Tofu, soymilk, miso, tempeh, edamame—these and other soy products, including the soybeans themselves, are high in nutrients you tend to associate with other legumes, including fiber, iron, magnesium, potassium, protein, and zinc. But does it have negative effects on thyroid function?
Why May Soy Bad For Your Thyroid?
Soy has so-called “goitrogenic” compounds (as do broccoli-family vegetables and flax seeds), which can interfere with thyroid function in people with marginal iodine intake. The answer is not to avoid these super healthy foods but to just make sure you get enough iodine. See my videos Avoiding Iodine Deficiency and Pregnant Vegans at Risk for Iodine Deficiency.
Is Soy Bad For Thyroid Medication?
As I discuss in my video The Healthiest Natural Source of Iodine, soy foods may inhibit the oral absorption of Synthroid, thyroid hormone replacement drugs, but so do all foods. That’s why we tell patients to take it on an empty stomach.
Conclusion
Soy has many health benefits, including improved breast cancer survival and relief of menopause symptoms. It’s also not detrimental to thyroid function as long as intake of iodine is adequate. For another reason, though, restricting one’s soy intake to 3-5 servings a day is probably a good idea. See How Much Soy Is Too Much? and Too Much Soy May Neutralize Benefits.
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