More Fiber, Less Fat Help Prevent Ovarian Cancer
Older women who stick to a low-fat, high-fiber diet could cut their odds for deadly ovarian cancer, new research shows.
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In fact, postmenopausal women who stayed on the regimen for more than eight years reduced their risk for the disease by 40 percent, a U.S. team said. Those who saw the greatest benefit from the 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 end of the six-year follow-up. They had also reduced their daily fat consumption by about 8 percent.
The findings support « the idea that lifestyle changes can be made with intensive help, » said Dr. Robert Morgan, section head of medical gynecologic oncology, City of Hope Cancer Center, Duarte, Calif. He was not involved in the study.
Morgan noted that many of his patients ask him about ways they can reduce their cancer risk through diet and exercise. But he said he’s found that « it’s difficult to change habits, especially if they are longstanding. »
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.
According to Morgan, women have a 2 percent risk of getting ovarian cancer over their lifetime, so the relatively small benefit effect shown over the course of this study should be magnified over a lifetime. Besides helping curb cancer, such a diet would also be beneficial in reducing the risk of other chronic diseases, such as heart disease.
The new multi-center study was led by Dr. Ross Prentice of the Fred Hutchinson Cancer Research Center, in Seattle, and published in the Oct. 9 online issue of the Journal of the National Cancer Institute.
The findings come on the heels of a similar study released by the same group in April. That study found that increased consumption of fruits and vegetables helps reduce the risk of head and neck cancers.
The same team has also shown that low-fat diets cut the odds of breast and colorectal cancers. Prior to the publication of this analysis, the impact of particular diets on ovarian cancer was unknown.
In the study, Prentice’s team recruited almost 50,000 postmenopausal women between 50 and 79 years old. Almost 20,000 of those women were randomly assigned to eat a low-fat diet in which fat intake totaled less than 20 percent of daily calories. They also ate at least 5 servings of fruits and vegetables a day and at least 6 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 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.