High fibre diet gives little protection against bowel cancer

Dec 14 2005

The once accepted doctrine that a high fibre diet prevents cancer has been challenged by new dietary research.

The latest analysis of evidence has in fact found that eating lots of fibre may do little to protect against colon cancer.

According to an international team, 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.

This new research undermines one of the greatest of dietary beliefs of all times, which originated from the British physician Denis Burkitt in the 1960s, who noticed when working in Africa that the rates of colon cancer were low, and attributed it to the fibre-rich diet of local people.

Since then people have been encouraged to eat more fibre.

However in this latest analysis, which combines the results of 13 studies of around 750,000 men and women.

The participants were monitored for between 6 and 20 years, in which time more than 8,000 colon cancers were detected.

The results initially suggested there was a link, as those 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 as if other dietary factors such as red meat, milk and alcohol are included, the link between fibre and cancer becomes insignificant.

The team concluded there was little support to associate dietary fibre intake and the risk of colorectal cancer.

However they do say 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.

According to John Baron, of Dartmouth Medical School, one of the problems has been defining what fibre actually is.

Barron says dietary fibres are not usually fibrous, and are certainly not just roughage.

They are in fact mostly sugars, and whatever else fibres are, they are a highly confounded lifestyle factor.

He says as a rule the people who eat fibre do a whole lot of other things that may account for whatever benefits they may gain.

This however may not be the definitive word on fibre.

It appears that one study not included in the analysis was the European Prospective Investigation into Cancer and Nutrition (EPIC), which did if fact find 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.

Also, one of the study authors, Sheila Bingham, says it is impossible to be sure if the results were causal or coincidental; 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, she says the lowered risk could actually be due to other substances.

Colorectal cancer, or bowel cancer, is cancer occurring anywhere in the colon or rectum.

It is the third-most common cancer in men and the second-most common in women and the majority of patients are over 50.

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.

The study is published in the Journal of the American Medical Association.