Mercola Confusion: Fermented Soy IS Goitrogenic

by Sarah Healthy LivingComments: 36

I’ve been a reader of Dr. Mercola’s alternative health newsletter for over ten years.   I love how he exposes the scams of Big Food and Big Pharma and is, in general, an advocate of Real Food (with a few glaring exceptions such as his promotion of his own protein powder and the dubious krill oil).

You can imagine my surprise when I was scanning through one of his articles from this week and came across a very confusing point regarding the subject of soy.    In this article, titled Got Thyroid Problems?  Then Stop Consuming This “Healthy” Food, Dr. Mercola writes that fermented soy is a healthy addition to the diet because the fermentation process breaks down the antinutrients, isoflavones (plant hormones), and goitrogens.    Breakdown of goitrogens?   Doesn’t that seem to indicate that they are somehow eliminated?  It did to me.

While I agree with Dr. Mercola that fermented soy such as miso, tempeh, and natto is the ONLY safe way to consume soy, he seems to confuse the fact that fermented soy is still very much goitrogenic (thyroid suppressing).

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

You see, the isoflavones in soy ARE the goitrogens.   According to the research of Chris Masterjohn in his paper Thyroid Toxins: The Double-Edged Swords of the Kingdom Plantae, fermentation frees the isoflavones (goitrogens) from the sugars to which they are conjoined.   When a person eats unfermented soy, 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!

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

Why is fermented soy better, then?   The real reason fermented soy is healthy to consume is because the fermentation process does effectively break down the very high levels of phytic acid and other anti-nutrients in the soy thereby permitting ease of nutrient absorption during the digestive process.

Fermentation can also add the critical vitamin K2 in fermented soy foods like natto.   The research of Chris Masterjohn indicates that Vitamin K2 is the mysterious “X Factor” vitamin referred to in the writings of Dr. Weston A. Price that supercharges mineral absorption by the body and is so very effective at preventing and repairing tooth decay.

Fermentation, then, transforms soy into a nutrient dense food but actually increases the hormone disrupting effects of the isoflavones (goitrogens). 

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, then you are absolutely fine. 

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

Sarah, The Healthy Home Economist

SourceThyroid Toxins: The Double-Edged Swords of the Kingdom Plantae
by Chris Masterjohn, copyright 2007

Picture Credit

Comments (36)

  • Nina

    No one mentions the effects of soy in any form, regarding estrogen and how it encourages breast cancer.

    August 16th, 2015 8:33 am Reply
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  • Carrie

    What do you think about fermented soy as part of a small ingredient in a prenatal vitamin? (Garden of Life Vitamin Code Raw Prenatal, which also has iodine.) I have Hashimoto’s thyroiditis and am having a heck of a time deciding on a prenatal. I seem to like everything else I see about it, but I just noticed the fermented soy listed in the ingredients and now I’m researching that and stumbled on this article. Thanks for the feedback!

    January 2nd, 2014 9:49 pm Reply
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  • Tom

    this post has good information–but the bit about getting iodine from eating grass fed butter–have you ever priced grass fed butter? Couldn’t you come down to earth a little and suggest something like a drop or two of Lugols iodine solution is hot water? As home economists go–you are very often nothing like economic.

    April 20th, 2013 5:09 pm Reply
  • Annmarie

    Thanks for the article. I saw that you mentioned Krill oil in the first part of the article. I recently started taking Dr. Mercola’s Krill Oil for Women. Is there something I should know about this?

    March 6th, 2013 9:34 pm Reply
  • cana

    If Chris Masterjohn is correct about fermentation making soy even more goitrogenic. Is that true with fermented cabbage too? Thanks.

    June 3rd, 2012 9:14 pm Reply
  • Queenie

    I had seen one of it’s kind here but it’s pretty expensive though some of it’s user really claims that it’s really effective but I guess it’s not still worth of it’s price. However, as my curiosity arises about this product, I think I must take a look at it and see for myself if this product really works.

    February 7th, 2012 10:26 pm Reply
  • Peter

    Sorry, I’d take Dr. Mercola’s words over Sarah’s any day.

    November 6th, 2011 5:33 pm Reply
  • Bettina

    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:

    (read especially “7. Cons: evidence for endocrine disruption during development”)

    June 3rd, 2011 10:52 am Reply
  • Lisa

    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

    March 27th, 2011 3:45 pm Reply
  • Emilee

    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?

    December 23rd, 2010 1:37 pm Reply
    • Rachel

      Thanks – I was wondering that exact thing myself this week, as a new Asian grocery store recently opened in my town. Interesting info.

      January 15th, 2012 5:24 pm Reply
  • Sarah, the Healthy Home Economist

    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.

    November 9th, 2010 12:42 am Reply
  • Anonymous

    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

    November 8th, 2010 1:54 am Reply
  • Glory Bea Farm

    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!

    October 19th, 2010 2:25 am Reply
  • Anonymous

    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…

    October 17th, 2010 7:30 pm Reply
  • Sarah, the Healthy Home Economist

    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.

    October 16th, 2010 11:35 pm Reply
    • raya

      moxxor green lipped mussel omega 3 is not heat processed.

      December 23rd, 2010 2:45 pm Reply
  • Christy

    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.

    October 16th, 2010 11:09 pm Reply
  • Kelli C.

    I saw that article on, 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.

    October 16th, 2010 10:18 pm Reply
  • Natasha @ Saved by the Egg Timer

    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.

    October 16th, 2010 8:41 pm Reply
  • Mama G

    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.

    October 16th, 2010 4:15 pm Reply
  • Mom0fTwins

    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.

    October 16th, 2010 1:15 pm Reply
  • Sarah, the Healthy Home Economist

    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.

    October 16th, 2010 12:24 pm Reply
  • Sarah, the Healthy Home Economist

    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.

    October 16th, 2010 12:14 pm Reply
    • Carol

      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

      April 17th, 2014 11:04 am Reply
  • Pure Mothers

    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

    October 16th, 2010 8:00 am Reply
  • Janelle Hoxie

    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?

    October 16th, 2010 4:31 am Reply
  • Cheeseslave

    Another great post – thanks, Sarah!

    October 16th, 2010 3:33 am Reply
  • Sarah, the Healthy Home Economist

    Hi Natasha, I my fave is Ohsawa brand Organic Unpasteurized Soy Sauce. Thanks for reading!

    October 15th, 2010 8:48 pm Reply
  • Natasha @ Saved by the Egg Timer

    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!

    October 15th, 2010 8:44 pm Reply

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