Breast cancer is the most commonly diagnosed non-skin cancer in women, and remains a major contributor to mortality despite advances in detection and treatment. As such, identifying factors that can increase survival after a breast cancer diagnosis represents a major public health priority. Previous evidence has suggested that eating a low-fat diet may reduce the risk of developing breast cancer. In a recent issue of the Journal of Clinical Oncology, Dr. Ross Prentice and colleagues in the Public Health Sciences Division found that a low-fat diet also significantly reduced death after breast cancer.
To evaluate these relationships, the authors utilized data from the Women’s Health Initiative (WHI) Dietary Modification trial. Said lead author Dr. Rowan Chlebowski, of the Los Angeles Biomedical Research Institute, “this randomized trial represents the largest breast cancer prevention trial ever conducted.” From 1993 to 1998, nearly 49,000 postmenopausal women were assigned to either a low-fat dietary pattern intervention group or a usual diet comparison group. The low-fat dietary program was designed to reduce fat intake to 20% of total energy, as well as increase consumption of vegetables, fruits, and grains. While calorie restrictions or weight loss were not targets of the intervention, the women in the dietary modification group obtained and maintained significant weight loss. Participating women were followed over time to evaluate how these differences in dietary patterns were associated with breast cancer incidence and death.
In previous analyses of these data both during the intervention and after 8.5 years of follow-up, the authors reported that fewer breast cancers were diagnosed in the women in the intervention group, and that breast cancer mortality was also reduced, though neither reduction was statistically significant. In this paper, the authors extended these analyses to 16.1 years of follow-up and found significant benefit with the low-fat dietary pattern. While the 8% reduction in breast cancer incidence during the intervention period was not quite statistically significant, the distribution of cancer subtype did differ significantly, with a larger fraction of cancers in the dietary group being estrogen receptor positive (ER+) and progesterone receptor negative (PR-).
Importantly in the new analyses, deaths after breast cancer were significantly reduced in the dietary intervention group, with a hazard ratio of 0.82 (95% confidence interval 0.07 to 0.96). Said Chlebowski, “this result likely reflects a reduction in deaths from breast cancer and a favorable influence on deaths from other causes as well.” The number of deaths attributed to breast cancer were also lower in the low-fat diet group, though this association was not statistically significant.
Overall, this research reinforces the health benefits of lifestyle patterns such as a low-fat diet, particularly for postmenopausal women hoping to reduce their risk of breast cancer and mortality. Said Chlebowski, “subgroup analysis suggests that a modest reduction in fat intake with associated weight loss represents an easily achievable goal by many, which could favorably influence clinical outcome.”
Moving forward, the authors plan to continue identifying how a low-fat diet relates to breast cancer risk and mortality. Said Chlebowski, “future studies will address potential mediating factors including changes in insulin, adiponectin and inflammatory markers in the WHI Dietary Modification participants, along with subgroup analyses to identify women most likely to benefit from the dietary intervention.”
Also contributing to this project from the Fred Hutch were Drs. Aaron Aragaki, Garnet Anderson, and Wendy Barrington.
Chlebowski RT, Aragaki AK, Anderson GL, Thomson CA, Manson JE, Simon MS, Howard BV, Rohan TE, Snetselar L, Lane D, Barrington W, Vitolins MZ, Womack C, Qi L, Hou L, Thomas F, Prentice RL. Low-fat dietary pattern and breast cancer mortality in the Women's Health Initiative Randomized Controlled Trial. J Clin Oncol 2017; JCO2016720326. doi: 10.1200/JCO.2016.72.0326.
Funding for this study was provided by the National Heart, Lung, and Blood Institute (NIH), the National Cancer Institute (NIH), and the American Institute for Cancer Research.