Journal of the National Cancer Institute Advance Access published online on October 9, 2007
JNCI Journal of the National Cancer Institute, doi:10.1093/jnci/djm159
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© The Author 2007. Published by Oxford University Press.
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Low-Fat Dietary Pattern and Cancer Incidence in the Women’s Health Initiative Dietary Modification Randomized Controlled Trial
Affiliations of authors: Fred Hutchinson Cancer Research Center, Seattle, WA (RLP, GLA, MP); Department of Nutritional Services, University of Arizona, Tucson/Phoenix, AZ (CAT); Kaiser Permanente Division of Research, Oakland, CA (BC); Department of Medicine, University of California, Irvine, CA (FAH); Department of Epidemiology, University of Washington, Seattle, WA (SAAB); Department of Preventive Medicine, State University of New York, Stony Brook, NY (DSL); Medstar Research Institute/Howard University, Washington, DC (LL); Department of Obstetrics and Gynecology, University of California at Davis, Sacramento, CA (SY); Department of Medicine, University of Medicine and Dentistry of New Jersey, Newark, NJ (BS); Department of Medicine, Northwestern University, Chicago/Evanston, IL (JK); Division of Preventive Medicine, University of Alabama at Birmingham, Birmingham, AL (JMS); University of Tennessee Health Science Center, Memphis, TN (SS); Los Angeles Biomedical Research Institute at Harbor–UCLA Medical Center, Torrance, CA (RTC)
Correspondence to: Ross L. Prentice, PhD, Division of Public Health Sciences, Fred Hutchinson Cancer Research Center, 1100 Fairview Avenue North, PO Box 19024, Seattle, WA 98109-1024 (e-mail: rprentic{at}fhcrc.org).
Background: The Women's Health Initiative 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. The trial protocol also listed ovarian cancer and endometrial cancer as outcomes that may be favorably affected by the intervention.
Methods: A total of 48835 postmenopausal women were randomly assigned during 1993–1998 to a DM intervention (n = 19541) or comparison (usual diet; n = 29294) group and followed up for an average of 8.1 years. The intervention goal was to reduce total fat intake to 20% of energy and to increase consumption of vegetables, fruits, and grains. Cancer outcomes were verified by pathology report review. We used weighted log-rank tests to compare incidence of invasive cancers of the ovary and endometrium, total invasive cancer, and invasive cancers at other sites between the groups. All statistical tests were two-sided.
Results: Ovarian cancer risk was lower in the intervention than in the comparison group (P = .03). Although the overall ovarian cancer hazard ratio (HR) was not statistically significantly less than 1.0, the hazard ratio decreased with increasing intervention duration (Ptrend = .01). For the first 4 years, the risk for ovarian cancer was similar in the intervention and control groups (0.52 cases per 1000 person-years in the intervention group versus 0.45 per 1000 person-years in the comparison group; HR = 1.16, 95% confidence interval [CI] = 0.73 to 1.84); over the next 4.1 years, the risk was lower in the intervention group (0.38 cases per 1000 person-years in the intervention group versus 0.64 per 1000 person-years in the comparison group; HR = 0.60, 95% CI = 0.38 to 0.96). Risk of cancer of the endometrium did not differ between the groups (P = .18). The estimated risk of total invasive cancer was slightly lower in the intervention group than in the control group (HR = 0.95, 95% CI = 0.89 to 1.01; P = .10).
Conclusions: A low-fat dietary pattern may reduce the incidence of ovarian cancer among postmenopausal women.
| CONTEXT AND CAVEATS Prior knowledge Previously, the Women's Health Initiative Dietary Modification (DM) trial analyzed whether a low-fat diet would alter the incidence of breast cancer, colorectal cancer, chronic disease, and cardiovascular disease. Study design Randomized controlled trial of postmenopausal women who were assigned to their usual diet or to the DM intervention. Risks of invasive ovarian and endometrial cancer as well as total invasive cancer and invasive cancer at other sites for a period of 8.1 years were determined. Contributions Risk for invasive ovarian cancer was similar in the two groups in the first 4 years but reduced in the subsequent 4.1 years among women in the intervention group compared with women in the comparison group. No statistically significant differences in risk were observed among the two groups for total invasive cancer or invasive endometrial cancer. Implications A low-fat diet may reduce the incidence of ovarian cancer in postmenopausal women. Limitations Adjustment for multiple comparisons for the risks for the five types of cancer targeted in the trial may reduce the statistical significance of the findings.
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Manuscript received April 3, 2007; revised July 25, 2007; accepted August 22, 2007.
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  S. S. Young Re: Low-Fat Dietary Pattern and Cancer Incidence in the Women's Health Initiative Dietary Modification Randomized Controlled Trial J Natl Cancer Inst, February 20, 2008; 100(4): 284 - 284. [Full Text] [PDF]
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