Mai V, Flood A, Peters U, Lacey JV Jr, Schairer C, Schatzkin A. Dietary fibre and risk of colorectal cancer in the Breast Cancer Detection Demonstration Project (BCDDP) follow-up cohort. Int J Epidemiol 2003;32:23439.[CrossRef][ISI][Medline]
3 Burkitt DP. Related disease-related cause? Lancet 1969;ii:122931.[CrossRef]
4 Burkitt DP. Epidemiology of cancer of the colon and rectum. Cancer 1971;28:313.[ISI][Medline]
5 The Royal College of Physicians. Historical perspectives: The fall and rise of dietary fibre. In: The Royal College of Physicians of London. Medical Aspects of Dietary Fibre. Bath: Pitman Medical, 1980, pp. 37.
6 Stubs P. The Anatomie of Abuses. London, 1585. Cited in reference 4.
7 Tyron T. (Philotheos Physiologus). The Way to Health, Long Life and Happiness. London, 1683. Cited in reference 4.
8 Graham S. A Treatise on Bread and Bread Making. Boston, 1837. Cited in reference 4.
9 Department of Health. Nutritional Aspects of the Development of Cancer. Report of the Working Group on Diet and Cancer of the Committee on Medical Aspects of Food and Nutrition Policy. Report on health and social subjects number 48. London: The Stationary Office, 1998.
10 World Cancer Research Fund, American Institute for Cancer Research. Goals for populations, advice for individuals. In: Food, Nutrition and the Prevention of Cancer: A Global Perspective. World Cancer Research Fund, American Institute for Cancer Research: Washington, 1997, pp. 50823.
11 Day NE, McKeown N, Wong MY, Welch A, Bingham S. Epidemiological assessment of diet: a comparison of a 7-day diary with a food frequency questionnaire using urinary markers of nitrogen, potassium and sodium. Int J Epidemiol 2001;30:30917.
12 Willett W. Commentary: Dietary diaries versus food frequency questionnairesa case of undigestible data. Int J Epidemiol 2001; 30:31719.
13 Day NE. Authors response from Nick Day. Int J Epidemiol 2001; 31:69293.[ISI]
14 Willett W. Commentators response from Walter Willett. Int J Epidemiol 2001;31:69495.[ISI]
15 Howe GR, Benito E, Castellato R et al. Dietary intake of fiber and decreased risk of cancers of the colon and rectum: evidence from the combined analysis of 13 case-control studies. J Natl Cancer Inst 1992;84:188796.[Abstract]
16 Kaaks R, Riboli E. Colorectal cancer and intake of dietary fibre. A summary of epidemiological evidence. Eur J Clin Nut 1995;49: S10S17.[ISI][Medline]
17 Hiebrun LK, Nomura A, Hankin JH, Stemmermann GN. Diet and colorectal cancer with special reference to fiber intake. Int J Cancer 1989;44:16.[ISI][Medline]
18 Willett WC, Stampfer MJ, Colditz GA, Rosner BA, Speizer FE. Relation of meat, fat and fibre intake to the risk of colon cancer in a prospective study among women. New Engl J Med 1990; 323:166472.[Abstract]
19 Thun MJ, Calle EE, Namboodiri MM et al. Risk factors for fatal colon cancer in a large prospective study. J Natl Cancer Inst 1992;84: 1491500.[Abstract]
20 Giovannucci E, Stampfer MJ, Colditz G, Rimm EB, Willett WC. Relationship of diet to risk of colorectal adenoma in men. J Natl Cancer Inst 1992;84:9198.[Abstract]
21 Giovannucci E, Rimm EB, Stampfer MJ, Colditz GA, Ascherio A, Willett WC. Intake of fat, meat and fiber in relation to risk of colon cancer in men. Cancer Res 1994;54:239097.[Abstract]
22 Steinmetz KA, Kushi LH, Bostick RM, Folsom AR, Potter JD. Vegetables, fruit, and colon cancer in the Iowa womens Health Study. Am J Epidemiol 1994;139:115.[Abstract]
23 Fuchs CS, Giovannucci EL, Colditz GA et al. Dietary fiber and risk of colorectal cancer and adenoma in women. New Engl J Med 1999; 340:16976.
24 Terry P, Giovannucci EL, Michels KB et al. Fruit, vegetables, dietary fiber, and risk of colorectal cancer. J Natl Cancer Inst 2001;93: 52533.
25 Fehily AM, Vaughan-Williams E, Shiels K et al. The effects of dietary advice on nutrient intakes: evidence from the diet and reinfarction trial (DART). J Hum Nutr Dietetics 1989;2:22535.
26 Asano T, McLeod RS. Dietary fibre for the prevention of colorectal adenomas and carcinomas (Cochrane Review). In: The Cochrane Library, Issue 3, 2002. Oxford: Update Software.
27 Burr ML, Gilbert JF, Holliday RM et al. Effects of changes in fat, fish, and fibre intakes on death and myocardial reinfarction: diet and reinfarction trial (DART). Lancet 1989;ii:75761.
28 Alberts DS, Martinez ME, Roe DJ et al. Lack of effect of a high-fiber cereal supplement on the recurrence of colorectal adenomas. New Engl J Med 2000;342:115662.
29 Bonithon-Kopp C, Kronborg O, Giacosa A, Rath U, Faivre J. Calcium and fibre supplementation in prevention of colorectal adenoma recurrence: a randomised intervention trial. Lancet 2000; 356:130005.[CrossRef][ISI][Medline]
30 Leon DA. Commentary on Disease trends in women living in established market economies: evidence of cohort effects during the epidemiological transition. In: Kuh D, Hardy R (eds). A Life Course Approach to Womens Health. Oxford: Oxford University Press, 2002.
31 World Cancer Research Fund, American Institute for Cancer Research. Colon, rectum. In: Food, Nutrition and the Prevention of Cancer: A Global Perspective. World Cancer Research Fund, American Institute for Cancer Research: Washington, 1997, pp. 21652.
32 Eaton SB, Konner M. Paleolithic nutrition. A consideration of its nature and current implications. New Engl J Med 1985;312:28389.[ISI][Medline]
33 Nestle M. Paleolithic diets: a sceptical view. British Nutrition Foundation Nutrition Bulletin 2000;25:4347.
34 Lee RB, DeVore I. Kalahari Hunter-Gatherers: Studies of the !Kung San and Their Neighbors. Cambridge MS: Havard University Press, 1976.
35 Mitton K. Hunter-gatherer dietsa different perspective. Am J Clin Nutr 2000;71:66567.
36 World Cancer Research Fund, American Institute for Cancer Research. Patterns of Diet and Cancer. In: Food, Nutrition and the Prevention of Cancer: A Global Perspective. World Cancer Research Fund, American Institute for Cancer Research: Washington, 1997, pp. 2254.
37 Flood A, Velie EM, Chaterjee N et al. Fruit and vegetable intakes and the risk of colorectal cancer in the Breast Cancer Detection Demonstration Project follow-up cohort. Am J Clin Nutr 2002; 75:93643.
38 Michels KB, Giovannucci E, Joshipura KJ et al. A prospective study of fruit and vegetable consumption and incidence of colon and rectal cancers. J Natl Cancer Inst 2000;92:174052.
39 Voorrips LE, Goldbohm RA, van Poppel G et al. Vegetable and fruit consumption and risk of colon cancer in a prospective cohort study. Am J Epidemiol 2000;152:108192.