Maybe you’ve come across phytoestrogens while scrolling through social media. Or maybe this is the first time you’re hearing about them. Either way, the name itself can be confusing and sometimes misleading.
So, what are these compounds? And do they actually behave like oestrogen once they’re inside your body?
What Are Phytoestrogens?
“Phyto” means plant. And phytoestrogens are plant compounds shaped a little like oestrogen. Because of this, phytoestrogens may interact with the same receptors as oestrogen.
Generally, phytoestrogens fall into three main groups:
- Isoflavones: This is the most studied group, found in soy foods such as tofu, tempeh, miso, natto, soy milk, and edamame.
- Lignans: This group includes flaxseeds, along with sesame seeds, whole grains, and a range of fruit and vegetables.
- Coumestans: These are found in alfalfa and clover sprouts, and in split peas.
If you eat a varied diet, you’re almost certainly eating phytoestrogens already, whether or not you eat soy.
Do Phytoestrogens Actually Act Like Oestrogen?
Phytoestrogens do bind to oestrogen receptors. But your body has two types, alpha and beta, and your own oestrogen binds to both of them fairly equally. Genistein, the main isoflavone in soy, doesn’t. It binds far more strongly to the beta receptor than the alpha one.
In fact, the alpha oestrogen receptors are linked with proliferative effects in tissues like the breast. In other words, phytoestrogens aren’t simply a weaker version of oestrogen. They’re selective, and they behave differently in different tissues.
Interestingly, people in Japan and China average 25 to 50 mg of isoflavones a day, while the UK average is around 2.3 mg. But Japan also has the highest life expectancy in the world. At the same time, it would be a stretch to hand the credit to soy. Japanese diets also tend to be high in seafood and green tea and low in red meat, dairy, and sugar.
So, Should You Be Worried?
Some in the wellness world, most notably the late biologist Ray Peat, recommend avoiding soy because of its oestrogenic activity. While this may make sense for certain people, it doesn’t apply to everyone.
For most people, whole soy foods in normal amounts appear to be fine; a review of 14 trials found little effect on thyroid function in people with normal thyroid function and adequate iodine. High-dose supplements, however, are a different question. If you have a thyroid condition, or you’re thinking about a phytoestrogen supplement, it’s worth discussing what’s best for you with your doctor.
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