Women who lower their fat intake may have a reduced risk of estrogen receptor (ER)-positive/progesterone receptor (PR)-negative breast cancer. These findings were published in Cancer Epidemiology, Biomarkers & Prevention.

The relationship between diet and breast cancer has been studied extensively. In particular, the link between dietary fat intake and breast cancer risk has been a major focus of research, and it’s been thought that lower dietary fat might reduce risk of certain cancers, including breast cancer.

Between 1993 and 2005, the Women’s Health Initiative (WHI) low-fat dietary modification (DM) evaluated eating patterns among 48,836 postmenopausal women. Participants in the “intervention arm” were assigned to a low-fat diet of 40% dietary fat, in which they reduced overall fat intake by 20%, reduced saturated fat intake by 7%, and increased fruit and vegetable intake to at least five servings per day and grains to at least six servings per day. They were compared with participants who selected their own diet with a fat intake of 60%.

After an average of eight-and-a-half years of follow-up, patients in the intervention (lower fat) arm did not have a reduced risk of invasive breast cancer—or of colorectal cancer, cancer-specific mortality, or overall mortality. These patients did, however, have a specific reduced risk of ER-positive/PR-negative breast cancer during the follow-up period. As well, patients who had the highest fat intake before the study had a lower risk of breast cancer while on the intervention diet compared to when they increased fat intake again after intervention.

According to these findings, women increased their fat intake after their time on the intervention diet. The researchers found no long-term reduction in overall breast cancer risk as a result of the low-fat diet on the WHI-DM. Importantly, however, they did find a reduced risk for certain breast cancers—namely ER-positive/PR-negative—suggesting that a low-fat diet may help women prevent these breast cancers.

Reference: Thomson CA, Van Horn L, Caan BJ, et al. Cancer Incidence and Mortality During the Intervention and Postintervention Periods of the Women’s Health Initiative Dietary Modification Trial. Cancer Epidemiology, Biomarkers & Prevention. 2014 Dec;23(12):2924-35. doi: 10.1158/1055-9965.EPI-14-0922.

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