I listened to a radio show that had an author of this book:
"The Whole Soy Story: The Dark Side of America's Favorite Health Food" http://www.amazon.com/Whole-Soy-Sto...954&sr=1-1
I would really stay away from soy based food alltogether for a lot other reasons than its potential harm of thyroid.
According to author, soy has a number of dangerous toxina, that only get neutalized after a lengthy fermentation process (or extensive processing involving heat and chemicals). So only soy products that are safe are miso and tempeh. Tofu is not fermented.