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Study: Low-Fat Diet Does Little to Reduce Breast Cancer Risk

February 7, 2006

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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.

In an article in the same JAMA issue, Barbara V. Howard, Ph.D., of Medstar Research Institute/Howard University, Washington, D.C., and colleagues with the WHI, analyzed data from the WHI Dietary Modification Trial to determine the effect of a diet low in fat intake and high in consumption of vegetables, fruits and grains on cardiovascular disease (CVD) and coronary heart disease (CHD) risk.

After an average of 8.1 years of follow-up, levels of low-density lipoprotein cholesterol and diastolic blood pressure were significantly reduced. Levels of high-density lipoprotein cholesterol, triglycerides, glucose and insulin did not significantly differ in the intervention vs. comparison groups.

The researchers found that the diet had no significant effects on incidence of CHD, stroke, CVD, or heart attack. Trends toward greater reductions in CHD risk were observed in those with lower intakes of saturated fat or trans fat or higher intakes of vegetables/fruits.

"To achieve a significant public health impact on CVD events, a greater magnitude of change in multiple macronutrients and micronutrients and other behaviors that influence CVD risk factors may be necessary," the authors conclude.

Regarding the latter findings, Cheryl A. M. Anderson, Ph.D., M.P.H., and Lawrence J. Appel, M.D., M.P.H., of Johns Hopkins University Bloomberg School of Public Health and School of Medicine, Baltimore, write, "Despite null findings from the WHI Dietary Modification Trial, dietary changes can have powerful, beneficial effects on CVD risk factors and outcomes.

�To reduce the risk of CVD, individuals should maintain a desirable body weight, be physically active, avoid tobacco exposure, and eat a diet consistent with national guidelines,� the writers conclude.

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