Women who eat high-fibre diets are no less likely to develop colorectal cancer than those who eat little fibre, according to a new US study.
The research, conducted by a team form Harvard University and Brigham and Women's Hospital in Boston, tracked the eating habits of more than 88,000 female nurses over 16 years.
The findings were the same no matter what type of fibre the women consumed, whether or not they smoked and whether or not they exercised.
"There has never been any evidence that a high-fibre, low-fat diet protects people against colon cancer," said Dr Diarmuid O'Donoghue, a consultant gastro-enterologist at St Vincent's University Hospital.
"It was always more of a hope because if there was something causing cancer stuck in the colon it would move along more quickly with a high-fibre diet."
The notion that consuming fibre could improve one's chances of avoiding colorectal cancer was first put forward by Dr Denis Burkitt, a British missionary surgeon who studied the differences in diseases between Africans and Westerners.
"You must remember that Dr Burkitt was making epidemiological observations; he was not participating in controlled experiments," said Prof William Kirwan, a consulting surgeon and professor at Cork University Hospital.
"So that evidence has always been circumstantial. But there is good scientific evidence that, for example, feeding a high-fibre diet to patients with diverticulitis favourably alters the dynamics of the colon."
Both Dr O'Donoghue and Prof Kirwan continue to recommend a diet which is high in fibre. They point out that a number of other illnesses can be improved or prevented with such a regimen, including diabetes, haemorrhoids and gallstones.
Both also agree that the importance of fibre in preventing colorectal cancer could once again change.
"Simply because a study has not yet proven that something happens does not mean it's not happening," said Prof Kirwan.