Soybean Isoflavones are Different from Estrogen

In Vegan for Her, I talked extensively about soyfoods and the role that they may play in certain aspects of women’s health. Although lots of different foods impact health, soybeans and the foods made from them are definitely unique. It’s because they provide compounds called isoflavones.

Because isoflavones are commonly called phytoestrogens—or plant estrogens—there is confusion and concern about their effects. However, isoflavones actually have a different chemical structure from estrogen, which translates to very different effects in the body. In part, these differences are related to how estrogen and isoflavones bind to receptors in human cells.

The body contains two kinds of estrogen receptors called ER-beta and ER-alpha.  When they are activated, these two receptors can have different effects.

Some tissues have only one type of receptor or they might have more of one type than the other. Estrogen doesn’t care which type of receptor a certain tissue contains; it binds with equal affinity to both. So it has estrogenic effects wherever there are estrogen receptors.

That’s not true for isoflavones. They much prefer ER-beta. So if cells have mostly ER-alpha, isoflavones are less likely to have an effect.  This might explain why isoflavones haven’t been shown to promote bone health even though estrogen is good for bones. But isoflavones do appear to have the same benefits as estrogen in protecting skin health and reducing wrinkles. It’s not surprising since skin contains both types of receptors.

Breast tissue also contains both kinds of receptors but they act differently when they are activated. ER-alpha stimulates breast cell growth which may increase breast cancer risk. But ER-beta—the one that isoflavones bind to—inhibits cell growth. This means that, unlike estrogen, isoflavones may help protect breast health.

Because of their tissue-specific effects, isoflavones are referred to as SERMS or selective estrogen receptor modulators. It means that they sometimes act like estrogen and sometimes have opposite effects of estrogen, or no effects at all. So we can’t predict how isoflavones will act just by looking at what estrogen does. They aren’t the same. The table below compares the effects of estrogen and isoflavones in different tissue.

How Estrogen and Isoflavones Compare



How they work

Bind to estrogen receptors in cells.

Bind to estrogen receptors in cells.

Receptor preferences

Bind with equal affinity to ER-alpha and ER-beta. These two types of receptors can have different (and sometimes opposite) effects when activated.

Preferentially bind to ER-beta.  Tissues that have more ER-beta may respond more to isoflavones than tissues that have more ER-alpha.

Hot flashes

Reduce frequency and severity

Reduce frequency and severity

Blood clots

Stimulates formation

No effect


Reduce bone loss and fracture risk

Mixed results but seem to have no effects on bones

Heart health

Improve health of cells lining the blood vessels

Improve health of cells lining the blood vessels

Breast cancer

Effects of estrogen on breast cancer are unclear

May reduce breast cancer risk if consumed early in life. May reduce recurrence in women who have been diagnosed with breast cancer.


Increases levels

No effect or reduces levels

Questions or comments? Join me in the forum. And check out JL’s Vegan Soy Curl Mac’n Cheese recipe!

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