Large study shows low-fat diet has little effect on reducing risk of breast cancer

A major study that includes nearly 50,000 women followed over 8 years indicates that a diet low in fat, but high in fruit, vegetables and grains, does not significantly reduce the risk of breast cancer in postmenopausal women, according to an article in the February 8 issue of JAMA.

Ross L. Prentice, Ph.D., of the Fred Hutchinson Cancer Research Center, Seattle, and colleagues with the Women's Health Initiative (WHI) Dietary Modification Trial, examined the effect of a low-fat diet on the incidence of breast cancer. The WHI, which began in 1992 with 48,835 postmenopausal women without prior breast cancer, included a dietary modification intervention consisting of consumption of a reduced amount of fat (20 percent of energy) and of an increased amount of vegetables and fruits (5 or more servings a day) and grains (6 or more servings a day). The women, aged 50 to 79 years, were randomly assigned to the dietary modification intervention group (40 percent, n = 19,541) or the comparison group, who were not asked to make dietary modifications (60 percent, n = 29,294). It has been hypothesized that a low-fat diet can reduce breast cancer risk, but previous studies have had mixed results.

The average follow-up time was 8.1 years. Overall, 655 (3.35 percent) women in the intervention group and 1,072 (3.66 percent) women in the comparison group developed invasive breast cancer during follow-up.

"Among postmenopausal women, a low-fat dietary pattern did not result in a statistically significant reduction in invasive breast cancer risk over an 8.1 year average follow-up period. However, the nonsignificant trends observed suggesting reduced risk associated with a low-fat dietary pattern indicate that longer, planned, nonintervention follow-up may yield a more definitive comparison," the authors conclude.

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(JAMA. 2006;295:629-642. Available pre-embargo to the media at www.jamamedia.org)

Editor's Note: The WHI program was funded by the National Heart, Lung, and Blood Institute of the National Institutes of Health, Department of Health and Human Services. For the financial disclosures of the authors, please see the JAMA article.

Editorial: Dietary Modification and Risk of Breast Cancer

In an accompanying editorial, Aman U. Buzdar, M.D., of the University of Texas M.D. Anderson Cancer Center, Houston, comments on the study examining low-fat diet and breast cancer risk.

"After a diagnosis of cancer, patients seek advice from their physicians and other health care professionals regarding dietary modifications that could reduce the risk of disease recurrence and also could decrease their family members' risk of cancer. In addition, many patients follow various popular diets or use complementary and alternative medicine therapies, such as various dietary supplements, which have not been evaluated in a rigorous scientific manner. In contrast, the well-designed rigorous Women's Health Initiative dietary modification study by Prentice et al provides important data that may prove useful for counseling patients."

(JAMA. 2006;295:691-692. Available pre-embargo to the media at www.jamamedia.org)


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