How Soy Affects Hormones and Health

Soy contains phytoestrogens or “plant-estrogens,” which sounds bad but by out-competing estradiol, phytoestrogens can have a beneficial anti-estrogen effect in women of reproductive age.

That’s why soy and other phytoestrogens can make periods lighter and improve estrogen excess symptoms such as PMS and heavy periods. 

Food-based phytoestrogens have long been part of the human diet, so we’re adapted to them. They help to protect and buffer estrogen receptors and promote the healthy metabolism or detoxification of stronger estrogen metabolites. They may even reduce the risk of breast cancer.

👉 Tip: Phytoestrogens are naturally present in many foods including legumes, nuts, seeds, oats, peanuts, cashews, garlic, cabbage, fennel, apples, coffee, beer, dairy, and even meat. Phytoestrogens are a big part of why seeds are beneficial for women’s health.

In women of reproductive age, high-dose soy or soy supplements are so anti-estrogen that they can stop periods or impair fertility. Conversely, in men and children, high dose soy can have a detrimental pro-estrogen effect.

The other hormonal effects of soy are that it can 1) prevent the healthy uptake of iodine and therefore contribute to breast pain and other premenstrual symptoms and 2) reduce thyroid hormone by downregulating thyroid peroxidase. Thyroid suppression is less likely to be a problem if there is sufficient iodine intake.

Non-hormonal problems with soy

There’s more to soy than phytoestrogens. For example, industrially grown soy is heavily sprayed with pesticides. Soy is a common food sensitivity so can be a problem for immune conditions like endometriosis and soybean oil is high in omega-6 fatty acids which can be inflammatory.

Most of those negative effects are associated with industrially processed soy. Moderate amounts of traditionally fermented soy such as tempeh, miso, tamari (good soy sauce), and natto are beneficial not only for their anti-estrogen effect but also because they’re a valuable source of vitamin K2.

Bottom line, you can enjoy a moderate amount of tofu and soy sauce and rest assured that it’s fine for hormones.

Ask me in the comments.

Tofu, estrogen, and women's health.
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