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I have heard some reports about negative side effects of soya isoflavones recently. I am vegetarian and use a lot of soy, like tofu, vegetarian sausages, and soy milk. Is it true that soya isoflavones have side effects? What do you know about this? Is there evidence that soy is dangerous?


Hi bent,

Isoflavones have estrogen-like properties and of course soy is high in these.  Because of this, soy isoflavones are linked to some side effects.  Research has demonstrated that soy isoflavones increase the production estrogen receptors in breast cancer cells.  Soy isoflavones are reported to interfere with cancer treatments.  Other research indicates that soy isoflavones can increase thyroid disease.  They also been reported to cause hypothyroidism and goiter and can lead to thyroid cancer.  Soy Isoflavones have also been reported to generate food allergies creating gastrointestinal issues.  Isoflavones have been reported to cause headaches (migraine) in some people who are allergic to them along with increased heart rate.

Personally, I don't take in soy isoflavones and I don't care for tofu.  However, there many different forms of isoflavones in botanicals (fruits, veggies, roots etc) that carry estrogen-like properties.  If you eat plants material of some kind, phytoestrogens are there.