More Fiber, Less Fat Help Prevent Ovarian Cancer

The women received 18 diet-support group sessions in the first year to help keep them on track and then quarterly maintenance meetings during the following years.

The researchers then monitored the women's rates of ovarian and/or endometrial malignancies over the next 8 years.

The result: Rates of ovarian cancer were roughly similar for women during the first 4 years of the study, whether they were enrolled on the low-fat diet or not. But by the end of more than 8 years of follow-up, a clear trend emerged, with women on the healthier diet having a 40 percent reduction in ovarian cancer incidence.

There was no such effect on the risk of endometrial cancer, however, the researchers added. That was surprising, Morgan said, because some experts theorize that fat increases estrogen levels in the body, which, in turn, may boost risk for both ovarian and endometrial cancer. Previous reports have indicated that low-fat diets lower circulating estrogen, said Morgan, so he expected to see a similar effect for both tumor types.

Women looking to duplicate the diet in their own lives should follow the Food Pyramid guidelines set out by the U.S. Department of Agriculture, Morgan said. But he added that one of the components that made this study so unique was the intense dietary counseling and support the women received over time.

According to Prentice, the diet was developed especially for this research and doesn't follow any contemporary "popular" diets.

"In particular, the Women's Health Initiative intervention did not have a goal of restricting energy [calorie] consumption, though participating intervention group women did lose some weight. Nor was there an attempt to reduce carbohydrates," said Prentice. "On the contrary, most of the reduced dietary fat was replaced by complex carbohydrates."

The potential link between dietary fat and cancer is not fully understood, he added. During the study, Prentice said the researchers did note lower levels of estradiol -- an estrogen hormone produced by the ovaries -- in the blood of dieting women. Estradiol is an important risk factor for cancer among women, he said.

"This or other circulating hormones could have a stimulatory effect on epithelial [blood vessel] tissue in the ovary or breast, possibly including effects on cells in yet undiagnosed cancers," Prentice explained.

"The evidence for reductions in ovarian and breast cancer is strongest among women whose usual [prior] diet was relatively high in fat (e.g. more than 35 percent of calories) who made a comparatively large fat reduction if assigned to the low-fat diet group," he added.

There is an increasing amount of evidence linking healthier diets and exercise to lower cancer risk. But Prentice said he would like to see more basic-science research focused on the ways in which these lifestyle changes affect the biochemical mechanisms that drive cancer.

More information

For more about the USDA's dietary guidelines, visit MyPyramid.

SOURCES: Ross Prentice, Ph.D., professor, biostatistics, University of Washington School of Public Health and Fred Hutchinson Cancer Research Center, Seattle, and principal investigator, Women's Health InitiativeClinical Coordinating Center; Robert Morgan Jr., M.D., section head, medical gynecologic oncology, City of Hope Cancer Center, Duarte, Calif.; Oct. 9, 2007, online edition,Journal of the National Cancer Institute