Unfermented soy is poison to hypoT's - no ifs ands or buts. It suppresses thyroid function via both its goitrogens and phytoestrogens. It works so well that it is often used for hyperthyroid patients to help relieve some of their symptoms. One study on human subjects who consumed just one ounce of unfermented soy per day for three months showed depressed thyroid function, with some of them developing goiters. They all returned to normal after discontinuing the soy.

Here is a pretty detailed interview on Soy at thyroid.about.com:

http://thyroid.about.com/od/bookssu...interview_2.htm