P–R

phytoestrogens Plant-based ESTROGENS, many of
which are similar in chemical structure to the estro-
gens the human body produces. In plants, phytoe-
strogens 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 estro-
gen. Though an abundance of research supports
numerous health benefits from eating foods high in
phytoestrogens, questions remain about the effec-
tiveness 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

There are two main classifications of phyto-
estrogens: 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 classifi-
cation 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. Sup-
plements prepared from extracts of these sub-

stances 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 phytoestro-

gens are to improve the discomforts ofPREMEN-

STRUAL SYNDROME (PMS) and menopause. Some

studies support the value of some phytoestrogens,

notably isoflavones, in preventing or limiting

PROSTATE CANCERand BREAST CANCERthough 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 cho-

lesterol levels and for OSTEOPOROSISby aiding the

bones in retaining calcium. Some studies show soy

has limited ability to slow osteoclastic activity

(bone destruction) and promote osteoblastic activ-

ity (bone construction).

Because their chemical structures are similar to

those of endogenous estrogens, phytoestrogens

are able to bind with estrogen receptors (special-

ized molecular “switches” in cells) in the body.

However, the bond is an incomplete fit and more

fragile than the bond of endogenous or supple-

mental 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 estro-

gen from binding and thus suppress estrogen

availability. Less estrogen means less fuel for

potential CANCERcells, theoretically inhibiting their

ability to manifest as breast cancer.

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