Numerous studies have attempted to determine how overall dietary patterns are associated with increased or decreased risk of breast cancer or its recurrence. One important advantage of such studies is that they measure the effects of actual eating patterns rather than idealized diets. The main disadvantage is that it is impossible to sort out the relative contributions of individual foods or food groups that could influence risk. Such studies also tend to have inconsistent or contradictory results, in part because of differences of study design and how diet is measured. Nevertheless, the results can encourage women to move from unhealthy cancer-promoting diets to healthier eating patterns. Now a major study presented at the San Antonio Breast Cancer Symposium in December has reported that a nutritionally sound low-fat diet resulted in improved long-term survival among women with hormone receptor negative (ER-/PR-) breast cancer.
Overall diet and ER-/PR- breast cancer
Previous studies have reported the following findings concerning overall diet and hormone receptor negative breast cancer risk:
- A 2014 Spanish case-control study found that the Mediterranean diet was associated with reduced risk of breast cancer, especially triple negative (ER-/PR-/HER2-) disease.
- A large 2014 U.S. prospective study reported that high total and saturated fat were associated with increased risk of hormone receptor positive (ER+/PR+) breast cancer, but not ER-/PR- disease.
- A 2013 study of California Teachers Study participants found that a plant-based dietary pattern (high in fruit and vegetables) was associated with reduced ER-/PR- breast cancer risk whereas other common dietary patterns were not. The other dietary patterns studied were (1) a high-protein, high-fat diet (high in meats, eggs, fried foods, and high-fat condiments); (2) a high-carbohydrate diet (high in convenience foods, pasta, and bread products); (3) an "ethnic" diet (high in legumes, soy-based foods, rice, and dark-green leafy vegetables); and (4) a salad and wine diet (high in lettuce, fish, wine, low-fat salad dressing, and coffee and tea).
- A 2012 meta-analysis of eight previous population studies reported that high circulating carotenoid levels (a marker of vegetable and fruit consumption) was associated with reduced risks of both ER+ and ER- breast cancer.
- A large 2012 European study reported that adherence to a healthy Mediterranean diet excluding alcohol was associated with reduced postmenopausal breast cancer risk, especially ER-/PR- disease.
- A large 2012 Chinese study found that vegetables, citrus fruits and rosacea fruits (e.g., apples, cherries, raspberries), milk, and eggs were associated with reduced breast cancer risk, whereas other animal-source foods appeared to increase risk. These associations did not appear to vary by hormone receptor status.
- A large 2011 U.S. study of Nurses’ Health Study participants reported that a diet high in fruits and vegetables, such as one represented by adherence to Dietary Approaches to Stop Hypertension (DASH) diet, was associated with a lower risk of ER- breast cancer. In addition, a diet combining high levels of plant protein and fat with moderate intake of carbohydrates was also associated with a lower risk of ER- cancer.
- A large 2010 Australian prospective study found that high consumption of fruit and salad was associated with reduced risk of breast cancer, with stronger associations found for ER-/PR- disease.
- A large 2010 prospective study of African-American women reported that total vegetable consumption was associated with a lower risk of ER-/PR- breast cancer. In addition, there was some evidence of a reduction in overall breast cancer risk associated with cruciferous vegetable intake and for carrot intake.
- A 2009 Swedish prospective study of glycemic index and glycemic load and breast cancer risk reported no associations for ER+/PR+ or ER-/PR- breast cancer. However, a high carbohydrate intake and diets with high glycemic index and glycemic load appeared to increase the risk of developing ER+/PR- disease.
Latest research finds low-fat diet improves ER-/PR- survival
The study referenced at the beginning of this news story was designed to update results from the Women’s Intervention Nutrition Study (WINS) with respect to diet and breast cancer survival. The WINS study included 2,437 women from 39 U.S. centers with early-stage breast cancer diagnosed between 1994 and 2001. Participants were 48 to 79 years old upon enrollment. A total of 73% were lymph node negative, 79% had ER+ disease, and 70% had tumor size 2 cm or smaller. The women received standard breast cancer care (including endocrine therapy, chemotherapy and radiation treatment as clinically appropriate). Participants were randomly assigned to a low-fat diet or no dietary intervention (the control group) within six months of diagnosis.
The low-fat diet was designed to reduce fat intake while maintaining adequate nutrition. Participants in this arm of the study received eight biweekly individual counseling sessions by specially trained registered dieticians initially, followed by dietician contact every three months. The intervention lasted a median of five years. The goal was a diet consisting of 15% fat—participants achieved an average of 20% (from 29% initially). Low-fat diet participants lost an average of 6 lbs. whereas women in the control group did not lose weight.
Women in the low-fat diet group tended to have more favorable outcomes (90.2% without breast cancer recurrence) than those in the control group (87.6%) according to analysis of the data as of 2006. Women with hormone receptor negative breast cancer experienced a greater benefit from the diet than those with hormone receptor positive disease. In the last WINS update, published in 2008 after a median of 8.1 years of follow-up, there was also slightly better survival (90.9%) in the low-fat diet group compared to the control group (88.9%).
The authors currently are analyzing updated survival information after a median of 15 years of follow up based on death registry data. In a presentation and press release accompanying the preliminary study abstract, the survival rate in the low-fat diet group (86.4%) was again somewhat lower than the control group (83.0%), a result that was not statistically significant. However, based on preliminary subgroup analyses, women in the low-fat diet group with ER-/PR- cancers were found to experience a 56% statistically significant reduction in deaths. A substantial number of ER-/PR- breast cancers were also negative for HER2, making them triple-negative disease, according to study author Rowan Chlebowski, medical oncologist at the Harbor-UCLA Medical Center. He concluded that, "perhaps a lifestyle intervention targeting dietary fat intake associated with weight loss could substantially increase the chances of survival for a woman with triple-negative breast cancer.”
Please see our articles on what triple negative patients and survivors should eat and how to optimize your breast cancer diet for information on what to eat during all stages of treatment and recovery.