The results of the Women's Health Initiative Dietary Modification Trial, published in the Journal of the National Cancer Institute, found that after four years, women who decreased dietary fat were 40 percent less likely to develop ovarian cancer than women who followed "normal dietary patterns."

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.

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 results suggested a small reduction in overall risk of cancer among the women who ate less fat but this finding wasn't statistically significant.