Older women who stick to a low-fat, high-fiber diet could cut their odds for deadly ovarian cancer, new research shows. In fact, postmenopausal women who stayed on the regimen for more than eight years reduced their risk for the disease by 40%, a US team said. Those who saw the greatest benefit from switching to a low-fat diet were women who had originally eaten a relatively high-fat diet, the researchers added.
On average, the women had managed to add one serving of fruits or vegetables to their daily diet by the end of the six-year follow-up. They had also reduced their daily fat consumption by about 8%.
Background
Ovarian cancer is the fifth leading cancer killer of women. Some 20,000 women in the United States are diagnosed with the disease every year, and about 15,000 women will die from it during the same time frame.
As with most cancers, a woman's chances of survival are better if the disease is found early, but ovarian tumors are a "stealth killer," because they are notoriously difficult to detect in their early stages.
Ross Prentice, PhD, of the Fred Hutchinson Cancer Research Center in Seattle led the new multi-center study. Prior to the publication of this analysis, the impact of particular diets on ovarian cancer was unknown.
The Study
Dr. Prentice's team recruited nearly 50,000 postmenopausal women between the ages of 50 and 79. Nearly 20,000 of those women were randomly assigned to eat a low-fat diet in which fat intake totaled less than 20% of daily calories. They also ate at least five servings of fruits and vegetables a day and at least six servings of whole grains.
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 eight years.
Results
Rates of ovarian cancer were roughly similar for women during the first four years of the study, whether they were enrolled in the low-fat diet or not. But after more than eight years of follow-up, a clear trend emerged, with women on the healthier diet having a 40% reduction in ovarian cancer incidence.
There was no such effect on the risk of endometrial cancer, however, the researchers added. That was surprising, said Robert Morgan, MD, section head of medical gynecologic Oncology at City of Hope Cancer Center in Duarte, California, 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, who was not involved in the study, so he expected to see a similar effect for both tumor types.
Theory
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.
Dietary Guidelines
Women looking to duplicate the diet in their own lives should follow the Food Pyramid guidelines set out by the US 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. The findings support "the idea that lifestyle changes can be made with intensive help," Morgan said.
"Restricting calorie consumption was not a goal, according to Prentice, "though participating intervention group women did lose some weight," he added. "Nor was there an attempt to reduce carbohydrates," said Prentice. "On the contrary, most of the reduced dietary fat was replaced by complex carbohydrates."
