I’ve never been a huge fan of soy. I don’t like soybean oil because it’s inflammatory. I don’t like processed soy protein because it impairs nutrient absorption. I don’t like industrially grown soy because it’s heavily sprayed with pesticides.
Inflammation; impaired nutrient absorption; pesticides. That’s why industrially processed soy is bad for hormones. But what about whole bean, organic, and fermented soy? Does it affect hormones? Yes, but not necessarily in a bad way.
Is soy estrogen?
Soy contains phytoestrogens or “plant-estrogens”, which sounds a bit scary. Who wants to ingest a foreign estrogen? But in reality, we ingest a lot of foreign estrogens (also called xenoestrogens).
⚠️ Xenoestrogens are not estradiol (our main estrogen). Instead, they’re chemicals that are molecularly similar to estradiol.
We’re exposed to many toxic xenoestrogens such as pesticides, plastics, and ethinylestradiol (the synthetic estrogen in hormonal birth control). Chemical xenoestrogens have been linked to many women’s health problems including PCOS, thyroid disease, endometriosis, infertility, and breast cancer.
We’re also exposed to phytoestrogens, or plant-estrogens, which are more benign. They’re naturally present in many foods including lentils, oats, peanuts, cashews, garlic, cabbage, fennel, apples, coffee, beer, dairy, and meat. Phytoestrogens have long been part of our traditional diet, so we’re adapted to them. They help to regulate and metabolize estradiol (our strongest estrogen). For example, phytoestrogens protect and buffer estrogen receptors. and they promote the healthy metabolism or detoxification of estrogen.
In the presence of high estradiol, phytoestrogens have an anti-estrogen effect. They make periods lighter and improve estrogen-excess symptoms such as PMS and heavy periods. They protect against breast cancer. See my Estrogen Excess post.
Soy’s anti-estrogen effect is so strong that too much soy can stop periods and impair fertility. Period suppression the biggest negative effect from soy I encounter in my clinic. That’s why I list soy as one of the “hidden causes of polycystic ovarian syndrome” in my 4 Types of PCOS post.
⚠️ What about men, children, and post-menopausal women? In the presence of low estradiol, phytoestrogens have a net pro-estrogen effect, which is probably harmless at a low dose, but men and children should avoid too much soy. Soy’s pro-estrogen effect and be beneficial in post-menopausal women.
How soy affects thyroid
Soy’s isoflavones inactivate the enzyme that makes thyroid hormone (thyroid peroxidase), so it can suppress thyroid hormone. That’s less likely to be a problem when there is sufficient iodine.
Bottom line: Is it safe to eat soy?
There is really no need to eat a lot of soy because there are better, more nutrient-dense foods such as meat and vegetables. But you do not need to fear small amounts of tofu and soy sauce. They might even be beneficial if you suffer from PMS or heavy periods.
Small amounts of traditionally fermented soy such as tempeh, miso, tamari (good soy sauce), and natto are beneficial because they are a valuable source of vitamin K2.
Industrially processed such as soybean oil, flour, and protein powder should be avoided.
What are your thoughts on soy? I’d love to hear from you.
Yours in health,