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!
Thanks I will look for it and give it a try! I also am not sure what to think about his sugar,fructose,sucrose article awhile back.
Phew! I was afraid my uncle's fabulous, and butter and cream rich, terriaki was off the menu. Glad to know what sets it apart is why it is still healthy. You had me scared there for a few paragraphs.
There is an exception. If you already have thyroid problems, such as Hashimotos's or Graves, (and sometimes iodine can exacerbate them) having soy even in this manner can make the problems worse. But if your thyroid is functioning normally I would think that this would work. I do miss my Miso soup and fermented soy sauce for marinades. Thank you so much for your column. I read it or watch it every time you put a new one up.
Hi Pure Mothers, not sure I fully understand your question. The point for all the soaking, sprouting etc is to make the food fully digestible. The body will absorb what it needs. You should always soak, sprout, or sour leaven your spelt flour! Ignoring the very dangerous long term effects of consuming phytic acid from flour prepared via modern methods is a recipe for IBS, other intestinal ailments, or worse, colon cancer. People today are so mineral deficient that the arguments FOR phytic acid borderline on the ridiculous. There are other antinutrients besides phytic acid in improperly prepared grains! Thanks for letting me know about the Alpro Soy milk .. I've already blocked Silk soy milk, will block this one too.
HI Janelle, there is nothing in the fermentation of the soy sauce to eliminate the isoflavones from what I could see from Chris' research (see link for cited source in the post). Sauerkraut has different type of goitrogen that is not increased by fermenting, but is not reduced either. Small amounts as a condiment should be fine .. if you have thyroid issues you may decide to choose to not eat it, but that is something you will have to experiment with to see what is best for you.
Sarah, I asked nutritionist about this article and he wanted me to provide scientific evidence that the organic type of soy is groitegenic. The nutritionist said that the organic type of soy will not effect thyroid because it is organic. Would you please provide the scientific evidence to back up this article? Thank you
I love the Real Food Media Network posts, although my family is vegan + fish. We eat real food though. Not the soy replacements that look like chicken and not white pastries and other vegetarian 'junk food'. We eat whole foods – no white sugar or flour in our home. I am not averse to a tofu stir fry every couple of weeks and we use some fermented soy, as well (miso, soy sauce, tempeh). Mostly we eat beans and seeds, nuts with whole grains and lots of fresh varied veggies and fruits – with fish 1 or twice each week.
I have a question. If grains, seeds, nuts and legumes are high in phytates which can interfere with mineral absorption like zinc, doesn't it balance out that those same foods are high in zinc? Doesn't Mother Nature know what she's doing? If you soak or ferment the grains it reduces phytates. And beans are high in iron (including soybeans) but also high in phytates. Why should I be worried about not absorbing my minerals when these foods come with high amounts of them plus phytates?
Some Dr's believe that phytates play an important tole in preventing the formation of free radicals, keeping minerals at safe levels and play a role in cell growth. Some animal studies suggested that they stop the growth of cancerous tumors.
Thoughts? Should I soak my spelt flour before making pancakes or bread?
By the way,
There's a Google ad at the top of this post for Alpro Soy Milk
I am wondering though would soy sauce have the goitrogens? I read that soy sauce doesn't have isoflavones. I ask because I use it on popcorn a couple times a week along with good quality butter, but I live in the midwest (goiter belt) so its possible the raw milk and butter I get could be iodine deficient. I do Lugol's iodine about once a week hoping that will help. Also, cabbage is a goitrogen so would sauerkraut make it worse as well?
Another great post – thanks, Sarah!
Hi Natasha, I my fave is Ohsawa brand Organic Unpasteurized Soy Sauce. Thanks for reading!
Can you explain why coconut aminos would bother people too? What happens in the coconut fermentation? Love this article!
Coconut aminos are fermented and potentially high in histamines which can trigger symptoms for sensitive individuals. This doesn’t mean coconut aminos are “bad”. They are fine! But, they don’t agree with everyone digestively.
I saw this article too ad was confused. What do you use as a "soy sauce"? I have heard about Liquid Aminos, Coconut Aminos and Tamari…What do you think? My family is blended Vietnamese and we eat soy sauce! I would love to know the very best choice 🙂 And yes we do eat lots of good fats, organic pasture butter, CO etc… Thanks, love your site!