STUDY: FIBER NO CANCER BARRIER; 16-YEAR EFFORT AIMED AT EFFECTS ON COLON.

Byline: Sheryl Stolberg The New York Times

It has been nearly three decades since Dr. Denis Burkitt, a British missionary surgeon who studied the differences in diseases between poor Africans and affluent Westerners, postulated that the Africans' high-fiber diet protected them against colon cancer. He spread his thesis as dietary gospel, prompting millions to change their diets.

Now the largest study ever to examine Burkitt's theory has found that, at least when it comes to preventing colon cancer, all those fruits, vegetables and cereals don't do any good.

The research, conducted by a team from Harvard University and Brigham and Women's Hospital in Boston, tracked the eating habits of more than 88,000 female nurses over 16 years and found that women who ate a high-fiber diet were no less likely to develop colo-rectal cancer or polyps, which can be a precursor to cancer, than women who ate little fiber.

The findings were, for the most part, the same no matter what type of fiber the study subjects ate or how fastidious their habits - whether they smoked or did not smoke, whether they dined on fatty steak or lean tofu, whether they exercised regularly or sat on the couch and watched television.

The researchers and others commenting on their findings noted that the study had its limitations. For example, many scientists believe men and women respond differently from each other to dietary fat and fiber, and the study group involved only women. Still, the new study adds to research suggesting that when it comes to colo-rectal cancer, the benefits of fiber have yet to be proved.

``We really can't substantiate a protective effect of fiber on the rates and risk of colon cancer,'' said Dr. Charles Fuchs, a medical oncologist at Brigham and Women's and the lead author of the study, which appears in today's issue of the New England Journal of Medicine.

``That is not to say that fiber is not a good thing,'' Fuchs added. ``It is still helpful, but not for colon cancer.''

Indeed, experts were quick Wednesday to urge Americans to continue to eat a diet rich in fruits, vegetables and whole grains, primarily because those fiber-rich foods protect against the leading killer in the United States, heart disease - a fact widely advertised by cereal makers.

In addition, a high-fiber diet has been shown to prevent other types of cancer, including cancer of the mouth, pharynx, larynx, esophagus and stomach, said Dr. Michael Thun, vice president for epidemiology at the American Cancer Society.

None of these, however, is as common as colo-rectal cancer, which kills more Americans - an estimated 57,000 in 1998 - than any type of cancer except lung cancer.

While experts say the best way to prevent colo-rectal cancer is to undergo regular screening, some interviewed Wednesday were unconvinced by the findings of Fuchs and his colleagues.

They argued that Burkitt's hypothesis might indeed be true but was difficult to prove through a study that relied, as the Boston research did, on participants to accurately recall their own eating habits. They also said other factors, such as consumption of sugar, which has been associated with an increased risk of colon cancer, could have affected the results.

``This is an experienced group. It's a study with a strong design. But it is by no means the last word on the subject,'' said Dr. Arthur Schatzkin, senior investigator in the nutritional epidemiology branch of the National Cancer Institute. ``It is possible that there really is a true relationship between fiber intake and colo-rectal cancer, but it is just that the epidemiologic tools that we use are too crude to see it.''

The final word, Schatzkin said, will come after scientists conduct controlled clinical trials comparing cancer rates in people who eat fiber-rich diets with those of people who do not.

He is conducting one such study: the Polyp Prevention Trial, financed by the cancer institute. It began in 1991 and involves 2,000 people; half have been eating a specially designed high-fiber diet, while the other half have eaten as they normally would. Schatzkin said he is analyzing the results.

The findings in the New England Journal article were drawn from the Nurses' Health Study, which since 1976 has been chronicling the health and habits of 121,700 female registered nurses. The nurses, who were 30 to 55 years old when the study began, were sent detailed questionnaires about their eating habits; the questionnaires were updated every two to four years.