Q & A: Information about phytoestrogens

by Richard Glickman-Simon, MD

Q. Are the phytoestrogens found in soy milk and other soy products chemically different from the hormone estrogen? If someone with poor bone density is taking an anti-estrogen medication for breast cancer, can soy be safely added to the diet to increase bone density but not increase estrogen levels?

A. Compared with other women, breast cancer patients are at increased risk for osteoporosis for several reasons:

• Chemotherapy may cause the ovaries to stop producing estrogen prematurely
• Chemotherapy or the cancer itself may directly accelerate bone loss
• Anti-estrogen medications to treat the cancer may interfere with the ability of natural estrogen to preserve bone

A great deal of scientific evidence suggests that estrogen replacement therapy (ERT) is the most effective way to manage osteoporosis. But since it stimulates the growth of breast tissue, most patients with breast cancer cannot safely take estrogen. So, what are the alternatives?

Phytoestrogens

Phytoestrogens are a group of plant-based substances that are chemically similar enough to human estrogen to attach to estrogen receptors in the body. This means that they have the potential to produce estrogen-like effects in humans. The most potent type of phytoestrogen is isoflavone, which is particularly plentiful in soy and soy products. (For a more detailed discussion of soy and its associated health effects, click here.)

Two major characteristics that differentiate natural estrogen in humans from phytoestrogens in plants are:

• Phytoestrogens are biologically much weaker than estrogens. However, this is partially offset by their greater abundance in the body, particularly in post-menopausal women.
• Phytoestrogens exhibit both estrogen and anti-estrogen activity. Which way they will act is believed to be determined by:
  • The amount of circulating natural estrogen in the body
  • The number and type of estrogen receptors

Lifelong diets high in phytoestrogens may lower the risk of breast cancer. But at the same time, laboratory experiments and some clinical studies suggest that phytoestrogens have the capacity to stimulate breast tumor growth. One interesting theory explaining this discrepancy is that phytoestrogens are anti-estrogenic in the presence of lots of estrogen, as is the case in girls and younger women. But, phytoestrogens may become pro-estrogenic in low estrogen environments