A balanced, low-fat diet was associated with a lower risk of death from breast cancer in a large cohort of postmenopausal women who had no previous history of breast cancer.
Researchers studied nearly 49,000 postmenopausal women and found a 21% lower risk of death from breast cancer among women who followed the balanced, low-fat diet, compared with women who followed their normal diet.
This research is scheduled to be presented at the annual meeting of the American Society of Clinical Oncology.
Rowan Chlebowski, MD, PhD, of the Los Angeles Biomedical Research Institute at Harbor–UCLA Medical Center in Torrance, Calif., discussed the research during a press briefing in advance of the meeting.
About the study
The research is part of the Woman’s Health Initiative (NCT00000611), which is focused on investigating methods for preventing heart disease, breast and colorectal cancer, and osteoporotic fractures in postmenopausal women.
This trial enrolled 48,835 postmenopausal women, ages 50-79 years, with no history of breast cancer and normal mammograms at enrollment. From 1993 to 1998, the women were randomized to the study diet (n = 19,541) or their normal diet (n = 29,294).
With the normal diet, fat accounted for 32% or more of subjects’ daily calories. With the study diet, the goal was to reduce fat consumption to 20% or less of caloric intake. The study diet also required at least one daily serving of vegetables, fruits, and grains.
Dr. Chlebowski said the study diet is similar to DASH (Dietary Approaches to Stop Hypertension), but is slightly more focused on lowering fat intake.
Diet adherence
Subjects followed the study diet for a median of 8.5 years, and the median cumulative follow-up was 19.6 years.
Dr. Chlebowski noted that most women on the study diet were not able to reduce their daily fat consumption to the 20% goal. They did reduce fat consumption to 24.5% overall, which increased to 29% at the end of the intervention.
In the study-diet group, there was an average weight loss of 3%, significantly different from that of the normal-diet group (P less than .001).
Dr. Chlebowski said the weight loss indicates that subjects did adhere to the study diet, at least in part, as there was no change in physical activity among study participants. Furthermore, the researchers have evidence after 1 year that suggests subjects were incorporating more fruits and vegetables into their diets.
Breast cancer and death
At a median follow-up of 19.6 years, there were 3,374 cases of breast cancer, 1,011 deaths, and 383 deaths attributed to breast cancer.
The risk of death from breast cancer was significantly lower in the study-diet group than in the normal-diet group. The hazard ratio was 0.79 (95% confidence interval, 0.64-0.97; P = .025).
The risk of death (from any cause) after breast cancer was significantly lower in the study diet group as well, with a hazard ratio of 0.85 (95% confidence interval, 0.74-0.96; P = .01).
“Adoption of a low-fat dietary pattern reduces the risk of death from breast cancer in postmenopausal women,” Dr. Chlebowski said. “To our review, this is the only study providing randomized clinical trial evidence that an intervention can reduce a woman’s risk of dying from breast cancer.”
Dr. Chlebowski noted that the researchers have blood samples from all subjects enrolled in this study. The researchers plan to analyze those samples to further explore how the study diet affected the women and determine which components of the diet account for which effects.
The National Institutes of Health funded the study. The researchers disclosed relationships with Novartis, Pfizer, Amgen, AstraZeneca, Immunomedics, Metastat, Bayer, and Genentech/Roche.
SOURCE: Chlebowski R. et al. ASCO 2019. Abstract 520.