In fact, women with the less-common -- and more difficult to treat -- type of breast cancer could lower their risk of death by as much as 66 percent by following a low-fat diet.

Researchers were unsure whether the reduction in dietary fat was directly responsible for the benefit -- or whether it might be attributable to resulting weight loss or increased consumption of fruits and vegetables. Other studies have shown that excess weight, especially in post-menopausal women, raises breast cancer risk.

Results of the research are published in the Journal of the National Cancer Institute; the NCI provided funding for the study.

The findings surprised the investigators, according to Dr. Rowan Chlebowski of the University of California at Los Angeles, who led the study. They had expected that reducing dietary fat would benefit women with both types of breast cancer, he said.

At the study's onset, the average fat consumption of the 2,437 women who participated, 29 percent of their daily calorie intake, was already 10-12 percent lower than the typical American diet. All of the women had surgery followed by chemotherapy to treat their cancers. Those with the hormone-fueled type of cancer also received tamoxifen.

Dieticians counseled 975 members of the study group to cut their fat intake to about 20 percent of their daily calories. The other 1,462 women were advised to maintain their normal dietary practices.

The lower-fat group lost about 5-6 lbs. over the course of the study.

The overall results with respect to the recurrence of cancer showed almost no difference in outcome between the two groups and, the slight difference that was observed could have been attributable to chance.

However, in the subgroup of women whose tumors were not hormone-fueled, there was a marked difference in outcome for women who followed lower-fat diets, which translated into a 66 lower death risk in that group, the researchers reported.