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, colorectal cancer or cardiovascular disease in postmenopausal women, according to three articles in the February 8 issue of JAMA.

In the first article, 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.

(JAMA. 2006;295:629-642. Available pre-embargo to the media at http://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.
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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 http://www.jamamedia.org)
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Low-Fat Diet Does Not Reduce Risk of Colorectal Cancer
In a related article, Shirley A. A. Beresford, Ph.D., of the University of Washington, Seattle, and colleagues with the Women’s Health Initiative analyzed data from the WHI Dietary Modification Trial to determine the effect of a low-fat eating pattern on risk of colorectal cancer in postmenopausal women. Previous trials examining this association have been inconclusive.

The researchers found that over the 8.1 years of follow-up, there were 201 cases of invasive colorectal cancer (0.13 percent per year) in the intervention group and 279 (0.12 percent) in the comparison group. The WHI low-fat eating pattern intervention did not reduce the risk of invasive colorectal cancers. There was no evidence of reduced risk for any category of colorectal cancer outcome associated with the intervention.

“Evidence from this study, along with that from polyp prevention trials, strongly suggests that lowering dietary fat intake and increasing fruit, vegetable, and fiber intake in mid to late life cannot be expected to reduce the risk of colorectal cancer in this length of time,” the authors write.

(JAMA. 2006;295:643-654. Available pre-embargo to the media at http://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.
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Risk of Cardiovascular Disease or Stroke Not Significantly Decreased With Low-Fat Diet

In a third article from the WHI Dietary Modification Trial, Barbara V. Howard, Ph.D., of Medstar Research Institute/Howard University, Washington, D.C., and colleagues with the Women’s Health Initiative (WHI) examined 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.

http://www.jamamedia.org

Editor’s Note: For funding/support information and the financial disclosures of the authors, please see the JAMA article.

Editorial: Dietary Modification and CVD Prevention - A Matter of Fat

In an accompanying editorial, 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, discuss the findings of Howard et al.

“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. Additional results from the WHI Dietary Modification Trial, likely forthcoming, should provide valuable evidence that will refine these recommendations and further enhance CVD prevention efforts in women.”

http://www.jamamedia.org

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Revision date: July 7, 2011
Last revised: by Janet A. Staessen, MD, PhD