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Low-Fat Diet May Cut Ovarian Cancer Risk

Sticking to a low-fat diet for at least 4 years can reduce an older woman's risk of developing ovarian cancer by about 40%, according to a new study. The results are the most promising to date from a large clinical trial that's examining how low-fat diets can affect the health of postmenopausal women.

Ovarian cancer is a particularly deadly form of cancer. It affects about 1 in 60 American women in their lifetimes and kills about 15,000 each year. Ovarian cancer usually has few or no symptoms in its early stages, when it's easiest to treat. By the time symptoms appear, only about one-third of patients survive beyond 5 years.

Researchers have been examining the impact of dietary fat on ovarian and endometrial cancer in a group of 48,835 healthy, postmenopausal women who were followed for an average of 8 years. The clinical trial, known as the Dietary Modification Trial, is part of the Women's Health Initiative series of studies, which is funded by NIH's National Heart, Lung and Blood Institute (NHLBI). The new findings were reported in the October 9, 2007, online edition of the Journal of the National Cancer Institute.

When the women first joined the study, their diets had a fat content on par with the national average, with about 35% of their calories coming from fat. As the study began, about 20,000 of the women were counseled to reduce their fat intake to 20% of calories and to eat plenty of fruits, vegetables and grains. The comparison group of nearly 30,000 women received diet-related educational materials only.

By the end of the first year, the low-fat diet group had reduced their total fat intake to about 24% of calories. By the end of the 8-year study, their fat intake had creeped up to about 29%. Their fat consumption was still lower than the comparison group, however, which consumed about 37% of their calories from fat by the end of the study.

As expected, the researchers found that ovarian cancer risk was similar in the 2 groups for the first 4 years, because a diet's impact on cancer can take many years to appear. However, over the next 4 years, the risk of ovarian cancer declined significantly in the low-fat-diet group. These women were 40% less likely to develop ovarian cancer than women in the comparison group.

The researchers also found that women who started with the highest fat intake, and who reduced their fat intake the most during the study, had the greatest reduction in ovarian cancer risk. The researchers found no differences in endometrial cancer rates.

An earlier analysis of the same group of women didn't reveal any major effects of a low-fat diet on rates of colorectal cancer, heart disease or stroke. However, there were some promising trends for breast cancer and heart disease that warrant further study. These new findings support the idea that some women may be able to reduce cancer risks by lowering their dietary fats.