Soy and Thyroid

There is ample  evidence that isoflavones contain in soy products, including genistein, are toxins. Isoflavones are inhibitors of thyroid peroxidase that makes T3 and T4.

Unfermented soy products such as to tofu and infant soy formula contain:

· Allergens

· Enzyme inhibitors

· Hormone modifiers

· Mineral blockers

· Iodine blockers that interfere with thyroid function

Since the late 1950's researchers have identified that the soy is a phytoestrogen. Soy's estrogenic effect is 1/500 the potency of that estrogen naturally circulating in our body. Soy acts as an competitive inhibitor of estrogen at the cellular estrogen receptor site, reducing the effect of estrogen in our body. At the same time, over consumption of  soy can overwhelm many of the body's cell and may overload them with such weak estrogen-like hormone, resulting in overloading of hormone.

Infants fed long term soy formula during childhood are particularly vulnerable to developing autoimmune thyroid disease when exposed to high exposure of isoflavones over the years. In fact, studies have found that the frequency of feedings with soy-based milk formulas in early life was noticeably higher in children with autoimmune thyroid disease later in life. The incidence of thyroid disease  were almost triple in those soy formula-fed children compared to their siblings and healthy unrelated children.

How much is too much? This varies depending age. According to the Soy Online Service, infant should not take in any soy. For adults, just 30 mg of soy isoflavones per day is the amount found to have a negative impact on thyroid function. This amount of soy isoflavones is found in just 5-8 ounces of soy milk, or 1.5 ounces of miso. Interestingly, while miso have the phto-estrogenic effect, it does not have the enzyme inhibitory effect because it is fermented. Other fermented soy product include soy sauce or tempeh.

The current promotion of soy as a health food will likely result in an increase in thyroid disorders and possibly raise the risk of thyroid cancer in decades to come. Remember that it takes an average of 20 years before chronic insult to the body surfaces as a disease state.

The Europeans are far ahead of Americans when it comes to soy. In July of 1996, the British Department of Health issued a warning that the phyto-estrogens found in soy-based infant formulas could adversely affect infant health. Soy formula should only be given to babies on the advice of a health professional after careful consideration.  The US is far behind in such public health warnings.