Dietary fat interventions in healthy postmenopausal women do not appear to lower the risk of breast cancer death, but among women who become breast cancer survivors, an intervention might reduce the risk of death, according to updated findings presented at the 2016 San Antonio Breast Cancer Symposium.1
“Compared to a usual-diet control group, women randomized to a low-fat dietary pattern had a non-significantly reduced risk of death from breast cancer and a significantly reduced risk of death after breast cancer,” said Rowan T. Chlebowski, MD, PhD, of the Los Angeles Biomedical Research Institute in California.
Across countries, age-adjusted death rates correlate linearly with total dietary fat intake, he noted.
The Women’s Health Initiative Dietary Modification primary breast cancer prevention trial (ClinicalTrials.gov Identifier: NCT00000611) randomly assigned 48,835 postmenopausal women age 50 to 79 years, with no prior history of breast cancer and normal mammograms, to undergo dietary intervention (19,541 women) or to a control/comparison group (29,294). The dietary intervention reduced dietary fat intake to 20% of calories from fat, increased fruit and vegetable intake (5 servings a day), and increased grains to 6 servings a day.
Weight loss was not a study goal. During year 1, intervention group members participated in 18 group sessions and then quarterly “maintenance” meetings. The control group participants received dietary guidelines. Baseline characteristics were well-balanced between the 2 study groups.
Overall, the percentage of calories from dietary fat declined by 13.9% in year 1 and 8.2% by year 5, Dr Chlebowski said.
By year 4, the breast cancer incidence curves between members of the control and dietary-intervention groups began to separate. During a median of 8.5 years of dietary intervention, the difference in breast cancer incidence failed to achieve statistical significance. The groups saw 53 and 27 breast cancer deaths (hazard ratio [HR], 0.77; 95% CI: 0.48-1.22).
While deaths from breast cancer were not significantly associated with dietary intervention, by the 8.5-year mark, deaths after breast cancer were (HR, 0.65; 95% CI: 0.45-0.94; P = 0.02), Dr Chlebowski noted. At the 16-year mark, deaths after breast cancer were still lower than those in the control group (234 deaths versus 443; HR, 0.82; 95% CI: 0.70-0.96; P = 0.01).
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Subgroup analysis for deaths after breast cancer showed that the dietary intervention effect was stronger for women with a baseline waist circumference of 88cm or larger and with higher baseline levels of dietary fat intake.
“Future studies of other lifestyle interventions in breast cancer settings could consider some form of a low-fat dietary pattern as a base,” Dr Chlebowski concluded.
- Chlebowski RT, Aragaki AK, Thomson CA, et al. Low-fat dietary pattern and breast cancer overall survival in the women’s health initiative dietary modification randomized controlled trial. Paper presented at: 39th San Antonio Breast Cancer Symposium; Dec 2016; San Antonio, TX.