The Women's Health Resource. On the web since 1997.

Study Questions Health Benefits of Low-Fat Diet, but Offers Some Positive News About Breast Cancer Risk (dateline March 31, 2006)

Researchers have believed for years that a low-fat diet can reduce a woman's risk of breast cancer and other diseases, even though study results have been mixed. Now, the results of a Women's Health Initiative study of post-menopausal women are causing a wave of confusion among the scientific community. The study suggests that following a low-fat diet may not significantly reduce the overall risk of breast cancer, colon cancer, heart disease or stroke. However, the researchers caution that the results did not yield all bad news, especially in terms of breast cancer risk, and that the public should not discount potential health benefits of a low-fat diet.

To study the effect of a low-fat diet on the incidence of breast cancer, researchers followed nearly 49,000 women aged between 50 and 79 from 40 U.S clinical centers for an average of eight years. The study was part of the Women's Health Initiative program; it was funded by the National Heart, Lung, and Blood Institute of the National Institutes of Health. The results were published in the February 8, 2006 issue of The Journal of the American Medical Association.

The researchers concluded that among post-menopausal women, following a low-fat diet did not appear to result in a statistically significant reduction in the risk of breast cancer. In general, women in the study who followed a low-fat diet had the same rates of breast cancer, colon cancer, heart attacks and strokes as those who did not limit their fat consumption.

The study results have been widely reported by media worldwide. However, health experts caution that the study should not be blown out of proportion. Importantly, it only focused on women-specifically, those over age 50 who adopted a low-fat diet during middle age-and didn't take into account the different types of fat in the diet. Research has shown that while saturated fats tend to have a negative effect on health, mono- and polyunsaturated fats, such as those found in olive oil, may have a positive effect.

Moreover, according to the lead researchers from the Fred Hutchinson Cancer Research Center, the study did yield some potentially positive findings. "Women in the low-fat-diet group reduced their overall rate of breast cancer by about 9 percent as compared to the women who didn't change their eating patterns, but that difference was not statistically significant; it could have been due to chance. So at this point we're not able to say with certainty that a low-fat diet reduces the risk of breast cancer," said Ross L. Prentice, Ph.D., lead author of the study and former director of the Hutchinson Center's Public Health Sciences Division, in the Center's news release. According to the Hutchinson Center, this means that out of 10,000 women, 42 in the low-fat-diet group and 45 in the comparison group developed breast cancer each year.

In addition, the research found that a low-fat diet was associated with a statistically significant 15% reduction in estradiol, a form of blood estrogen that increases the risk of breast cancer. And, women who began the study with the highest baseline fat consumption and those who most strictly adhered to the study's dietary-fat goals did experience a 15% to 20% decrease in their risk of breast cancer.

"The bottom line is that changing to a low-fat diet may reduce breast-cancer risk, especially among women who have a relatively high-fat diet to begin with, but we don't view our data as strong enough at this time to make a broad recommendation that all women initiate a low-fat diet for that purpose," said Prentice, in the Hutchinson Center news release. "Additional follow up with these women may yield a stronger, statistically significant conclusion."

While the study did not show statistically significant reductions in the risk of other diseases, such as colon cancer or heart disease, the researchers say the study should still be viewed in a positive light. "Women can be confident that cutting back on fat and following the recommended Dietary Guidelines for Americans certainly won't hurt when it comes to maintaining a healthy lifestyle and preventing chronic disease," added Prentice. The researchers plan to do additional follow-up work that may yield different results.

Additional Resources and References

  • The study, "Low-Fat Dietary Pattern and Risk of Invasive Breast Cancer: The Women's Health Initiative Randomized Controlled Dietary Modification Trial," was published in the February 8, 2006 issue of The Journal of the American Medical Association,
  • This article references the February 7, 2006 Fred Hutchinson Cancer Research Center news release," Reducing Total Fat Intake May Lower Breast-Cancer Risk But Has Little Impact on Risk of Colon Cancer or Heart Disease,"
  • To learn more about risk factors for breast cancer, please visit