Is it safe for me to eat soy foods if I have hypothyroidism?

Originally Published: June 21, 2002 - Last Updated / Reviewed On: November 18, 2011
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They say soy food is good for you, for decreased chance of osteoporosis and for an alternative to meat products. I'd like to try soy but wonder if it will affect my hypothyroidism and the prescription I use — I've read different studies on it and am confused.

Can I or can I not eat soy?

confused in Minnesota

Dear confused in Minnesota,

Soy, in addition to having some great nutritional value, also comes in many delicious forms. As you note, it can be a good meat alternative as well. It can also be an excellent alternative to dairy, not to mention, it tastes great with sushi. But the question of soy and its effect on the thyroid gland has long been one that has puzzled scientists, so your confusion is understandable. While there are theoretical concerns about the relationship between hypothyroidism and soy, current research on humans indicates that you need not avoid soy if you experience hypothyroidism, as long as you are getting iodine either in your diet or through a supplement. Also, it is unlikely that you need to worry about your medication being affected by soy, but it would be wise to double check with your health care practitioner about consuming soy with your specific prescription and dosage.

Soy foods contain some very active compounds including isoflavones, which can greatly impact health in a variety of ways. They can help lower blood cholesterol levels, protect bones against osteoporosis, and relieve some symptoms of menopause. There are two isoflavones found in soy — genistein and daidzein — which compete for an enzyme that is used to make thyroid hormone. Though animal studies have yielded some different results, problems with soy intake and hypothyroidism are only seen when a person is iodine-deficient, since iodine is needed to produce thyroid hormone.

Soy isoflavones' impact on thyroid status has been studied for years. Animal studies have been inconsistent in proving that soy intake influenced thyroid status. There have been some studies on infants born with thyroid disease which showed that, among those who were fed soy formula, increased levels of thyroid hormone replacement were necessary for regulation. The exact reason for this remains unclear. For adults with hypothyroidism, however, soy does not seem to cause any problems with the thyroid, again, as long as you have iodine in your diet.

Getting iodine in your diet is not too difficult. Iodine can be found in iodized salt, seaweed, and many types of seafood. Check out the Q&A What's up with iodized salt - Is it better for you than regular salt? for some other sources. Overall, current research indicates that you should be fine eating soy products, but if you notice any changes in your body as your intake increases, be sure to communicate this to your health care provider.

Happy soy sampling!