Long-term adherence to a low-fat diet may reduce the risk of ovarian cancer, according to the results of the Women's Health Initiative Dietary Modification trial, which involved nearly 50,000 postmenopausal women.

"While other studies have examined the association between dietary fat and the incidence of cancer, including cancer of the ovary, among postmenopausal women, this is the first study to randomly assign women to a low-fat eating pattern or their usual diet and to compare cancer incidence between the two groups," lead author Dr. Ross L. Prentice told Reuters Health.

Dr. Prentice, from the Fred Hutchinson Cancer Research Center in Seattle, and colleagues examined the occurrence of ovarian cancer, endometrial cancer, breast cancer, and total invasive cancer in 48,835 women randomly assigned to receive the Dietary Modification intervention or a usual diet. The subjects were followed, on average, for 8 years.

The goal of the Dietary Modification intervention is to increase the amount of fruits, vegetables, and grains in the diet and to decrease the total fat intake to 20 percent of calories, the researchers note in the Journal of the National Cancer Institute for October 17.

The Dietary Modification intervention appeared to reduce the risk of ovarian cancer, but only with long-term adherence. In the first 4 years of the study, the two groups had cancer rates that were comparable.

By contrast, in the next 4 years of the study, the intervention group had a rate of 38 cases per 1000 persons per year compared with a rate of 0.64 per 1000 person per in controls.

The Dietary Modification intervention did not affect the risk of endometrial cancer, but may have slightly reduced the risk of breast cancer and total invasive cancer.

"The take-home message for the practicing clinician is that encouraging postmenopausal female patients to undertake a change to a low-fat diet likely will reduce ovarian cancer risk, and may also reduce the risk of breast cancer and total invasive cancer," Prentice said.

"Ongoing nonintervention follow-up of trial participants may provide additional valuable assessment of the effects of a low-dietary pattern on these and other cancer incidence rates," the researchers conclude.