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