The BBC's Pallab Ghosh: "Doctors still think that fibre keeps us in good shape"

A 16-year study involving nearly 90,000 people found no evidence that natural fibre in the diet reduces the risk of cancer.

High-fibre diets have been recommended by doctors since the 1970s after scientists noticed that bowel cancer in Africa - where vegetables and grain is the staple diet - was rare.

Bowel cancer kills 17.500 a year in the UK

But US scientists are now claiming that eating more greens, root vegetables and cereals may do little to lessen the risk of getting the disease.

"Women who ate a high-fibre diet were just as likely to develop colon cancer as women who ate a low-fibre diet," said Charles Fuchs, who led the team based at Harvard Medical School and Brigham and Women's Hospital in Boston, Massachusetts. His report was published in the New England Journal of Medicine.

The research studied 90,000 nurses. By 1996, it found that 800 had developed bowel cancer.

There was no significant difference between those who had eaten a high-fibre diet and those who had not.

Some doctors have called for a re-think on pro-fibre campaigns as a result.

But others claim the women studied were not representative of the general population.

Research disputed

Dr John Toy of the Cancer Research Campaign (CRC) said there were "some question marks".

Only women were used in the study when there are differences in the way bowel cancer develops in men and women.

Also, the nurses were likely to have a high interest in health.

The CRC is involved in a cross-European study of 400,000 people of fibre and bowel cancer. The preliminary results should be available in two years.

Dr Toy advised people to continue to eat a fibre-rich diet, saying it also protected against heart disease, diabetes and other bowel disorders.

Dr Sheila Bingham, assistant director of the Dunn Human Nutrition Centre in Cambridge, said the bulk of research indicated that eating fibre did ward off bowel cancer.

She said: "My advice is to follow the Department of Health guidelines which say we need to be eating more fibre in the form of vegetables and whole grain cereal."

Bowel cancer kills 17,500 a year in the UK.