Soy milk and other soy bean derived products have been widespread in the United States for over 20 years. Soy milk has been touted as a healthy alternative to cow's milk and as being more environmentally sustainable. The National Cancer Institute began funding research into possible cancer-protective benefits of soy beans in the early 1990s. Since that time, research has been conflicting, with some studies concluding that soy products reduce the risk of breast cancer, while others warning of soy's cancer-promoting properties.
Fermented Soy and Soy Milk
Soy products were initially proclaimed to be miracle foods in the United States, as it was noted that Asians consumed soy and had lower incidence of some cancers, such as breast cancer, and other diseases. However, according to "Contemporary Nutrition," Asians usually eat soy products as a condiment, and then only fermented varieties, such as natto, miso and soy sauce. Fermented soy is better absorbed, assimilated and has fewer toxic compounds compared to soy milk, which is made from soy protein isolate. Soy protein isolate is a protein-rich powder derived from waste products of soy oil manufacturing and contains compounds that block absorption of minerals, inhibit digestive enzymes and mimic hormones in humans.
Phytoestrogens
Soy milk also contains phytoestrogens, which are chemicals that mimic the effects of estrogen in the body. According to "Biochemical, Physiological and Molecular Aspects of Human Nutrition," increased levels of phytoestrogens within men invariably cause hormone disruption, which can lead to testosterone suppression, reduced libido, lethargy, prostate enlargement and gynecomastia, or breast enlargement. Although estrogen is considered a "female hormone," too much phyoestrogen can cause infertility, hypothyroidism and cancers that depend on estrogen for growth, such as breast cancer.
Soy and Breast Cancer
The phytoestrogens in soy milk are called isoflavones, which have been identified in some studies as promoting estrogen-dependent breast cancer growth, as cited in "Human Biochemistry and Disease." Specifically, genistein, the primary isoflavone in soy beans, stimulates growth of estrogen-receptor positive breast cancer cells in vitro, just as estrogen does, which is why anti-estrogen drugs such as tamoxifen are used on breast cancer patients with good success. Due to these findings, some medical authorities, such as the Cancer Council of New South Wales, warn breast cancer patients to avoid foods rich in soy because they can accelerate tumor growth. Further, some critics of soy claim that diets in many Asian countries with low cancer rates don't include soy milk and other unfermented soy products; instead, they consume much higher amounts of fresh fruits and vegetables and some fermented soy foods.
Support for Soy's Protective Effects
According to "Nutrition and Public Health," early evidence in support of soy preventing cancer began in 1990 with a study that found soy-fed rats developed 50 percent fewer breast tumors, and a 1991 study that found soy-fed women in Singapore showed a 50 percent reduction in pre-menopausal breast cancer risk. More recently, the Life After Cancer Epidemiology, or LACE, study was published in a 2009 edition of "Breast Cancer Research and Treatment" and concluded that American women given isoflavones showed reduced risks of breast cancer recurrence, especially if they were also on tamoxifen therapy. The National Cancer Institute's current position is that, "Isoflavone phytoestrogens display mild estrogen-like activities which may regulate hormone balance and reduce the risks of breast cancer, heart disease, and osteoporosis."
References
- "Contemporary Nutrition"; Gordon M. Wardlaw; 2010
- "Biochemical, Physiological and Molecular Aspects of Human Nutrition"; Martha Stipanuk; 2006
- "Biochemistry of Human Nutrition"; George Gropper; 2000
- The Daily Telegraph - Australia: Soy Cancer Warning; Jan. 14, 2007
- "Nutrition and Public Health"; Sari Edelstein; 2006
- "Breast Cancer Research and Treatment"; Soy Isoflavones and Risk of Cancer Recurrence in a Cohort of Breast Cancer Survivors: the Life After Cancer Epidemiology Study; N. Guha et al.; April 2009
