Popular Fact

Soy contains estrogen and is akin to hormone replacement therapy

Soy contains phytoestrogens which are completely different and have no effect on humans

Reality

Soy contains phytoestrogens which may interact with the human body in a variety of ways (including hormonally).
- TalkVeganToMe

See below for a more detailed explanation.
See our article on Soy is bad for you? for more on what this means.

What are phytoestrogens and isoflavones?

Phytoestrogens are naturally-occurring plant compounds that are structurally and/or functionally similar to mammalian estrogens and their active metabolites. - The pros and cons of phytoestrogens - Front Neuroendocrinol - 2010 - p2

Small amounts can also be found in animal products.

Our data show that most animal foods contained phytoestrogens, which would have been derived from animal feeds and pastures, especially those containing clover and other legumes. Furthermore, although the phytoestrogen content in animal products is low when compared to soy-based foods (e.g., soy milk), the range is similar to that of many commonly consumed vegetables.
- Phytoestrogen Content of Foods of Animal Origin: Dairy Products, Eggs, Meat, Fish, and Seafood - Journal of Agricultural Food Chemistry - 2008

What isoflavones does soy contain?

Soy contains the isoflavones:
- Biochanin A
- Clycitein
- Daidzein
- Formononetin
- Genistein
- The pros and cons of phytoestrogens - Front Neuroendocrinol - 2010 - p2

How do isoflavones interact with the body?

Some isoflavones, most notably genistein, inhibit pathways important for cell growth and proliferation, an effect which affects multiple organ systems.
- The pros and cons of phytoestrogens - Front Neuroendocrinol - 2010 - p4

In other words, it’s possible for human cell growth to be increased by phytoestrogens.

Phytoestrogens are plant‐derived [small amounts can also be found in animal products, see above] dietary compounds with structural similarity to 17‐β‐oestradiol (E2), the primary female sex hormone. This structural similarity to E2 enables phytoestrogens to cause (anti)oestrogenic effects by binding to the oestrogen receptors.
[…]
[P]hytoestrogens are also considered endocrine disruptors, indicating that they have the potential to cause adverse health effects such as infertility and increased risks of cancer in oestrogen-sensitive organs.
- The potential health effects of dietary phytoestrogens - British Journal of Pharmacology

Phytoestrogens have a similar shape to human estorogen, which enables them to interrupt the normal absorption of human estrogen in the endocrine (hormonal) system.

Phytoestrogens produce estrogenic, anti-estrogenic or no activity depending upon the tissue. [Oestrogen Receptor Alpha] and [Oestrogen Receptor Beta] display distinct expression patterns in male and female[s…].
- Soy, Soy Foods and Their Role in Vegetarian Diets - Nutrients - 2018 - p7

Phytoestrogens effects vary from one body part to another and from one sex expression to another.

From these sources we can conclude that soy’s phytoestrogens can have an effect on the human body, what exactly that effect may be is covered in more detail in Soy is bad for you?.

It’s also worth noting that a huge variety of foods contain phytoestrogens, including oats, beans, rice, coffee, apples, yams, etc. and even animal products.

Sources

Article Contributors

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