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WHI Intranet Site
Low-Fat Dietary Pattern and Cancer Incidence
Dietary Trial (1994-2005)
Hormone Trials (1994-2004)
Calcium/Vitamin D Trial (1994-2005)
Observational Study (1994-present)
Low-fat dietary pattern and cancer incidence in the Women’s Health Initiative Dietary Modification Randomized Controlled Trial
Abstract of scientific paper in Journal of the National Cancer Institute
A low-fat dietary pattern may reduce the occurrence of invasive ovarian cancer among postmenopausal women. In the WHI Dietary Study, there were 160 cases of ovarian cancer reported among the 48,835 participants during the 8.1 years of the study's intervention phase. There were fewer new cases of ovarian cancer identified among the dietary change (intervention) participants than among the usual diet (comparison) participants. For the equivalent of every 100,000 low-fat dietary change participants per year there were 36 cases of ovarian cancer diagnosed. For the equivalent of every 100,000 usual diet participants per year there were 43 cases of ovarian cancer diagnosed. This difference was statistically significant. The probability that a difference between groups, as large as that observed, occurs by chance alone is only 3%. A probability of 5% or less is considered statistically significant.
During the first four years of the WHI Dietary Study, no effect of diet on ovarian cancer was apparent. This was anticipated in the study’s design. It can take years to see the effect of a preventive intervention on cancer risk. After the first four years of the study, there was a statistically significant 40% risk reduction in ovarian cancer among participants in the low-fat dietary change group compared to the usual diet group.
As with the breast cancer findings, the greatest reduction in cases of ovarian cancer was among dietary change participants who started with higher intakes of total fat as a percentage of calories and made the greatest reductions in fat intake. The reduced risk of ovarian cancer among the dietary change group compared to the usual diet group did not appear to be effected by the modest weight loss experienced by the dietary change group or by family history of ovarian cancer.
Among U.S. women, ovarian cancer is the seventh most common cancer and the fifth leading cause of cancer death. Ovarian cancer is a rare form of cancer among women, striking approximately 13 women out of 100,000 in the U.S. each year, which is about 1 in 60 women in their lifetimes. Compare this to breast cancer, which is diagnosed in approximately 119 women out of 100,000 each year, 1 in 8 women in their lifetimes. The mortality rate for ovarian cancer is high. Ten women out of 100,000 in the U.S. die each year from ovarian cancer. For breast cancer, 28 women out of 100,000 in the U.S. die each year. A lack of screening tools specific for ovarian cancer may be partially why the mortality rate is so high. Symptoms are non-specific and, contrary to common belief, pap smears do not detect ovarian cancer; they detect cervical cancer.
A suggestive benefit from the low-fat dietary pattern was seen for total invasive cancers. A 5% risk reduction was seen. There is, however, a probability of 10% that a risk change of this size or larger occurs by chance alone.
Background points about the low-fat dietary pattern from the WHI Dietary Study
The low-fat dietary pattern from the WHI Dietary Study that dietary change (intervention ) participants were asked to adopt included 20% of calories from total fat, 5 or more daily servings of vegetables and fruits, and 6 or more daily servings of grains. The usual diet (comparison) participants were not asked to make dietary changes. As reported previously, significant differences in dietary intake were achieved by the dietary change group whereas the comparison group’s diet remained relatively stable. By year one, the dietary change group had significantly reduced their total dietary fat from 35% to 24.3% of calories (10.7 percentage points lower than the comparison group), increased vegetable and fruit intake from 3.6 to 5.1 daily servings (1.2 servings higher than the comparison group), and increased their grain intake from 4.8 to 5.1 servings daily (0.9 servings higher than the comparison group). The dietary change group throughout the study maintained much of the dietary change but some return to previous habits did occur.