Cancer growths 'not prevented by fibre'

Healthy eating alone 'not enough to prevent bowel cancer'

High-fibre diets do not prevent growths which can develop into bowel cancer tumours, say researchers.

The finding goes against previous thinking that high-fibre, low fat diets reduce the risk of colorectal cancer - disease of the large intestine and rectum.

Colorectal adenomas - tumours - which are usually benign but can develop into cancer are not prevented by an increased intake of fibre, say the studies published in the New England Journal of Medicine.

Colorectal cancer can take years to develop, but the adenomas, or polyps, which can develop into tumours appear faster.

"There may be many reasons to eat a diet that is low in fat and high in fibre, but preventing colorectal adenomas - at least for the first three to four years - is not one of them," said Dr Tim Byers of the University of Colorado School of Medicine.

Higher risk

In the first study, Dr Arthur Schatzkin of the National Cancer Institute (NCI) put 958 people on a diet low in fat, high in fibre and high in fruits and vegetables.

Another 947 people were simply given a brochure on healthy eating and told to follow their usual diet.

All 1,905 had already had at least one precancerous polyp removed within the previous six months. That meant they had a higher-than-average risk of colorectal cancer.

After four years, the risk of developing another such polyp was virtually identical in the two groups.

In the second study, led by David Alberts of the Arizona Cancer Centre, 719 people ate half an ounce of wheat bran fibre each day while 584 others consumed less than a tenth of an ounce.

'Disappointing' results

After three years, tests showed the risk of developing another precancerous polyp was virtually the same in the two groups.

The authors said three years may have been too short to see a significant difference in the two groups, but two other major studies, the Nurses' Health Study and the Health Professionals' Follow-up Study, also "failed to find that cereal fibre prevents colon cancer".

Dr Byers said the results are "disappointing."

Studies in other countries have shown that colorectal cancer rates are lower in areas of the world where people eat more fruits and vegetables, and that people from those areas increase their risk of cancer when they adopt a high-fat, low-fibre diet.

The American Institute for Cancer Research, a Washington-based charity that focuses exclusively on the link between diet and cancer, said the latest results from the NCI study "should not prompt people to abandon diets that have been consistently linked to reducing the risk of colon cancer".

Spokeswoman Ritva Butrum said the NCI study may simply show that dietary changes need to be made early in life as the average subject in the NCI test was 61.