EATING lots of fibre may do little to protect against colon cancer, the latest analysis of evidence has found.

While people who eat the most fibre — in the form of cereals, vegetables and fruit — are slightly less likely to get colon cancer, the association is weak and disappears altogether when other factors are taken into account, according to an international team in the Journal of the American Medical Association. The research undermines one of the greatest of dietary shibboleths, first enunciated by the British physician Denis Burkitt in the 1960s. Working in Africa, he noticed that rates of colon cancer were low, and put it down to the fibre-rich diet of local people.

Ever since, people have been urged to eat their fibre. The latest analysis pools the results of 13 studies of about 750,000 men and women followed for between 6 and 20 years, in which more than 8,000 colon cancers were detected.

At first sight, the results suggest a link. People in the top fifth for the fibre content of their diet were 16 per cent less likely to get colon cancer than those in the lowest fifth. But on further analysis, the link disappears. If other dietary factors such as red meat, milk and alcohol are included, the link between fibre and cancer becomes insignificant.

“We did not find support for a linear inverse association between dietary fibre intake and the risk of colorectal cancer,” the team concluded. But the team said that a diet high in dietary fibre from whole plant foods has been found to protect against other diseases, such as heart disease and diabetes. John Baron, of Dartmouth Medical School, said that one of the problems has been defining what fibre actually is. Dietary fibres are not usually fibrous, he said, and are certainly not just roughage. They are mostly sugars. And whatever else fibres are, they are a highly confounded lifestyle factor. People who eat fibre do a whole lot of other things that may account for whatever benefits they may gain.

So is this the last word on fibre? Not quite.

One study not included in the analysis was the European Prospective Investigation into Cancer and Nutrition (Epic), which found a strong link. The Epic results showed that people in the top 20 per cent for fibre intake, who ate an average of 35g of fibre daily, had the risk of colorectal cancer reduced by 40 per cent, compared to those eating 15g a day.

But one of the authors of that study, Sheila Bingham, said it was impossible to be sure if this was causal or coincidental. She said: “Does the fibre cause the reduction, or is it simply that high fibre intake is the sign of a diet that is high in fruit, vegetables and whole grains? If it is the latter, the lowered risk could actually be due to other substances.”

So, a controversy well into its fourth decade could still have some way to go.

THE RISKS

Risk factors are a diet high in red meat and fat and low in vegetables; lack of exercise; obesity; heavy smoking or drinking; and a family history of the disease

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