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Low-Fat Diet Ineffective Against Chronic Disease
Study shows no significant effect on cancer, cardiovascular disease
Jeff Leach (zinjboss)     Print Article 
Published 2006-02-10 11:32 (KST)   
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 Feb. 8 issue of the Journal of the American Medical Association.

In one of the studies, Ross L. Prentice, 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% 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%, n = 19,541) or the comparison group, who were not asked to make dietary modifications (60%, 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%) women in the intervention group and 1,072 (3.66%) 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 non-significant 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.

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.

In a related article in the same issue of the journal, Shirley A. A. Beresford, 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% per year) in the intervention group and 279 (0.12%) 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.

In a third and final article published in the journal, the WHI Dietary Modification Trial, Barbara V. Howard, Medstar Research Institute at 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.

In an editorial accompanying this final article, Cheryl A. M. Anderson and Lawrence J. Appel Johns Hopkins University Bloomberg School of Public Health and School of Medicine, Baltimore say that "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."
Jeff Leach is an anthropologist who specializes in evolutionary trends in human nutrition and its application to modern health and well-being. You can read more at his Web site. He also writes a FREE weekly newsletter on nutrition and health, also available on his Web site.
©2006 OhmyNews
Other articles by reporter Jeff Leach

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