Does Soy Protein Negatively Affect Your Thyroid?

Many health publications boast the positive benefits of soy protein, but fail to mention how it affects your thyroid. Consumption of soy products actually increase your risk of developing thyroid disease. Isoflavones in soy protein act as a strong anti-thyroid agent, capable of suppressing thyroid function. Soy products also reduce the effectiveness of thyroid medication, increasing your risk of developing complications with thyroid disease. 

Understanding Soy Isoflavones

The isoflavone Genistein found in soy is a potent phytoestrogen. These chemicals behave as endocrine disruptors, or plants that act as hormones, interfering with the endocrine system. Studies in the UK have shown that large amounts of soy will disrupt the menstrual cycle, altering fertility and even changing the status of sex hormones. Researchers believe that promotion of soy as a health food will soon result in an increase in thyroid disorders.

Isoflavones not only suppress your thyroid, but also interfere with any thyroid medication you are taking. Soy protein inhibits the absorption of synthroid, so soy should be avoided altogether if you have thyroid disease.

Soy Risks

Soy-based formulas have been known to contain anti-thyroid agents since the 1950’s. Infants who are solely fed soy formula have an increased risk of developing autoimmune thyroid disease.

Studies show that these infants have 13,000 to 22,000 times more estrogen compounds found in their blood that babies fed milk-based formula or breast milk.  This equates to taking 5 birth control pills per day. Girls fed soy formula run the risk of prematurely developing, while boys are often underdeveloped.


Soy products are full of known chemicals toxin to humans and animals. These toxins are known as anti-nutrients, preventing your body from getting all its nutritional needs from foods. They also have the ability to target specific organs and cells.

One of the most dangerous chemicals found in soy products is phytic acid. The typical preparation of soy products does not neutralize phytic acid. High levels of phytic acid have been shown to decrease assimilation of magnesium, calcium, zinc, and iron. The processing of soy-based foods has also resulted in the making of carcinogenic toxins like lysinoalanine and nitrosamine.

The Soy Business

The soy industry has been encouraged for years to remove isoflavones from its products. Instead, it continues to publish reports on the health benefits of soy products. The bottom line is processed soy products in all forms are notoriously bad for your health. Healthy soy needs to go through a 2-year fermentation process, and this is completely disregarded by the soy industry.

Safe Soy Consumption

For children, especially infants, no amount of soy is safe to consume. Adults risk thyroid and other hormonal problems when consuming 30 grams or more of soy protein a day. That equates to 5 ounces of soy milk.

Read all labels when purchasing products at the store. You will find that soy is listed in many food processed food items. The USDA published a list of foods, with a total of 128 containing isoflavones. Many include vegetarian labels products like soy hot dogs, tofu, meatless burgers and soy formula.   


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