Why Fermented Soy Is Even More Goitrogenic Than Plain Soy

by Sarah Affiliate linksHealthy LivingComments: 38

fermented soy
A huge misconception in the health community is that fermented soy is safe to eat for those with thyroid issues. This would include traditional foods such as miso, tempeh, natto and naturally brewed soy sauce.

Note that tofu is not fermented and hence, is not included in this discussion. Neither are edamame beans or soyamilk.

Even leaders in the healthfood community commonly believe that fermenting soy as traditionally practiced in Asia not only breaks down the anti-nutrients, such as phytates, but also the isoflavones (plant hormones). These isoflavones are the goitrogens that can reduce thyroid function.

Isoflavones in Fermented Soy

While it is true that fermented soy is the only safe way to consume soy as the anti-nutrients are significantly reduced, unfortunately it is still very much goitrogenic (thyroid suppressing).

In fact, fermentation actually increases the bioavailability of the goitrogens!

As mentioned above, the isoflavones in soy ARE the goitrogens.  They are not reduced by fermentation, they are enhanced. This is why Asian cultures took great care to eat fermented soy foods in small condimental amounts. Celibate Buddhist monks ate them in larger quantities as they helped reduce libido and reproductive capacity.

According to the research of Dr. Chris Masterjohn, fermentation frees the isoflavones (goitrogens) from the sugars to which they are conjoined.

When a person eats unfermented soy such as bean curd, green baby soybeans, or the plethora of processed soyfoods on the market like soy milk, there is little digestive action in the human intestines to free the isoflavones from these sugars. However, when this bond is broken during fermentation via the action of the fermenting bacteria, this paves the way for much greater absorption of the isoflavones when a person consumes fermented soy!

Note that no isoflavones are contained in soya lecithin, so it is safe when nonGMO and in small amounts.

Have I thoroughly confused you?  I hope not.  Let’s go a step further.

Fermenting Soy Improves Digestibility and Creates Vitamin K2 

Why is fermented soy better, then? The real reason is because the fermentation process effectively breaks down the very high levels of phytic acid and other anti-nutrients like lectins thereby permitting ease of nutrient absorption during the digestive process. These soy anti-nutrients can also harm the pancreas.

In addition, fermentation of soy adds the MK-7 form of Vitamin K2.

According to the Weston A. Price Foundation, Vitamin K2 is the mysterious “X-Factor” referred to in the writings of Dr. Weston A. Price. This nutrient supercharges mineral absorption by the body and is very effective at preventing and repairing tooth decay.

Fermentation, then, is a double edged sword when it comes to soy. The process transforms soy into a nutrient dense food but actually increases the hormone disrupting effects of the plant isoflavones (goitrogens).

Should You Avoid Fermented Soy Too?

What to do? Is fermented soy out of the question too?

Absolutely not! Fermented soy is a nutrient dense food that is a fantastic addition to the diet with one caveat.  Fermented soy must be consumed within the context of an iodine rich diet. Therefore, if you eat the typical American lowfat diet which is incredibly devoid of foods containing thryoid protecting iodine and then suddenly decide to go wild eating fermented soy all the time because you saw something positive about it on the evening news – this could pose a problem for your thyroid health!

However, if you consume small amounts of fermented soy (natto, miso, tempeh, soy sauce) as a part of a traditional diet which includes plenty of iodine rich foods such as grassfed butter or ghee, then you are absolutely fine.

In this manner, you can enjoy the wondrous health benefits of fermented soy with no downside from the thyroid suppressing isoflavones!

Sarah, The Healthy Home Economist

The Healthy Home Economist holds a Master's degree from the University of Pennsylvania. Mother to 3 healthy children, blogger, and best-selling author, she writes about the practical application of Traditional Diet and evidence-based wellness within the modern household. Her work has been featured by USA Today, The New York Times, ABC, NBC, and many others.

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