Soy protein is NOT the health food that the media says it is. Check out these links for more information:
http://soyonlineservice.co.nz/thyroid.htm
http://thyroid.about.com/cs/soyinfo/a/soy.htm
http://thyroid.about.com/od/thyroidbasicsthyroid101/ss/preventthyroid_4.htm
Soy protein inhibits thyroid peroxidase, which is the enzyme that makes thyroid hormones (T3 & T4).
Some more on soy (copied from a thyroid forum):
"Soy is absolutely evil for thyroid patients, as it blocks thyroid hormones made by the gland, blocks absorption of thyroid medication and also blocks thyroid hormones at the cellular level. Do a search on soy and thyroid for more information."
"The soy component as mentioned by LeslieB is a very important one. If you are consuming any soy, it might take a hint of thyroid problem and make it much worse. A single ounce of tofu makes me very fatigued, brain foggy and cold for about 3 days. A soy burger twice a week would keep me in a perpetual fog."
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