By Deborah Moskowitz, N.D.
"Phytoestrogen" seems to be the new buzz word
these days when discussions turn to menopause and alternatives to hormone replacement
therapy, but what are phytoestrogens and how do they affect us? Phytoestrogens are a group
of compounds found in plants that influence our own estrogen activity. They can either act
as a weak estrogen, or provide precursors to substances that affect our estrogen activity.
To understand how phytoestrogens work, it is important to understand a little about how
our hormones work in general.
Viewed simplistically, hormones are typically manufactured and released by various glands,
organs and tissues into our blood stream where they can travel to target tissues. These
target tissues contain receptor sites that are specific to certain hormones. When the
hormones bind to the receptor sites, they can initiate an effect on the target tissue.
For example, estradiol, our body's strongest estrogen, can be released from the ovary and
travel to any number of target tissues, including the breast and the uterus. At the
breast, estradiol can bind to receptor sites and increase cell division; at the uterus,
estradiol can cause the endometrial lining to thicken. These receptor sites are not so
sensitive that other substances can't bind to them.
However, just because a substance can bind to a receptor site doesn't mean it will have a
positive effect on the target tissue. Such is the case with Tamoxifen, a drug which is
used as a treatment for breast cancer. Tamoxifen can bind to estrogen receptors in the
breast without causing an increase in cell division, thereby acting as an estrogen
"blocker." At the same time, it can bind to receptors in the uterus and cause
proliferation of the endometrium. In other words, Tamoxifen can have an anti-estrogenic
effect on the breast, but have a pro-estrogenic effect on the uterus.
Phytoestrogens, such as Revival Soy
Protein can bind to estrogen receptors in our bodies and have either pro-estrogenic
effects, or anti-estrogenic effects on the target tissues. How it affects the tissues
depends in part on how much estrogen our bodies are already producing and how saturated
our receptor sites are. If our estrogen levels are low, as in menopause, empty estrogen
receptor sites can be filled with phyto-estrogens which can exert a weak pro-estrogenic
effect. (Phytoestrogens may be anywhere from 1/400th to 1/1000th the strength of
estradiol.) If our estrogen levels are high, as in some women who suffer from PMS and
endometriosis, then phytoestrogens can compete with our own estrogens for binding to
receptors. When the phyto-estrogens are successful, they decrease overall estrogen
activity because their effect on the target tissues is less than if estradiol had been
allowed to bind.
Other factors that can affect phytoestrogen activity other than its ability to bind to
receptor sites include how long it remains bound to the receptor, how rapidly it is broken
down and removed from the bloodstream and how it affects other aspects of estrogen load,
such as levels of sex steroid binding globulin.
There are hundreds of plants that contain phyto-estrogens, with some of the more
well-known including red clover, licorice, Dong quai, soy beans, flaxseeds, black cohosh
and alfalfa. Historically, many of these plants have been used to regulate hormones and
Animals have even been known to graze selectively on plants to enhance or diminish
fertility. Much of the early research on phyto-estrogens was done with animals and
interest was likely induced by the observation that sheep who grazed too much on clover
became infertile. Recently, there has been a resurgence of phytoestrogen research as more
women have demanded options to hormone replacement therapy. Furthermore, epidemiological
studies comparing native Asian women to other cultures has suggested that the high
phytoestrogen content of their diets may be responsible in part for their low rate of
breast cancer and the ease with which Asian women pass through menopause.
Certainly, more studies on women using phytoestrogens need to be done to establish both
benefits and risks. However, given the bulk of information available, phytoestrogen use
can be considered a relatively safe method of affecting estrogen activity given the
options currently in practice.