Eating a diet low in fat, rich in fruits, vegetables, grains, and beans—while avoiding meat, dairy, and fatty animal products—promotes breast health.

Did you know that in 2020, for the first time, breast cancer was the most diagnosed cancer worldwide? The highest incidence rates of breast cancer (new cases per population) occurred in women in high-income countries, such as those in North America and Europe.[1] The highest total number of newly diagnosed breast cancer in 2020 were in the following countries, in decreasing order – the world’s most populous country, China; USA, India, Japan, Russia, Germany & Indonesia.[2]

Why has breast cancer become so common? Is it our genes? Surprising to most people, only 5-10% of breast cancers currently prove to be hereditary based or related to gene mutations which pass from parent to child. And 87% of women diagnosed with breast cancer do not have a single first-degree relative (mother or siblings) with breast cancer. Thus, the vast majority are not due inherited mutations.[3]

In fact, lifestyle factors seem to be the key determinant for the development of breast cancer. Every day we make countless choices that bring us either closer or move us farther away from cancer. The easiest cancer to cure is the one you never get!

There is a significant body of evidence for reducing the risk of developing breast cancer (primary prevention) and improving survival of women with breast cancer (secondary prevention). Research has shown that among women who prior to menopause, exercise, do not drink alcohol or smoke, and shift their diet away from meat and dairy towards a whole food, plant predominant eating pattern cut their odds of getting breast cancer in half. And for postmenopausal women, this is cut by 80%. In the medical world, this represents and incredible triumph when you consider that women endure chemotherapy for a mere 10% average improvement in survival over those skipping chemotherapy. [4]

There is growing interest in the relationship between dietary habits and cancer. As 80% of breast cancer is fueled by estrogen, those lifestyle factors which help keep estrogen in check reduce overall risk. Longstanding evidence shows that dietary fiber may reduce circulating estrogen levels through changes in the gut microbiome and increased excretion of estrogens in the gastrointestinal tract. In addition, one type of fiber, soluble fibers are believed to decrease intestinal cholesterol absorption, and there is emerging evidence that cholesterol byproducts may have estrogenic effects.  Therefore, fiber intake is an easily modifiable risk factor to reduce the development of breast cancer and it is only found in plants.[5] Another important element is the variety of plant foods in our diet. The diversity of plants we consume is directly linked to the diversity of our gut microbiota; and this gut microbiota diversity appears to be an essential component of our overall health, including breast health.[6]

Research[7] funded by the World Cancer Research Fund found that women who consumed 1/4 to 1/3 cup of cow’s milk per day had a 30% increased chance for breast cancer. One cup (about 235ml) per day increased the risk by 50%, and 2-3 cups were associated with an 80% increased chance of breast cancer. For breast health, let us ditch the dairy and grab the soy. In fact, soy intake during childhood, adolescence and adult life protects against breast cancer, especially when consumed in youth. Consuming soy during childhood, more than 1.5 times per week, reduced adult-onset breast cancer by 58% in a study of Asian women in California and Hawaii.  How about women already being treated for breast cancer taking the medication Tamoxifen, which blocks estrogen’s effects on the breasts? In the Life After Cancer Epidemiology Study[8], such women were followed over 6 years and showed that those eating the most tofu and soymilk products had a 60 % reduction in breast cancer recurrence compared to women ingesting low soy amounts.

Fiber from fruits, vegetables, whole grains, and beans is especially beneficial for breast health because it helps both to eliminate excess estrogens from the body, and to maintain a healthy body weight. Overweight & obese adult women have a 50 to 250% (range based on weight) greater risk for postmenopausal breast cancer than normal weight women.[9] Being overweight or obese is the single most preventable factor related to breast cancer causation worldwide, with a quarter of all cases being due to the deadly combination of obesity and a sedentary lifestyle.[10]

Everyone agrees physical activity is important for the maintenance of a healthy body weight. But could a simple brisk walk reduce a woman’s risk of developing breast cancer? A study comparing over seventeen thousand postmenopausal women who walked briskly for 1.25 to 2.5 hours per week with those who did not showed the walkers reduced their breast cancer risk by 18 percent. [11] Women who exercise for three to four hours per week at moderate to vigorous levels (meaning unable to carry on a conversation) have 30 to 40 percent less breast cancer than sedentary women.[12] More than four hours had a 58 percent decrease in risk.[13]

Exercise also reduces insulin resistance and thereby the risk of diabetes. Proposed biological mechanisms underlying the link between diabetes, high BMI, and cancer include hyperinsulinemia, hyperglycemia, chronic inflammation, and dysregulation of sex hormone activity.[14]

Being physically active, maintaining a healthy body weight and eating a diversity of whole foods in a plant predominant diet are the key elements for breast health, and indeed the key determinants for an overall long healthy life.

References:

  1. https://www.iarc.who.int/wp-content/uploads/2021/02/pr294_E.pdf
  2. https://gco.iarc.fr/today/online-analysis-map
  3.  Funk, K. (2018). Breasts An Owner’s Manual. Nelson, Thomas., Nelson, Thomas, Inc.
  4. ibid
  5. Nelson ER, Wardell SE, et al, 27-Hydroxycholesterol links hypercholesterolemia and breast cancer pathophysiology. Science. 2013;342(6162):1094–1098.
  6. Bodai BI, Nakata TE. Breast Cancer: Lifestyle, the Human Gut Microbiota/Microbiome, and Survivorship. Perm J. 2020; 24:19.129.
  7. Fraser G, Jaceldo-Siegl K, et al. Dairy, soy, and risk of breast cancer: those confounded milks. International Journal of Epidemiology, Vol 49, October 2020: 1526–1537.
  8. N. Guha et al., “Soy Isoflavones and Risk of Cancer Recurrence in a Cohort of Breast Cancer Survivors: The Life after Cancer Epidemiology Study,” Breast Cancer Research and Treatment; 2 (2009): 395–405.
  9. A. McTiernan, “Behavioral Risk Factors in Breast Cancer: Can Risk Be Modified?” Oncologist, no. 4 (2003): 326–34.
  10. IARC Working Group on the Evaluation of Cancer-Preventive Agents, “Weight Control and Physical Activity,” IARC Handbook of Cancer Prevention, vol. 6 (Lyon, France: IARC, 2002).
  11. A. McTiernan et al., “Recreational Physical Activity and the Risk of Breast Cancer in Postmenopausal Women: The Women’s Health Initiative Cohort Study,” Journal of the American Medical Association290, no. 10 (September 2010): 1331–36.
  12. A. McTiernan, “Behavioral Risk Factors in Breast Cancer: Can Risk Be Modified?” Oncologist, no. 4 (2003): 326–34.
  13. L. Bernstein et al., “Physical Exercise and Reduced Risk of Breast Cancer in Young Women,” Journal of the National Cancer Institute, no. 18 (1994): 1403–8.
  14. J. Pearson-Stuttard et al, Worldwide burden of cancer attributable to diabetes & high BMI: A comparative risk assessment. Lancet Diabetes Endocrinol 2018; 6: e6–15.