Soy is definitely one of the more controversial foods with regards to digestive, thyroid and hormonal health.

In my practice soy is often eliminated from a client’s diet for many reasons including the fact that it is a listed allergen,  it is often genetically modified, has been shown to suppress thyroid function and can contribute to hormonal imbalance body.

While I agree there are some health benefits of eating organic, fermented soy, too much soy can come with negative health effects.

Let’s take a  closer look at soy…

Soy can be both an allergen and a food sensitivity for many people.  If someone has an allergy to soy, most likely they will have an immediate immune reaction perhaps in the form of breathing difficulties, rash, swelling etc.   A sensitivity on the other hand is known as a delay immune reaction.  What this means is that after ingestion of soy, symptoms may not develop for hours or days!  In fact, blood testing can actually determine whether you have an IgE-mediated soy allergy or an IgG-mediated soy sensitivity.  For more information on Food sensitivity testing click here.    What’s wrong with continuing to eat soy if you have an allergy or sensitivity? The problem with eating ANY food that you have an allergy or sensitivity to is that this will result in inflammation, joint pain, weight gain, constipation or skin issues (just to name a few).

Genetically modified soy also comes with it’s own set of concerns.  Genetically modified foods contain something called glycophosphates (the key ingredient in Monsanto’s RoundUp weedkiller, which the majority of Monsanto’s seeds are genetically engineered to withstand). The weed killer has been blamed for super weeds, found in our streams, soil, air, rainwater, and groundwater and it also affects our digestive system by inhibiting critical enzymes which manifests slowly over time, as inflammation and damages the gut microbiome.  Of course, there are many more articles on why genetically modified foods should be avoided.  For more information click here.

The potential effects of soy on the thyroid  still remains a controversial issue.  Various experts and organizations, including the Weston Price Foundation, are vocally opposed to soy. Soy falls into a category of foods known as goitrogens — foods that promote formation of goiter  along with having anti-thyroid effect which appears to  slow thyroid function, and in some cases, trigger thyroid disease.    I suppose if  you do not have a thyroid gland due to surgery or you have a totally non-functioning gland (due to radioactive iodine ablation treatment), soy will not interfere with your thyroid but it may still interfere with absorption of your thyroid hormone replacement medication, so be sure to take your medication at least three hours apart from soy foods. Kaayla Daniels, Ph.D., author of The Whole Soy Story, suggests that the thyroid-toxic effects of soy are most often seen at levels above 30 mg of soy per day.  She also points out thousands of studies linking soy to malnutrition, digestive distress, immune-system breakdown, thyroid dysfunction, cognitive decline, reproductive disorders and infertility—even cancer and heart disease.  The Food and Drug Administration (FDA) concluded in 1999 that 25 g/d of soy protein as part of a diet low in saturated fat may reduce risk of coronary heart disease.

Having said all that, I want to be clear that I am not opposed to all soy. Soy can be incredibly healthful, but ONLY if it is organic and properly fermented.  The fermentation process decreases the phytates (which bind to minerals)  and “anti-nutrient” levels, making the beneficial properties become available to your digestive system.  I do still believe it best to avoid industrially processed, soy protein ingredients, such as soy protein isolate, textured vegetable protein, hydrolyzed soy protein  widely used in protein powders and shakes, energy bars, veggie burgers and low-fat versions of soy milk.

The primary fermented soy products you’ll find in the grocery stores or health food stores are:

  • Tempeh – A fermented soybean cake with a firm texture and nutty, like flavor.  Tempeh absorbs other flavors and can be purchased unflavored or flavored. It can be used in chili, stir-frys, soups, salads, sandwiches, stews and in wraps (my favorite).
  • Miso – A salty paste made from fermented beans (usually soybeans, but also barley and rice) that has been a staple ingredient in the Japanese diet for thousands of years. Another benefit of miso is that it’s brimming with probiotics.  Make sure to purchase organic, fermented and unpasturizeded miso found in the refrigerator section of the store.  This type of miso is filled with beneficial, live probiotic cultures so it is best not to cook with it but use it as a dressing (recipes below) or add it at the end of the cooking process when making soups.
  • Natto – A traditional food usually consumed at Japanese breakfast tables together with rice.  Natto is known to be a rather acquired taste, due to it’s strong smell and gooey, stringy texture.  One of the main reasons natto is so good for you is because it is rich in vitamin K2 which benefits the heart and has been shown to help prevent hardening of your arteries.  You most likely won’t find this in your local store but perhaps in a Japanese grocery store.

Sorry, tofu is NOT on this list. Tofu is not fermented although sprouted tofu is now available.  The sprouting process makes it easier to digest by releasing the phytates that would normally block mineral absorption and cause digestive distress.

The Takeaway? Eating fermented soy does have it’s health benefits and is a great plant based protein if you are looking to cut back on animal proteins (meats, fish, eggs etc.)  For healthy adults, I believe moderation is key and that consuming soy once or twice a week to be safe.


Miso dressing



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