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Dietary Bran Fibre Increases Cancer Risk
The tragedy of science is the slaying of a beautiful hypothesis by an ugly fact. T H Huxley
Part 1: Introduction
In years to come, the past couple of decades of the twentieth century may well come to be known as 'The Bran Age'; a time when it seemed that most of the diseases of Western civilisation were being blamed on a lack of fibre in the diet, and we were all being exhorted to eat as much as possible to cure or prevent those diseases. Diseases blamed on a lack of dietary fibre include: intestinal diseases such as cancer of the colon, appendicitis, constipation and irritable bowel syndrome as well as coronary heart disease, diabetes, obesity, deep vein thrombosis, varicose veins, hiatus hernia and gallstones.
What is fibre?
In a nutshell, fibre is that part of a vegetable which passes undigested through the human gastrointestinal tract. The major natural source of fibre is the cellulose that forms plant cell walls but there are a number of other kinds of fibre. The ones that scientists are interested in most are cellulose, hemicellulose, lignin and pectin.
Origins of the recommendations
The belief that regular bowel movement is important for health is very ancient. In 1932 a 'New Health' movement was promoted in which people were urged to include plenty of roughage in their diets and it was hoped then that the prompt passing of stools after each substantial meal would reduce the incidence of intestinal disease. (1) Thirty years later Dr Dennis Burkitt, while working as a doctor in Africa, discovered that there was a much lower incidence of cancer of the colon among rural black Africans than among Europeans and Americans. He attributed this low incidence to their relatively crude diet. (2) The theory was that fibre hastened the passage of the bowel contents thus allowing less time for cancer-inducing agents to form. This, of course, presupposed that food became carcinogenic in the gut and there was no evidence that it did. Neither was there any evidence that moving food through the intestine at a faster rate decreased the risk of cancer.
So the theory was unsubstantiated then by evidence and later it was to be disproved in practice when it was noticed that, when the rural Africans moved into towns and adopted a Western style low fibre diet, they continued to have a low incidence of colon cancer. A pattern which has also continued with the second generation. It should also be noted that the rural Africans' lifestyle is quite different from that of the Western city dweller: their diet is different in that their energy intake is lower and they eat less protein, fat and sugar, but they are also not exposed to so many pollutants, toxins or mental stresses and any of these factors could be responsible for the difference in disease patterns. Other studies have also shown that there are Western communities (the Mormons of Utah, for example) who also enjoy a low incidence of colon cancer but eat a low fibre diet. (3) Nevertheless, the later findings were not publicised, Burkitt's theories caught the attention of the media who are always ready to exploit a good story. They expanded what was at best a very weak hypothesis into the treatment dogma of today which teaches that fibre is a panacea for all manner of illnesses. (4)
But it would be unfair to heap all the blame on the media. Commercial interests were quick to see the potential in the recommendation. Although Burkitt's recommendations were based on vegetable fibre, bran has a far higher fibre content than vegetables and bran was a practically worthless by-product of the milling process which, until then, had been thrown away. Now, virtually overnight, it became a highly priced profit maker. Bran is quite inedible - there is no known enzyme in the human body that can digest it. Nevertheless, backed by Burkitt's fibre hypothesis, commercial interests could now promote it as a valuable food. The late John Yudkin, Professor Emeritus of Nutrition and Dietetics at London University, pointed out that 'perhaps one reason for the wide acceptance of the suggestion that fibre is an important, if not essential, dietary component is that it had the enthusiastic support of commercial interests.' He was writing in particular about the high-bran products, All Bran and Branslim. (5)
Dr Hugh Trowell, another strong advocate of dietary fibre, confirmed this in 1974, saying that 'a serious confusion of thought is produced by referring to the dietary fibre hypothesis as the bran hypothesis, for many Africans do not consume cereal or bran but remain almost free of constipation, irritable bowel syndrome and diverticular disease'. (6)
Bran, very high in fibre, is the tough outer covering of cereal grains. Every civilisation in history has devised methods and implements solely for the purpose of separating bran from the grain so that they would not have to eat it, and even animals in the Third World today, which are fed bran in their food, reject it.
Fruit and vegetables contain quite small amounts of fibre (see Table) so that if a significantly larger amount is to be eaten, this will have a dramatic effect on the volume of food consumed. Thus the advice to increase fibre in the diet, if we are to use 'natural' sources, must involve a substantial change to the diet as a whole. And that is likely to be unpopular or we would be eating it already.
Table: Amounts of Fibre in Typical Foods
|
Fibre
|
||
| Food | g/100g | g/100kcal |
| Apples, raw |
2.0
|
4.3
|
| Beans, haricot, boiled |
7.4
|
8.0
|
| Cabbage, winter, boiled |
2.8
|
18.7
|
| Carrots, young, boiled |
3.0
|
15.0
|
| Potatoes, new, boiled |
2.5
|
2.6
|
| Plums, raw |
2.9
|
8.0
|
References
1.
Arbuthnot Lane W.
New Health for Everyman
. London: Geoffry Bles, 1932: 127.
2.
Burkitt D P,
et al.
Some geographical variations in disease patterns in East and
Central Africa.
E Afr Med J
. 1963; 40: 1.
3.
Lyon JL, Gardner JW,
et al
. Low cancer incidence and mortality in Utah.
Cancer
1977; 39: 2608
4.
Smith J.
Nutrition and The Media.
In MR Turner, ed
. Preventative Nutrition and
Society.
Academic Press 1981
5.
Yudkin J. Food for thought.
Br Med J
1980; 281: 1563.
6.
Trowell H C. Fibre and irritable bowels.
Br Med J
. 1974; 3: 44
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