October 5, 1996
Fibre may be implicated in colon cancer.
Fibre and Colorectal Cancer
The following year Drs HS Wasan and RA Goodlad of the Imperial CancerResearch Fund showed that bran can increase the risk of colorectal cancers. (14) 'Many carbohydrates', they say, 'can stimulate epithelial-cell proliferation throughout the gastrointestinal tract. They conclude: 'Until individual constituents of fibre have been shown to have, at the very least,a non-detrimental effect in prospective human trials, we urge that restraint should be shown in adding fibre supplements to foods, and that unsubstantiated health claims be restricted. . . . Specific dietary fibre supplements, embraced as nutriceuticals or functional foods, are an unknown and potentially damaging way to influence modern dietary habits of the general population.'
Various. Fibre and colorectal cancer. Lancet 1996; 348: 956-9.
Fibre and colorectal cancer SIR—It is salutary to be reminded of the limitations of our knowledge of risk factors in health and disease. As Wasan and Goodlad maintain (Aug 3, p 319),1 assertions that up to two-thirds of the variation in incidence of colon cancer is attributable to differences in total fibre and fat consumptions are obviously erroneous. Account must be taken of the wide differences in rates found in Europe and of the enormous differences in incidence rates in adjacent districts, as in Scotland. In Japan, the mortality rate for colon cancer is falling, whereas, from knowledge of risk factors, it should be rising.2 In rural Africans in South Africa, appendicitis, diverticular disease, and colon cancer are near absent.3 Puzzlingly, these diseases are also rare in urban dwellers, despite considerable increases in the intakes of energy and fat and falls in dietary fibre. Equally puzzling, the self-same dietary changes have evoked huge increases in dental caries, obesity in women, hypertension, and diabetes. The authors urge, pragmatically, that for the prevention of colon cancer and other degenerative diseases, “we should continue to follow the general guidelines . . . to eat a diet with more fruit and vegetables and less fat”. Although these recommendations have been urged with evangelical fervour for 20 years, responses have been slight. In the USA energy from fat has fallen from 40% to about 35%, and in the UK the decrease has been even less. In both countries intakes of vegetables and fruit have not risen significantly and the proportion complying with full recommendations is small. The likelihood of increasing intakes of other plant foods (eg, bread or legumes) looks remote too. Since people cannot—or, rather, will not—change their diet, what about fibre supplements, fibre additions to foods, and antioxidant vitamins and minerals? Unfortunately, as Wasan and Goodlad note, benefits resulting from such additions have been mixed; moreover nutritional authorities stress that some of the benefits from plant foods consumption may arise from the fact that they contain additional, not-yet-identified health-promoting constituents. “Health is not a priority for most people in the course of their daily lives, and only surfaces when health problems emerge. Studies have found little evidence that changes in health related behaviour were a response to formal health messages.”4 Compliance with the requirements, dietary and non-dietary, for lessening the risk for colon cancer seems a forlorn hope, as with breast cancer also.5
A R P Walker, I Segal
*Human Biochemistry Research Unit, Department of Tropical Diseases,
School of Pathology of the University of the Witwatersrand, and the
South African Institute for Medical Research, Johannesburg 2000, South Africa; and Gastroenterology Unit, Baragwanath Hospital and University of the Witwatersrand