I should probably introduce myself, I'm a LLLL in Virginia, (I was a software designer and developer before becoming a stay at home mom) and I run a website with resource information for pregnancy, childbirth and breastfeeding in my area.  There was an interesting article about a year ago about the risks of soy formula as relating to thyroid issues:
http://thyroid.about.comn/health/thyroid/library/weekly/aa083009.htm
 
"Thyroid Disease: The Dangerous Downside of Soy Products"

It's a long article, but here is an excerpt from the part relating to formula:
"The Dangers of Soy Formulas 

Since the late 1950's, it has been known that soy formulas contain anti-thyroid agents. Infants on soy formula are particularly vulnerable to developing autoimmune thyroid disease when exposed to high exposure of isoflavones over time. ( Breast and soy-formula feedings in early infancy and the prevalence of autoimmune thyroid disease in children. Fort P; Moses N; Fasano M; Goldberg T; Lifshitz F Department of Pediatrics, North Shore University Hospital-Cornell University Medical College, Manhasset, New York 11030. J Am Coll Nutr, 1990 Apr, 9:2, 164-7) This study found that the frequency of feedings with soy-based milk formulas in early life was noticeably higher in children with autoimmune thyroid disease, and thyroid problems were almost triple in those soy formula-fed children compared to their siblings and healthy unrelated children. Dr. Fitzpatrick even believes that long-term feeding with soy formulas inhibits TPO to such an extent that long-term elevated TSH levels can also raise the risk of thyroid cancer. 

Not much is being done in the U.S. to make parents aware of the thyroid-related dangers of soy formulas, or to alert the public that heavy soy consumption may be a danger to thyroid function. Other countries, however, are far ahead of the U.S. In July of 1996, the British Department of Health issued a warning that the phytoestrogens found in soy-based infant formulas could adversely affect infant health. The warning was clear, indicating that soy formula should only be given to babies on the advice of a health professional. They advised that babies who cannot be breastfed or who have allergies to other formulas be given alternatives to soy-based formulas. 

Why more information is not available about these concerns is probably a function of the tremendous strength of the large agricultural companies that dominate America's soy market. One thing is clear, however. At the same time that health experts, and nearly every radio and television health program in the nation touts soy as the miracle health food of the new millenium, the United States pediatric and medical community needs to get more on top of this issue, and begin to counsel their patients regarding the serious impact use of soy products can have on thyroid function."

The article indicates a site called soy online (http://thyroid.about.com/health/thyroid/gi/dynamic/offsite.htm?site=http://www.soyonlineservice.co.nz/) as a clearinghouse of info about the negative effects of soy.  I found it hard to tell how much was true and how much was anti-soy hype.

Pam Rubin, BSE, ME, LLLL 
Reston, VA
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Visit Birth Connections at http://www.birthconnections.com for Pregnancy and Childbirth Resources

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