To the immense disappointment of cancer experts, a study of more than 89,000 women has found no evidence that a diet low in fat or high in fiber protects against breast cancer.
For years, investigators have suggested that women with diets high in fat and low in fiber might be more likely to develop breast cancer. Many women say that the first thing they do after being treated for breast cancer is to reduce fat in their diets to protect against a recurrence.
The new study, by Dr. Walter C. Willett of the Brigham and Women's Hospital in Boston and his colleagues, is not the first to fail to find a relationship between diet and breast cancer.
But it is the largest by far and, because it is generally acknowledged to have been well designed and carried out, it offers what many experts view as the most convincing evidence yet that dietary fat and fiber do not contribute to the disease.
"This is an excellent study," said Dr. Marc Lippman, a breast cancer specialist who directs the Vincent Lombardi Cancer Center at Georgetown University. "A lot of people who look at it will wind up saying, 'If your goal is to do something really substantial about breast cancer risk, you're wasting your time with fat reduction.' "
Dr. Daniel Nixon, vice president for professional education at the American Cancer Society, said, "It's certainly disappointing."
But some investigators say they have not given up on the fat and fiber hypothesis.
Dr. Lawrence Kushi of the University of Minnesota, whose own study of 35,000 Iowa women found a similar negative result, said: "I continue to hope. I believe in the back of my mind that we will design a study that will detect a relationship."
Barbara Kronman, a co-director of Share, a New York area self-help group for women with breast cancer, said: "I think women will be disappointed and will not really believe it. This is one of the few areas in which we can feel some control over our lives. If this gets taken away from us, we are left with a very fatalistic approach."
In their study, being published today in the Journal of the American Medical Association, Dr. Willett and his colleagues followed 89,494 nurses for eight years, asking detailed questions about their diets and health.
During the study period, 1,439 of the women developed breast cancer. But, the researchers said, no matter how they analyzed and scrutinized the data, they could not find any relationship between what the women ate and their chances of getting breast cancer.
The fifth of the women eating the smallest amount of fat, those for whom it accounted for less than 25 percent of their total calories, were just as likely to get cancer as the fifth of the women eating the most fat, more than 49 percent of their calories. (Since most fiber came from fruits and vegetables, which have little fat, the more fiber the women ate, the less fat they ate.)