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Soy Products & Breast Cancer

Oct 24, 2010 | By Stephen Christensen
Soy Products & Breast Cancer
Photo Credit artparadigm/Digital Vision/Getty Images

Treatment for breast cancer has evolved dramatically in recent years, in large part due to the identification of hormone receptors on the surfaces of tumor cells. When stimulated, these receptors affect the growth and spread of breast cancers. New therapies have been designed to exploit this trait, and questions have arisen about the potential role of plant-based molecules, called phytoestrogens, that also attach to tumor receptors.

Phytoestrogens

More than 300 foods and herbs are known to contain phytoestrogens, chemicals from plants that mimic the effects of estrogen in the human body. Soy products boast some of the highest phytoestrogen levels, so soy has been scrutinized more closely than most other sources. Phytoestrogens belong to three major classes: coumestans, isoflavones and lignans. Hundreds of studies have examined the biological effects of these molecules, and many of these studies demonstrate health benefits. However, much of the data surrounding phytoestrogens' effects on breast cancer is inconclusive or contradictory.

Balance

One of the principal isoflavones in soy, genistein, is discussed by Dr. Duane Townsend in his book, "A Maverick of Medicine Speaks to Women." Townsend explains how genistein can act as an estrogen receptor stimulator when your estrogen levels are low and can block the effects of estrogens when your levels are high. Hence, genistein possesses the innate ability to balance the effects of estrogen in your body. Furthermore, Townsend states that genistein serves a beneficial function as an estrogen blocker in breast tumors, helps to lower your cholesterol level and even protects a man's prostate gland from benign enlargement and cancer. Townsend's views are supported by a 2010 study from the "Canadian Medical Association Journal," in which investigators demonstrated a 33 percent decrease in the risk of breast cancer recurrence among women who regularly consumed higher doses of soy isoflavones.

Controversy

Not all experts agree with Townsend's assessment of soy's beneficent properties. Although no study has convincingly linked phytoestrogens to an increased risk for breast cancer, some scientists point to studies that showed an increase in the growth of milk ducts in the breasts of women who took soy supplements. Most breast cancers arise from these ducts, leading to concerns that phytoestrogens might contribute to the development of malignant cells in these tissues. Likewise, phytoestrogens could have different and unpredictable effects on estrogen receptors in various parts of the body.

Confounding Factors

Many of the studies evaluating phytoestrogens' influence on breast cancer risk have been done on Asian women, who regularly consume more soy than Western women. Although Asian women have lower breast cancer rates than their Western counterparts, soy consumption might not entirely explain the discrepancy. Other dietary, environmental or even genetic factors could play a role. Additionally, consumption of phytoestrogens early in life might change the way estrogen receptors respond to hormonal stimulation later on. Thus, adding phytoestrogens to the diet of a woman who isn't accustomed to eating them might elicit unexpected responses.

Exercising Caution

Although much of the research surrounding soy's effects on breast cancer risk is promising, some studies show conflicting results. Women who want to reduce their risk for breast cancer or help prevent its recurrence are still bound to their health care providers, many of whom adhere to mainstream views and are hesitant to adopt unproven approaches. Until research clarifies the role of soy phytoestrogens in breast health, the choice to add them to your daily routine must be approached with caution.

References

Article reviewed by Shawn Candela Last updated on: Oct 24, 2010

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