NEW RESEARCH FAILS TO FIND LINK BETWEEN DIETARY FAT, BREAST CANCER.

Byline: Gina Kolata The New York Times

A new study has failed to find any relationship between the amount of fat a woman eats and her chances of developing breast cancer.

The study found that even extremely low-fat diets, with fat providing less than 20 percent of total calories, failed to reduce breast cancer risk. A diet that low in fat includes less animal foods than most Americans eat.

The researchers also found no evidence that the predominant type of fat in the diet - whether saturated, monounsaturated or polyunsaturated - affected a woman's risk of breast cancer.

Although there may be a widespread belief or hope that low-fat diets protect against breast cancer, many leading researchers say that they have been skeptical for years about such a link.

Study after study, they said, has failed to find any association, leaving proponents of the fat hypothesis to postulate that perhaps the fat content of the diet needed to be very low, below 20 percent of total calories, or perhaps women had to start eating low-fat diets when they were children.

The new study, being published today in The New England Journal of Medicine, analyzed data pooled from seven studies in four countries.

An international team of epidemiologists, including those who had the most experience investigating the diet-breast cancer hypothesis, reasoned that by combining data from all the studies, which included more than 335,000 women, they would have enough to answer this lingering question about dietary fat in adulthood and breast cancer.

In each of the seven studies, women's diets were ascertained and then the women were followed for up to seven years. Some women developed breast cancer in that period, and so the investigators could determine whether these women had eaten more fat than those who did not develop breast cancer.

The answer, said Dr. David J. Hunter, the study's lead author, was that fat made no difference in breast cancer rates.

"I feel that it is fairly definite that even at less than 20 percent fat, there is no protection against breast cancer," said Hunter, the executive director of the Harvard Center for Cancer Prevention.

"There is no doubt that a diet that is low in red meats and high-fat dairy products and high in fruits and vegetables is beneficial with respect to other diseases," Hunter said. But, he added, the fat hypothesis "has been a dead end and ultimately a distraction" from studies that might explain what predisposes women to breast cancer.

The dietary fat hypothesis was based in large part on studies with laboratory animals and on epidemiological studies that compared breast cancer rates in countries where the diet was high in fat with the rates in countries where dietary fat was low.

For example, said Dr. Regina Ziegler, a nutritional epidemiologist at the National Cancer Institute, the incidence of breast cancer in the United States and other Western countries is about five times higher than it is in Asian countries.

"Fifteen years ago, everyone would have said that dietary fat explains the differential breast cancer rates between countries," Dr. Ziegler said.