Soy Consumption and Premenopausal Breast Cancer Agawam MA

Scientists classify soy isoflavones from the plant Glycine max as phytoestrogens. Phyto is a Greek root word meaning plant, so phytoestrogens are plant-based compounds that have estrogen-like activity. Because they are structurally similar to estrogens, isoflavones exert weak estrogenic activity. Because of their estrogen-like effects, isoflavones have been studied for a wide spectrum of health benefits such as treating symptoms of menopause, reducing the risk of breast cancer, reducing effects of osteoporosis, supporting cardiovascular health.

Breast cancer is a physically and emotionally traumatizing disease. Unfortunately, the incidence of breast cancer has been increasing steadily for decades. In 1972 when President Nixon declared our national war on cancer, a woman's lifetime risk of developing breast cancer was 1 in 20. Today breast cancer rates have escalated to the point where women's lifetime risk of developing breast cancer is 1 in 8. Breast cancer has become the second largest cause of cancer death in women, after lung cancer, and the leading cause of death for women between the ages of 35 and 54. Breast cancer usually develops after menopause but when it develops before menopause (premenopausal breast cancer) the cancer seems to be more aggressive. The primary sign or symptom associated with breast cancer is finding a breast lump. In a survey of post-mastectomy women, the first sign or symptom of breast cancer was identified by the patient herself 80% of the time. In 19% of cases, the first signs were picked up by health professionals.

A recent study published in the American Journal of Clinical Nutrition evaluated the association of adolescent and adult soy food intake with breast cancer risk. The study included 73,223 Chinese women who participated in the Shanghai Women's Health Study. The researchers assessed the usual dietary intake during adolescence and adulthood of the women involved in the study by administering a food frequency questionnaire. The results revealed that consuming a high amount of soy foods, either soy protein or isoflavones, consistently during adolescence and adulthood was inversely associated with the risk of premenopausal breast cancer, and the relationship was highly statistically significant. There was no significant association with soy consumption and the risk of postmenopausal breast cancer. These results provide strong evidence that suggests a protective effect of soy food intake against premenopausal breast cancer.¹

¹ Lee SA, Shu XO, Li H, et al. Adolescent and adult soy food intake and breast cancer risk: results from the Shanghai Women's Health Study. Am J Clin Nutr. Jun2009;89(6):1920-1926.