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!
@Brindi Veganism is very do-able. B12 supplementations are available and most people are recommended to take them, even non-vegans.
This is to expand on my comment from March of this year. The Japanese have an eating fermented soy hundreds if not thousands of years. They evolve to understand that it was important to eat sea vegetables to balance the possible thyroid issues with the soy. Many people will find Sea Vegetables to have a peculiar fishy or strong taste. Dulse has a very mild flavor and can’t even be lightly toasted. Eating iodine rich foods cannot hurt and are very important when eating soy fermented or not.
Suggest sea vegetables will help. Proved by Japanese.
Vegetarian is a do-able diet. Veganism is not. Note: B12 in particular. The “anti vegan propaganda” is actually truthful. It’s not a good, wholesome diet and pretending it is only disservices yourself and those you convince around you.
Great article! I’m forever explaining some of this to pals with thyroid issues. Although it’s true that fermentation of soybeans increases the bio-availability of isoflavones, having any sort of soybean when you have thyroid issues is playing Russian Roulette, particularly if one has Hashimoto’s. Counteracting the uptake of isoflavones with Iodine does not necessarily solve the problem either. Thyroid dysfunction and goiter prevalence in Japan is quite high in coastal regions and it is assumed that it is due to their high consumption of iodine even though their overall consumption is not ‘that’ much higher than many western countries. Also depending on one’s gut flora, non-fermented soy products such as tofu and soymilk can still be fermented in the gut resulting in a higher uptake of these isoflavones. If one has a thyroid issue caused by nutrient deficiencies, then fix these deficiencies before having soy (in any form) in moderation. If one has Hashimoto’s, they should avoid all soy products, not only because they’re goitrogens, but because they’re very inflammatory. If it’s vitamin K2 that you’re after there are many sources. I personally get MK7 from natto occasionally and mostly from fermented veggies such as sauerkraut and kimchi. I get MK4 from eggs, sparingly from gouda cheese and emu oil which has high amounts of it and can even be absorbed via the skin. Emu oil also has anti-inflammatory properties.
As with everything, weigh pros and cons. Miso contains dipilocolonic acid, an alkaloid that chelates heavy metals and guards against radiation. During the nuclear bombing of Nagasaki, it protected a doctor and his staff from nuclear fallout. I quit my soy lattes, but miso stays! ncbi.nlm.nih.gov/pmc/articles/PMC3695331/
“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!” Ok well let’s see about some of the low fat plant based sources of iodine….baked potatoes 40% of RDV in one serving,strawberries, bananas and of course cranberries which provide 267% of the RDV in 4 ounces. In fact half of the foods on the list of 25 foods that have the most iodine are fruits and vegetables. So actually an adult with a fully functional brain can rather easily construct a plant based diet composed of vegetables, fruit, nuts and whole grains that provide EVERY essential amino acid, essential Vitamin and essential minerals. So your posts would carry a lot more weight if you left out the antiquated anti-vegan propaganda….Particularly, since is just another diet marketing term similar to Paleo in order to sell people unnecessary products. Plant based is not a diet or a marketing term… it is simply the best and healthiest source of the micro nutrients your body needs. And if you doubt that, get a complete blood panel done before, switch to a plant based diet and redo the blood panel. The proof is in the peer reviewed scientific literature and your blood test results. Good advice is to turn and walk away quickly from anyone who speaks about nutrition at a high level or makes generalized references about how a particular diet is “missing” important nutrients.
No one mentions the effects of soy in any form, regarding estrogen and how it encourages breast cancer.