Dietary Bran Fibre Increases Cancer Risk

Part 2: Diseases

Irritable bowel syndrome

The claims made for fibre are based on its rapid transit through the gut and, because of this property, bran has been a popular way to manage irritable bowel syndrome (IBS) for since the early 1970s. So, is it effective? The answer appears to be no. A number of placebo controlled studies of bran in IBS have not shown any convincing effect of the fibre on overall symptom patterns. Results of a study from St Bartholomew's Hospital in London, showed clearly that fifty-five percent were made worse compared to only ten percent made better. ⁽⁷⁾ All symptoms of IBS were exacerbated by wheat bran, with bowel disturbance most often adversely affected, followed by distension and pain. The authors conclude: 'The results of this study suggest that the use of bran in IBS should be reconsidered. The study also raises the possibility that excessive consumption of bran in the community may actually be creating patients with IBS by exacerbating mild, non-complaining cases.'

When several independent responses were analysed, the only significant improvements with bran treatment were in constipation; but then a number of people believe, wrongly, that they are constipated if they miss only a day. Some patients found that the added bran in their food induced or exacerbated uncomfortable symptoms of flatulence, distension and abdominal pain. In these cases, reduction in the amount of bran eaten was recommended.

Colon cancer

In addition, there is really no direct evidence that an increase of fibre by itself will prevent or cure any of the other diseases. As far as colon cancer is concerned, Burkitt's theory was questioned with the suggestion that the low cancer rates in rural Africans may be due to their high early death rates from other causes so that they do not reach the age at which cancer peaks in Europeans. ⁽⁸⁾ As Europeans usually develop it in their seventies and the life-expectancy of Burkitt's Africans was only around forty, why was it that this suggestion took so long to arrive at? There is also a growing scepticism in the USA that lack of fibre causes cancer. And some studies have even suggested that a fibre-enhanced diet may increase the risk of colon cancer. ⁽⁹⁾ The idea that people must tolerate an unpalatable bran-rich diet to ward off such diseases is founded on extremely dubious hypotheses.

It had been shown in the mid-1980s that dietary fibre increased the risk of colon cancers. ⁽¹⁰⁾ In 1990 The British Nutrition Foundation admitted that the hypotheses that IBS, diverticulosis and colo-rectal cancer are caused by a deficiency of fibre had not been substantiated, neither have those that fibre might protect against diabetes, obesity and CHD. ⁽¹¹⁾ The Seventh King's Fund Forum on Cancer of The Colon and Rectum agreed: 'The Forum commented that cereal fibre does not offer protection against cancer'. ⁽¹²⁾

Dr M Inoue, et al published in 1995 an investigation of cancers at several colorectal subsites: ascending, transverse, descending, sigmoid, and rectum, within a Japanese hospital environment. They concluded that loose or soft faeces are a significant risk factor for cancer at these sites. ⁽¹³⁾ And bran loosens and softens faeces - that's why it is recommended.

The following year Drs HS Wasan and RA Goodlad of the Imperial Cancer Research 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.'

This study spawned several critical letters. It comes as no surprise that half were from people connected with the breakfast cereal industry. ⁽¹⁵⁾

The results of the largest, long-term trial to date, published in 1999, also suggest that, contrary to popular belief, high dietary fibre intake does not protect against colorectal cancer. ⁽¹⁶⁾ Researchers at Harvard Medical School and the Dana-Farber Cancer Institute, both in Boston, Massachusetts, studied 88,757 women over sixteen years. They say:

'no significant association between fiber intake and the risk of colorectal adenoma was found'. But there was what they call an 'unexpected' finding, in that, according to their data, a high consumption of vegetable-derived fiber was actually 'associated with a significant increase (35%) in the risk of colorectal cancer'. They conclude 'Our data do not support the existence of an important protective effect of dietary fiber against colorectal cancer or adenoma'.

. . . and breast cancer

It has been claimed that elevated fruit and vegetable consumption is associated with a reduced risk of breast cancer. To test this, twenty named researchers at seventeen cancer research centres in the USA, Germany, Netherlands, and Sweden examined the association between breast cancer and total and specific fruit and vegetable group intakes. Their studies included 7,377 incident invasive breast cancer cases occurring among 351,825 women. They found no association for green leafy vegetables, 8 botanical groups, and 17 specific fruits and vegetables and conclude:

"These results suggest that fruit and vegetable consumption during adulthood is not significantly associated with reduced breast cancer risk". ⁽¹⁷⁾

Clearly there are two sides to this debate and claims of benefit are by no means proven. That, of course, does not stop a variety of commercial interests from jumping on a very lucrative bran-wagon.

When the American Heart Association published its dietary recommendations in 1982, the US National Cancer Institute (NCI) and Kellogg's got together to promote All Bran. ⁽¹⁸⁾ But by making such health claims, Kellogg's effectively turned All Bran from a food into a drug - and drugs must be approved by the Food and Drugs Administration (FDA). This gave the FDA a problem as the NCI had already given its blessing to All-Bran. They have an even bigger problem now as these later studies, by and large, do not support the claims that fibre has a protective role in cancer.

References

8. Moore T. Dietary fibre: food or fetish? Lancet 1986 i: 1040.
9. Kritchevsky D. Fibre and cancer . in G V Vahouny and D Kritchevsky eds. Dietary Fibre: Basic and Clinical Aspects Plenum, NY. 1986. p427.
10. Dietary studies of cancer of the large bowel in the animal model . In Vahouny GV, Kritchevsky D (Eds). Dietary Fibre: Basic and Clinical Aspects . Plenum, New York. 1986. p 469
11. Complex Carbohydrates in Foods: the Report of the British Nutrition Foundation's Task Force. The British Nutrition Foundation. Chapman & Hall, 1990.
12. Cancer of The Colon and Rectum: the Seventh King's Fund Forum. London: King's Fund Centre, 1990.
13. Inoue M, et al . Subsite-specific risk factors for colorectal cancer: a hospital-based case-control study in Japan. Cancer Causes and Control 1995; 6: 14-22.
14. Wasan HS, Goodlad RA. Fibre-supplemented foods may damage your health. Lancet 1996; 348: 319-20.
15. Various. Fibre and colorectal cancer. Lancet 1996; 348: 956-9.
16. Fuchs CS, et al . Dietary Fiber and the Risk of Colorectal Cancer and Adenoma in Women. New Engl J Med 1999; 340: 169-176, 223-224.
17. Smith-Warner SA, et al. Intake of Fruits and Vegetables and Risk of Breast Cancer: A Pooled Analysis of Cohort Studies. JAMA . 2001; 285: 769-776.
18. Marshall E. Diet Advice, with a Grain of Salt and a Large Helping of Pepper. Science . 1986; 231: 537.