Low-Fat Diet May Reduce Incidence of Ovarian Cancer in Postmenopausal Women

October 17, 2007 — A low-fat dietary pattern may reduce the incidence of ovarian cancer among postmenopausal women, according to the results of a study reported in the October 17 issue of the Journal of the National Cancer Institute.
"The Women's Health Initiative [WHI] Dietary Modification (DM) Randomized Controlled Trial evaluated the effects of a low-fat dietary pattern on chronic disease incidence, with breast cancer and colorectal cancer as primary outcomes," write Ross L. Prentice, PhD, from the Fred Hutchinson Cancer Research Center in Seattle, Washington, and colleagues. "The trial protocol also listed ovarian cancer and endometrial cancer as outcomes that may be favorably affected by the intervention."
From 1993 to 1998, 48,835 postmenopausal women were randomized to a DM intervention (n = 19,541) or to a usual diet (n = 29,294). Average follow-up was 8.1 years. The goal of the DM intervention was to decrease total fat intake to 20% of energy consumed and to increase intake of vegetables, fruits, and grains.
Pathology report review was used to confirm cancer outcomes, and weighted log-rank tests were used to compare between-group incidence of invasive cancers of the ovary and endometrium, total invasive cancer, and invasive cancers at other sites. All statistical tests were 2-sided.
Compared with the usual diet group, the DM intervention group had a lower risk for ovarian cancer (P = .03). Overall ovarian cancer hazard ratio (HR) was not statistically significantly less than 1.0, but the HR decreased with increasing duration of the DM intervention (P for trend = .01).
During the first 4 years, the risk for ovarian cancer was similar in both groups (0.52 cases per 1000 person-years in the intervention group vs 0.45 per 1000 person-years in the comparison group; HR, 1.16; 95% confidence interval [CI], 0.73 - 1.84). During the next 4.1 years, however, the risk was lower in the DM intervention group (0.38 cases per 1000 person-years in the intervention group vs 0.64 per 1000 person-years in the comparison group; HR, 0.60; 95% CI, 0.38 - 0.96).
Although the risk for endometrial cancer was not different between the groups (P = .18), the estimated risk for total invasive cancer was slightly lower in the intervention group vs the control group (HR, 0.95; 95% CI, 0.89 - 1.01; P = .10).
Limitations of the study include adjustment for multiple comparisons for risks for the 5 types of cancer studied in the trial, which may reduce the statistical significance of the findings; the lack of a consistent effect across the entire intervention period, reducing the certainty of an intervention effect; and the possibility that the cumulative hazard estimates could be distorted if ovarian cancers were detected earlier in the intervention group vs the comparison group.
"A low-fat dietary pattern may reduce the incidence of ovarian cancer among postmenopausal women," the study authors write. "The DM trial also suggests (P = .10) a possible reduction in total invasive cancer. Ongoing nonintervention follow-up of trial participants may provide additional valuable assessment of the effects of a low-fat dietary pattern on these and other cancer incidence rates."
The National Heart, Lung, and Blood Institute funded this study.
J Natl Cancer Inst. 2007;99:1534-1543.