Despite improved treatments and a significant rise in the number of survivors, breast cancer still stands as a major public health issue. The risk of breast cancer recurrence is especially important for individuals navigating additional health challenges such as obesity, metabolic syndrome, and imbalanced levels of blood glucose, insulin, and testosterone. Yet, as the old saying goes, "you are what you eat", especially when it comes to breast cancer. It is quite astonishing to see the clarity with which research now shows us that what is on our plates can significantly reduce the risk factors associated with this cancer. Following a diet abundant in plant-based foods can not only regulate our insulin levels and improve glucose management but also maintain a healthier balance of blood lipids, significantly lowering the risks associated with metabolic syndrome and breast cancer.
A recent commentary published in Clinical Cancer Research, written by Dr. Anne McTiernan, a professor of epidemiology in the Public Health Sciences Division at Fred Hutch, discusses the interplay between diet and breast cancer outcomes. It summarizes and critiques the findings of the DIet and ANdrogen (DIANA-5) trial, concentrating on the effects of a 5-year Mediterranean diet and lifestyle intervention compared to control on breast cancer recurrence. The trial involved more than 1,500 women with stage I–III breast cancer who were encouraged to adopt a Mediterranean diet rich in vegetables, fruits, whole grains, legumes, olive oil, and fish, and lower in red meat, dairy, and sweets, and to engage in 30 minutes of moderate intensity physical activity every day. Adherence to the dietary intervention and exercise routine were measured at baseline and following one year.
The DIANA -5 study revealed that over the span of five years, there was no overall effect of intervention on breast cancer recurrence rates. However, additional analysis based on the level of adherence to the diet showed some interesting details: women in the top tertile of measured adherence to the diet at one year experienced a 41% reduction in their risk of cancer coming back, compared to those who did not stick to the diet. This information becomes particularly interesting when we consider a recent, systematic review of more than 20 different dietary patterns. This review revealed that diets abundant in vegetables, fruits, whole grains, and fish, while being low in saturated fats, red meats, processed foods, and sugars are linked to a decreased likelihood of breast cancer recurrence. The review suggested that a modest increase in isoflavone intake – a mere 2 mg per day – could potentially decrease deaths specifically related to breast cancer by 17% and lower the chances of recurrence by a notable 25%. These plant-based compounds can mimic or oppose estrogen effects, offering new angles in understanding diet's role in cancer management. Although research indicated that specific dietary patterns may lower the risk of all-cause and other causes of death for women with breast cancer, the limited number and small size of these studies, as well as the diversity of diet patterns, made it impossible to draw firm conclusions about which diet pattern lowers the risk of mortality or recurrence specific to breast cancer.
The DIANA-5 results, showing a stronger impact with increased dietary adherence, raise the question of whether the effectiveness lies in the prescribed diet itself or if there are differences between patients who adhere to the diet and those who do not. Dr. McTiernan points out that the "healthy diet" prescribed in DIANA-5 was not a rigid diet plan but a set of guidelines, perhaps too loose to significantly impact diet, weight, and, consequently, cancer recurrence. For ethical considerations, both the treatment and control groups were given the World Cancer Research Fund (WCRF)/American Institute for Cancer Research (AICR) prevention guidelines. This overlap led to some blending of effects between the groups, evident in the average weight loss and positive dietary changes observed in the control group over the five years.
Essential inquiries regarding diet and breast cancer prognosis, such as what foods to consume or avoid, the necessity and extent of weight loss, and the impact of exercise, are still unresolved. While no definitive diet has been identified for breast cancer survivors, a general recommendation is to eat more vegetables, fruits, whole grains, and legumes and reduce processed foods, added sugars, red meats, and sugar-sweetened beverages for better health outcomes. If exercise is deemed adequate on its own, Randomized Controlled Trials must determine the impact of different amounts and kinds of exercise on breast cancer outcomes. To answer part of these questions, Dr. McTiernan and her team are currently testing the effects of moderate-intensity exercise on biomarkers of prognosis in women with breast cancer: the Acute Effects of Exercise in Women (ACE) trial uses several Consortium resources (CDS, Prevention Center, Specimen Processing) and includes a collaboration with the Gujral lab. This introduces a new dimension to the research, focusing not only on diet but also on the potential benefits of exercise.
This study received support from Breast Cancer Research Foundation.
Fred Hutch/UW/Seattle Children’s Cancer Consortium member Dr. Anne McTiernan contributed to this work.
McTiernan A. (2023). Diet Matters in Breast Cancer Prognosis: Clinical Trial Evidence and Questions. Clinical cancer research: an official journal of the American Association for Cancer Research, 10.1158/1078-0432.CCR-23-3195. Advance online publication.