A comprehensive study challenges the one accepted truism of dietary research since the 1960s that a fiber-rich diet protects against colorectal cancer.
The latest analysis of evidence has shown that while those who consume food with high fibre content such as cereals, vegetables and fruit are somewhat less likely to get colon cancer, fiber-cancer association is weak, and totally disappears when other factors are taken into account.
According to a study published in the Journal of American Medical Association, fibre is one of the greatest dietary
While people who eat the most fiber 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 anchors, first advocated by the British physician Denis Burkitt in the 1960s, who noticed that rates of colon cancer in Africa were low, and put it down to the fiber-rich diet of local people. Ever since, people have been urged to eat their fiber.
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, with people in the top fifth for the fiber 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.
The team did not find support for a linear inverse association between dietary fibre intake and the risk of colorectal cancer, but said a diet high in dietary fibre from whole plant foods has been found to protect against other diseases, such as heart disease and diabetes.
One of the problems has been defining what fibre actually is. Dietary fibres are not usually fibrous, 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 the benefits they may gain.
However, one study excluded from the study is 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.
However, an author of that study said it was impossible to be sure if this was causal or coincidental. 'Is it the fiber that is causing the reduction of the risk, 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.'
Colorectal cancer, or bowel cancer, a cancer occurring anywhere in the colon or rectum, is the third-most common cancer in men and the second-most common in women. Over 90 per cent of patients are over 50. The 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.