Rowan Chlebowski, MD, PhD
Women who eat a balanced, low-fat diet and daily portions of vegetables, fruit, and grains have a 21% lower risk of dying from breast cancer, according to research that will be presented at the 2019 ASCO Annual Meeting.1
Given the inconsistent findings of previous observational studies, and the fact that countries with lower fat diets tend to see less instances of breast cancer, the Women’s Health Initiative (WHI) Dietary Modification (DM) clinical trial was created to examine the impact of a low-fat diet on breast cancer incidence and mortality.
At a press cast ahead of the meeting, lead author Rowan Chlebowski, MD, PhD, FASCO, explained that this was the first large, randomized clinical trial to show that diet can reduce the risk of dying from breast cancer.
Chlebowski, of the Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center in Torrance, CA, explained that from 1993-1998, investigators enrolled 48,835 postmenopausal women ages 50-79, with no previous breast cancer history, from 40 clinical centers across the United States. These women also had diets where 32% or more of their calories came from fat.
Participants were randomized into two groups: 29,294 (60%) were assigned to a usual diet comparison group, while 19,541 (40%) were placed in a dietary intervention group with the goal of reducing their daily fat intake to 20% of their calories and to increase their intake of fruits, vegetables, and grains.
The comparison group was seen once a year by researchers, while the intervention group was seen at 18 visits over the course of a year, followed by quarterly follow-up visits. The dietary intervention ended after 8.5 years (in 2005), and the trial has followed participants for a median of 19.6 years.
Between 1993 and 2013, 3,374 cases of breast cancer were diagnosed in the entire trial population.
In the data being presented at ASCO, researchers have found that the women in the reduced-fat diet group saw more health benefits compared to those in the control group. Most notably, the risk of death from any cause after a breast cancer diagnosis was reduced by 15%, and the risk of death directly from breast cancer was reduced by 21%. Throughout the dietary intervention period of 8.5 years, investigators found 8% fewer breast cancer diagnoses overall.
Chlebowski noted that these findings were particularly interesting given that the intervention group did not hit its target goal of reducing fat intake to 20% of total energy, but still managed to see significant benefits while only reducing their intake to 24.5%.
During the presscast, Chlebowski also mentioned a separate study that will be presented at ASCO, investigating the same dietary modification in women with poor metabolic factors such as diabetes and high blood pressure.2
This population–which currently includes more than 5 million women in the US–is three times more likely to die from breast cancer than women with normal metabolic function. Given their findings, Chlebowski said that they have identified a subgroup of postmenopausal women at high risk of death from breast cancer that are more likely to benefit from the dietary interventions investigated in his study.
In conclusion, Chlebowski explained, this research shows that dietary changes can significantly influence a woman’s risk of dying from breast cancer.
“This is a dietary change that we think can be achievable by many because it represents dietary moderation that was achieved by 19,000 participants,” he said. “The balanced diet we designed is one of moderation, and after nearly 20 years of follow-up, the health benefits are still accruing.”
Dr. Lidia Schapira, MD, FASCO, ASCO Breast Cancer Expert, was also on the press cast and echoed Chlebowski’s statements. “This helps us understand that what we put on our plates matters,” Schapira said. “It helps us, in general, to say that it is worth coaching our patients to put fruits, vegetables and grains on their plates.”
- Chlebowski RT, Aragaki AK, Anderson GL, et al. Low-fat dietary pattern and long-term breast cancer incidence and mortality: The Women’s Health Initiative randomized clinical trial. Presented at: ASCO Annual Meeting; May 31-June 4, 2019; Chicago, IL.; Abstract 520.
- Pan K, Aragaki AK, Neuhouser M, et al. ASCO 2019, Abstract #1539.