A diet low in fat could reduce the risk of ovarian cancer in healthy postmenopausal women, according to new results from the Women’s Health Initiative ( WHI ) Dietary Modification Trial.
Researchers found that after four years, women who decreased the amount of dietary fat they consumed were 40 percent less likely to develop ovarian cancer than women who followed normal dietary patterns. As expected, no effect was found during the first four years because preventive benefits on cancer often take many years to develop.

Ovarian cancer affects about 1 in 60 U.S. women in their lifetimes and has the highest mortality of all cancers of the female reproductive system.

The WHI Dietary Modification clinical trial followed 48,835 healthy, postmenopausal women for an average of 8.1 years to test whether a low-fat diet would reduce the risk of cancer and cardiovascular disease.
Nearly 20,000 women in the intervention group were counseled to decrease fat intake to 20 percent of calories and to replace calories from fat with calories from vegetables, fruits, and grains.
The control group ( nearly 30,000 women ) received diet-related education materials only.

Women in both groups started with average consumption of more than 35 percent of calories from fat when they joined the study.
By the end of the first year, the low-fat diet group reduced average total fat intakes to 24 percent of calories from fat, about 11 percent less than the women in the usual diet group.
By the end of the study, women in the low-fat diet group averaged 29 percent calories from fat, compared to 37 percent calories from fat in the usual diet group.
The low-fat diet group also increased their consumption of vegetables, fruits, and grains.

Researchers found that women who started with the highest fat intake and who reduced their fat intake the most during the study lowered their risk of ovarian cancer the most.
In addition, although no effect on rates of endometrial cancer were found, the new results suggest a small reduction in overall risk of cancer among the women who ate less fat, but this finding was not statistically significant.

In the study's primary findings published in the 2006, issue of the Journal of the American Medical Association ( JAMA ), women in the low-fat diet group had a tendency toward reduced risk of breast cancer, heart disease, and stroke, and no reduction in risk of colorectal cancer. The overall 9 percent reduction in breast cancer was not statistically significant; however, like the results for ovarian cancer, the study found that women who started with the highest fat intake lowered their risk of breast cancer more markedly.

The WHI is the most comprehensive study to date of the causes and prevention of the major diseases affecting the health of older women. Over 15 years, the study’s findings on heart disease, breast and colorectal cancer, and osteoporosis have stimulated many changes in clinical practice. The WHI is also one of the largest studies of its kind ever undertaken in the United States and is considered a model for future studies of women’s health.

This study of low-fat dietary pattern is one of the three randomized clinical trials that make up the WHI. The others included trials of hormone therapy ( estrogen plus progestin and estrogen alone ). Both trials were stopped early because of increased risk of diseases like stroke, blood clots, and breast cancer, and because the hormones failed to reduce risk of heart disease.
The third clinical trial studied the effects of Calcium and Vitamin D supplementation on osteoporosis-related bone fractures and on colorectal cancer. As reported in 2006, the study found that Calcium and vitamin D supplements provide a modest benefit in preserving bone mass and prevent hip fractures in certain groups of healthy postmenopausal women, especially those over age 60, but do not prevent other types of fractures or colorectal cancer.

Source: National Institutes of Health, 2007

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