Encyclopedia of Health and Medicine

P–R
phytoestrogens Plant-based ESTROGENS, many of
which are similar in chemical structure to the estrogens
the human body produces. In plants, phytoestrogens
are part of the botanical IMMUNE SYSTEM,
helping protect the plant from fungal and bacterial
INFECTION. In humans, phytoestrogens exert a weak
estrogenic effect relative to that of endogenous
(produced within the body) or supplemental estrogen.
Though an abundance of research supports
numerous health benefits from eating foods high in
phytoestrogens, questions remain about the effectiveness
of phytoestrogens in supplement forms as
well as the precise mechanisms and consequences
of them in the human body.
DIETARY SOURCES OF PHYTOESTROGENS
Isoflavones Lignans Coumestans
soybeans flaxseed red clover
SOY-based foods flaxseed oil pinto beans
red clover lentils lima beans
textured vegetable protein carrots split peas
soy protein isolate oat bran alfalfa sprouts
soy milk oatmeal red clover sprouts
licorice
asparagus
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There are two main classifications of phytoestrogens:
isoflavonoids (isoflavones) and lignans.
Soybeans are the primary source of isoflavones
such as genistein and daidzien, and nuts and flax
are the primary sources of lignans. A third classification
of phytoestrogens, coumestans, appears to
have an even stronger estrogen effect in the body
though research has not focused on them. Red
clover and alfalfa, especially sprouts, contain
coumestans. Most plants have combinations of
phytoestrogens with one that is dominant. Supplements
prepared from extracts of these substances
often combine the various phytoestrogens
into formulas for specific uses, such as MENOPAUSE
symptoms or DYSMENORRHEA (difficult menstrual
periods or menstrual cramps).
The primary therapeutic uses for phytoestrogens
are to improve the discomforts of PREMEN-
STRUAL SYNDROME (PMS) and menopause. Some
studies support the value of some phytoestrogens,
notably isoflavones, in preventing or limiting
PROSTATE CANCER and BREAST CANCER though health
experts do not agree on the extent to which these
actions result from the isoflavones. Studies using
isoflavone extracts in supplement form produce
less conclusive findings than those studies that
use isoflavone-containing (SOY-based) foods.
Isoflavones may also help reduce the risk for CAR-
DIOVASCULAR DISEASE (CVD) by lowering blood cholesterol
levels and for OSTEOPOROSIS by aiding the
bones in retaining calcium. Some studies show soy
has limited ability to slow osteoclastic activity
(bone destruction) and promote osteoblastic activity
(bone construction).
Because their chemical structures are similar to
those of endogenous estrogens, phytoestrogens
are able to bind with estrogen receptors (specialized
molecular “switches” in cells) in the body.
However, the bond is an incomplete fit and more
fragile than the bond of endogenous or supplemental
estrogen, and produces a weaker estrogen
response. Health experts disagree on the role this
weaker bond and response may play in reducing
the risk for breast cancer in women. Some believe
phytoestrogens, because they occupy estrogen
receptors, prevent more potent endogenous estrogen
from binding and thus suppress estrogen
availability. Less estrogen means less fuel for
potential CANCER cells, theoretically inhibiting their
ability to manifest as breast cancer.