Trends for Low-Fat Diet to Reduce Breast Cancer Risk

Armen Hareyan's picture
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Breast Cancer and Diet

According to the results of the Women's Health Initiative Dietary Modification Trial, risk of breast cancer was not significantly reduced among postmenopausal women assigned to a diet low in fat and high in fruits, vegetables, and grains. These results were published in the February 8, 2006, issue of the Journal of the American Medical Association.

Population studies suggest that approximately 30% of all breast cancers are diet related. Changing from an Asian diet to a Western diet clearly increases the risk of developing breast cancer. Obesity also increases the risk of breast cancer by approximately 50%. Researchers have long speculated that there could be a link between high-fat diets and risk of breast cancer, but study results have been mixed. In order to provide more definitive information about the role of diet in the development (or avoidance) of breast cancer, researchers conducted a large clinical trial known as the Women's Health Initiative (WHI) Dietary Modification Trial.

The study enrolled close to 50,000 women between the ages of 50 and 79 years. None of the women had a history of breast cancer. Roughly 20,000 of the women were randomly assigned to the dietary modification group, with the remaining 30,000 women forming the comparison group.

Women in the dietary modification group were asked to make dietary changes that would reduce fat intake to 20% of total energy intake, increase fruit and vegetable intake to five or more servings a day, and increase grain intake to at least six servings a day. Women in the comparison group were not asked to change their diet.

Analysis of food intake in the two study groups indicated that fat intake was indeed lower among women in the dietary intervention group. The difference in fat intake between women in the intervention group and women in the comparison group was greatest during the early part of the study, but was still apparent by year six. However, although fat intake was lower among women in the intervention group, many of the women in the intervention group continued to consume more than the recommended level of fat.

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After an average of eight years of follow-up, invasive breast cancer had developed in 3.4% of the women in the dietary intervention group and 3.7% of women in the comparison group. This small difference (9%) between groups was not statistically significant (p=0.09).

Though there was no overall effect of the dietary intervention on risk of breast cancer, there was some evidence that specific subgroups of women may benefit from a low-fat diet:

  • Evidence of a benefit was stronger in women with higher baseline fat intake.

  • Evidence of a benefit was stronger among women who adhered to the dietary recommendations.

  • The dietary intervention appeared to reduce the risk of breast cancers that were estrogen receptor-positive and progesterone receptor-negative more than other breast cancers.

The researchers conclude that among postmenopausal women, consumption of a low-fat diet does not appear to significantly reduce breast cancer risk. Because there was a trend toward a decreased risk, however, the researchers suggest that a benefit of a low-fat diet may become apparent with longer follow-up.

Comments: These data represent only an 8 year follow-up but the trends of diet to affect the incidence of breast cancer are in the right direction. It may take many more years to see statistically significant differences due to diet changes as pointed out in the accompanying editorial. These data should reinforce the concept that dietary changes need to be carried out over a life-time to have an impact on cancer incidence.

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