The results indicate that a low-fat diet does not significantly reduce the risk of breast cancer, colorectal cancer or cardiovascular disease in postmenopausal women.

Approximately 1,000 Iowa women participated in the WHI dietary study component at the UI. More than 5,500 women overall participated in the WHI at the UI.

While the study results indicate no significant difference in breast cancer, colorectal cancer, and cardiovascular disease rates between the dietary change group and the control group, researchers noted the following:

• Breast cancer— There was not as much difference as planned between the diets of the women in the control group versus the dietary change group. Study results suggest that women who had a higher fat intake at the beginning of the study and were successful at "staying with" the study diet had the greatest reductions in breast cancer risk.
• Colorectal cancer— There was a reduction in the number of polyps and adenomas, suggesting a possible decrease in colorectal cancer risk could emerge over a longer period of time.
• Heart Disease— The WHI study diet was designed more than 15 years ago, so it focused on reducing total fat rather than specific types of fat. Research in recent years has indicated the importance of decreasing saturated and trans fat. Women on the study diet who also achieved the greatest reductions in saturated and trans fat and increases in fruits and vegetables had greater decreases in LDL (bad) cholesterol and heart disease risk.
• Weight Control— The WHI low-fat dietary pattern was not designed for weight loss. However, many in the dietary change group maintained or lost a small amount of weight. This overall slowing of weight gain is promising since obesity is on the rise in the United States. Of importance, a low-fat diet rich in fruits, vegetables and grains did not increase obesity, contrary to the claims made in popular "low-carb" diet books.

The UI researchers note that as the WHI dietary results continue to be analyzed, additional information will reveal the effect of the study diet on other diseases such as gallbladder disease, joint disease and dementia. There may be delayed effects of the study diet that will be identified in a WHI extension study, as well.

Funded by the National Heart, Lung and Blood Institute of the National Institutes of Health, the WHI is a long-term, multi-center national health study focusing on strategies to prevent heart disease, breast and colorectal cancer and osteoporosis in postmenopausal women. The study included three study components: hormone therapy, calcium/vitamin D supplements and dietary modification.

For more information:

Journal of the American Medical Association (JAMA)

WHI Study Results

National Heart, Lung, and Blood Institute