THE ROLE OF NUTRITION IN BREAST CANCER RECURRENCE RISK AND SURVIVAL

Breast cancer continues to be the most common cancer among women in the U.S.¹ and worldwide,^{1, 2} and it is the second most common cause of cancer-related death in the U.S., after lung cancer.¹  With breast cancer incidence gradually increasing and mortality rates from breast cancer decreasing,³ the American Cancer Society (ACS) now estimates that there are more than four million breast cancer survivors in the U.S. today.⁴

In part because of the large number of breast cancer survivors, there is growing interest in whether lifestyle measures outside conventional medical therapy can improve quality of life and prognosis after a diagnosis of breast cancer. A 2006 ACS position paper on diet and physical activity in cancer survivors noted that people diagnosed with cancer often wonder whether lifestyle changes may lower recurrence risk or improve outcomes.⁵ This organization’s most recent position paper highlights increasing evidence of the important role of diet; especially in the case of breast cancer, but notes that the evidence to support definitive recommendations are still lacking.⁶

Several studies have evaluated the impact of diet on breast cancer recurrence and survival, with notable insights from both randomized controlled trials (RCTs) and observational studies. Two significant RCTs are the Women's Intervention Nutrition Study (WINS)⁷ and the Women's Healthy Eating and Living (WHEL) study.⁸ WINS assessed the impact of a low-fat diet (15-20% of total daily calories from fat) on breast cancer recurrence and overall survival, while the WHEL study focused on a low-fat diet rich in fruits, vegetables, and fiber. Although a meta-analysis of these studies suggested modest effects on overall survival,⁹ the WINS study reported a 24% reduction in recurrence risk among those following the low-fat diet.

Observational studies have also provided valuable insights into the relationship between diet and breast cancer outcomes. The Nurses' Health Study (NHS), a long-running prospective cohort study of female nurses, has examined numerous health outcomes in relation to diet and other factors. This study has the unique benefit of having dietary data both before and after occurrence of disease, including breast cancer, because periodic assessment of food intake has been a central part of the study. Analyses based on these data showed that intake of a prudent (“healthy”) dietary pattern, which typically includes high consumption of fruits, vegetables, whole grains, poultry, and fish, was associated with reduced mortality from causes other than breast cancer. In contrast, a Western (“unhealthy”) dietary pattern, characterized by high intake of red and processed meats, refined grains, sweets, high-fat dairy products, and high-calorie fast food, was associated with increased mortality from non-breast cancer causes.¹⁰ Findings also showed increased survival among women eating more protein, but not red meat.¹¹

The Pathways Study is one of the first prospective cohort studies designed specifically to examine risk factors associated with outcomes after breast cancer diagnosis.¹² Among other areas, the cohort study of approximately 4,500 women is investigating various aspects of diet and lifestyle following diagnosis. Key findings among women indicate that diet quality aligned with healthy eating recommendations (such as the ACS nutrition guidelines, the alternate Mediterranean diet index (aMED), Dietary Approaches to Stop Hypertension (DASH), and the 2015 Healthy Eating Index (HEI)) around the time of diagnosis are associated with lower risks of non-breast cancer-specific and all-cause mortality.¹³ Moreover, sustained concordance with healthful plant-based diets comprised of foods such as soy foods, legumes, nuts, and seeds, is associated with lower risks of all-cause and non-breast-cancer mortality, while unhealthful plant-based diets, which can include high intakes of refined grains, sugars, and processed foods, showed opposite associations.¹⁴

Furthermore, improvements in diet quality, coupled with increased physical activity and reduced smoking post-diagnosis, were estimated to substantially lower risks of all-cause mortality over both short and long-term periods.¹⁵ Also, a post-diagnosis lifestyle score, based on alignment with comprehensive lifestyle recommendations from the ACS (which encourages fruits, vegetables, legumes, and whole grains, and discourages saturated fats), demonstrated inverse associations with all-cause and breast cancer-specific mortality.¹⁶ Finally, higher diet quality at diagnosis was associated with lower risk of cardiovascular disease events and related deaths among breast cancer patients, suggesting potential dual benefits of healthy dietary habits in this population.¹⁷

Findings from other recent publications generally align with those of the Pathways Study. The Shanghai Breast Cancer Survivors Study which included about 3,450 women who survived at least five years after a breast cancer diagnosis, found that healthy dietary patterns, including concordance with the DASH and 2015 HEI, were associated with lower risk of total mortality over the subsequent 10 years.¹⁸ Consistency with a healthy dietary pattern based on Chinese dietary guidelines also was associated with lower mortality.¹⁸ Similarly, an analysis from the Breast Cancer Family Registries that included over 6,100 women with breast cancer reported that greater alignment with healthy dietary patterns (DASH, HEI, and aMED), was associated with lower all-cause mortality, particularly among women with a body mass index less than 25kg/m² or women with hormone-receptor positive tumors.¹⁹ Analyses in over 13,000 women with breast cancer in the European Prospective Investigation into Cancer suggested that greater concordance with a healthy Mediterranean diet pattern was associated with a modest reduced risk of death over nearly nine years after diagnosis.²⁰

In conclusion, evidence from the Pathways Study and other recent research supports the growing consensus that dietary choices before and after a diagnosis of breast cancer can significantly impact prognosis. In particular, women who consumed diets that were concordant with healthy dietary patterns had a lower risk of death. While these findings do not point to specific foods or biological mechanisms, they are directly relevant to informing dietary guidelines for women diagnosed with breast cancer. Current evidence suggests that emphasizing plant foods, including whole grains, soy foods, legumes, vegetables, and fruits, is beneficial not just for the general population, but also for women diagnosed with breast cancer.

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