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 (either light or dark), tempeh, natto, and naturally brewed soy sauce.
Note that most forms of tofu are not fermented and hence, are 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 (Goitrogens) 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 soya lecithin contains no isoflavones, so it is safe when nonGMO and in small amounts.
Have I thoroughly confused you?
I hope not. Let’s go a step further…
Fermentation Improves Digestibility
Why is fermented soy better, then?
The real reason is that the fermentation process effectively breaks down the very high levels of phytic acid and other anti-nutrients like lectins.
This permits ease of nutrient absorption during the digestive process.
Note that soy anti-nutrients can also harm the pancreas. Fermentation prevents this damaging effect.
Cultured Soy Contains Vitamin K2
In addition, cultured 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?
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 low-fat diet which is incredibly devoid of foods containing thyroid 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!
Eating Fermented Soya Safely
Before you add fermented soy to your menu, check that the following are true for your situation.
First, check with your doctor if you already suffer from thyroid disease. In my opinion, those with thyroid issues should just avoid soy, period.
If your thyroid is in good shape, be sure to consume only small amounts of natto, miso, tempeh, or traditional soy sauce as a part of an ancestral diet. Your regular menu should include plenty of iodine-rich foods such as deep yellow butter or grass-fed ghee.
In this manner, you can enjoy the wondrous K2-loaded health benefits of fermented soy with no downside from the thyroid-suppressing isoflavones!
Hello Sarah,
thanks for your very entertaining and inspiring blog! I have read that the isoflavones are especially dangerous for young children as they interfere with the development of their reproductive systems. So if fermenting soy doesn’t remove the isoflavones then that means soy is NEVER safe for infants and young children, with or without more iodine.
Here’s an interesting review of 300 studies on the effects of endocrine disruptors: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3074428/?tool=pmcentrez:
(read especially “7. Cons: evidence for endocrine disruption during development”)
Hi Sarah
Thank you for writing this article and clarifying what Dr Mercola states, is really helpful
I am new to this site and wanted to ask you if you could help me to find out more info about this Vitamin K2 supplement , which I would like to start taking,
the only ones available on the market are made of concentrated natto or alfaalfa, which we now know, they are both goitrogenic
How could i find out if the vitamin K2 derived from natto is also goitrogenic as the natto itself, or is isolated from the goitrogenic element?
I have tried to asks few doctors online but nobody seems to about this
So frustrating
I have some slight hypothyroidism condition, I would really like to find some more information on this subject or on how to find Vitamin K2 supplements that are not derived from soy
Would you give me your insight on this?
By the way, were you able to let Dr Mercola know about this confusion? Hopefully yes!!!
Thank you sooo much
Lisa
Seems to make sense that the Asian cultures who eat large amounts of soy (mostly fermented) also eat lots of sea animals and sea vegetables (iodine). It’s amazing how if you look at traditional diets they all had worked in them a BALANCE, somehow they KNEW without all these doctors and scientists and nutritionists telling them what and how to eat.
I think this part of traditional diets intrigues me the MOST. HOW did they know, how to counterbalance these things or did nature just make it so?
Thanks – I was wondering that exact thing myself this week, as a new Asian grocery store recently opened in my town. Interesting info.
Hi Cindy, sea vegetables like kelp are an excellent source of iodine. If you have a Japanese restaurant in your community, they offer kelp salads that are soooo delicious.
Hi Sarah, I'm brand new to your site. How else do you get enough Iodine in my diet? I can not eat dairy products. I do use sea salt though. Cindy
Thank you!!! I follow Dr M and am into NT but did not know this information about goitrogens and the relationship with iodine. Very valuable!
Hi Sarah,
Good article.
Many years ago I used to be a patient of Dr. Mercola's, and among the many things he encouraged me to do to improve my health was to consume organic fruits and vegetables and grass-fed beef/dairy products. He was very big on juicing also. I also remember how serious he was about staying away from soy. He didn't want me to consume soy in any form — which was OK with me, because I was/am not into soy.
It sounds to me that he may be contradicting himself on the soy issue…
Gloria
Hi Christy, last time I checked, Mercola was not being very forthright about how much vitamin A (if any) and D was in the product or how it was processed. He claims that because it is nonfishy tasting this is a good thing but what that says to me is that it is an high heat, industrialized processed oil like all other fish oils on the market EXCEPT Green Pasture Products' fermented cod liver oil and fermented skate oil. A fish oil that is processed at high temps and has lost its fishy taste is something to seriously avoid. Fishy taste and rancid taste are completely different and again, Mercola seems quite confused on this important point.
moxxor green lipped mussel omega 3 is not heat processed.
I have to ask, what is wrong with krill oil? Mercola has a new article about avoiding fish oil and espouses the benefits of krill oil.
I saw that article on mercola.com, too. I actually knew that soy was unhealthy when I first got into natural food so I was automatically suspicious of him saying fermented soy is good for you. Soy is also one of the most common GMO foods.
Kelli C.
http://pathsofnature.blogspot.com