The finding, from one the world's largest studies, of over 88,000 women, will send shockwaves through the medical and dietary communities. The Cancer Research Campaign, one of Britain's largest cancer charities, last year joined forces with Kellogs, makers of All-Bran, to promote high-fibre breakfast cereals in a deal worth pounds 1m over three years.
The lack of fibre in the average Western diet - which is low in vegetables, cereals and fruit - has been thought to be the key to many of the chronic diseases of modern living. Now experts suggest that the presence of sugar rather than the absence of fibre in the diet may account for the high incidence of bowel cancer.
The study, published in the New England Journal of Medicine was conducted by a team led by Charles Fuchs at Harvard Medical School and Brigham and Women's Hospital in Boston, Massachusetts. The researchers used as their subjects women enrolled in the huge nurses' health study which began in the mid-1970s and followed them for 16 years from 1980. Separate research is being conducted on cancer incidence among male doctors in the physicians' health study.
The women, who had no history of cancer or bowel disease at the start of the study, gave details of their diet in a questionnaire. By 1996, 787 had developed bowel cancer and 1,012 had adenomas - non-cancerous growths on the gut wall. But, to the researchers' surprise, no link was found between cancer and consumption of fibre.
For at least three decades, dietary fibre has been thought to act as a kind of colonic broom, sweeping food through the gut more quickly and diluting toxic chemicals that build up there. The main evidence was that bowel cancer was almost unknown in Africa, where vegetables and grains are the staple diet
However, epidemiological studies of the link have been "inconclusive", according to the authors, and the findings cast doubt on whether it exists. But they add that there are other good reasons for eating more fibre because it protects against heart disease.
In an accompanying editorial, Dr John Potter of the Fred Hutchinson Cancer Research Centre in Seattle, says in the light of the unexpected findings it may be time to re-examine the biology of bowel cancer and seek another culprit.
"Is it really a surfeit of sugar, not an absence of fibre, that causes the risk of colorectal cancer to increase? Somewhat ignored, sugar consumption is consistently associated with the risk of colorectal cancer and in a dose-response fashion."
There are 31,000 cases of bowel cancer a year in the UK and 17,500 deaths. Ministers have pledged to cut the number of deaths in the under-65s by at least a fifth by 2010.
Gordon McVie, director of the Cancer Research Campaign, said: "This is a very important study. It suggests ... different components of fibre may have different effects."Reuse content