Soy is definitely one of the more controversial foods with regards to thyroid health. While there are some health benefits of eating organic, fermented soy, there are also some negative health effects that soy can have. In this blog post I’m going to discuss four reasons why people with thyroid and autoimmune thyroid conditions should consider avoiding soy while restoring their health.
1. Many people have soy allergies and sensitivities. The Food and Agriculture Organization of the United Nations includes soy in its list of the 8 most significant food allergens, and at least 16 potential soy protein allergens have been identified (1) . There is evidence that approximately 50% of children with a soy allergy outgrew their allergy by age 7 years (2) . But of course this means that 50% don’t outgrow the allergy. Plus, many people don’t have IgE-mediated soy allergies, but instead have an IgG-mediated soy sensitivity.
But what’s the difference between a soy allergy and a sensitivity to soy? I’m not going to get into detail about this here, as if you’d like more information you can read an article I wrote entitled “Food Allergies, Sensitivities, and Thyroid Health “. But essentially a soy allergy involves an immediate reaction, whereas a soy sensitivity involves a delayed reaction. In other words, if someone has a soy allergy they typically will have a negative reaction within a few minutes of consuming soy. On the other hand, if someone has a soy sensitivity they might not have a negative reaction for a few hours, or perhaps even a few days after consuming soy.
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. This in turn can interfere with the healing process. And while you can run a food allergy or food sensitivity panel to determine if you react to soy, these tests aren’t completely accurate.
2. Most soy is genetically modified. Unfortunately most of the soy is genetically modified. Some actually think this is a good thing, and there are a few studies which suggest that genetically modified soy might be less allergenic than non-GMO soy (3)  (4) . But the problems with GMOs doesn’t just relate to allergies. One of the main concerns is that genetically modified soybeans contain high residues of glyphosate.
I spoke about glyphosate in greater detail in an article entitled “Does Glyphosate Have a Negative Effect on Thyroid Health? “. Glyphosate is the active ingredient in the herbicide Roundup, and while it can have an adverse effect on our health in numerous ways, one of the main problems is that it can have a negative effect on our gut microbiota. This gut dysbiosis can make someone more susceptible to developing an autoimmune condition such as Graves’ Disease and Hashimoto’s Thyroiditis.
3. Soy has goitrogenic properties. Goitrogens are substances which inhibit thyroid function. And a few studies have shown that soy has goitrogenic effects (5)  (6)  (7) . One of these studies demonstrated that the effect on the thyroid hormones was minimal, although the study involved short-term soy consumption, lasting only seven consecutive days. On the other hand, another study involving soy supplementation for eight weeks in those with subclinical hypothyroidism showed that there is a 3-fold increased risk of developing overt hypothyroidism, although soy also helped to decrease insulin resistance, inflammation, and blood pressure (8) .
Should other goitrogenic foods be avoided as well, such as cruciferous vegetables? I usually don’t recommend for my patients with hypothyroidism and Hashimoto’s Thyroiditis to avoid cruciferous vegetables. After all, foods such as broccoli, kale, cabbage, and cauliflower have numerous health benefits, and I think that most people should be eating these foods on a daily basis. I’m not suggesting for people to eat four or five cups of raw cruciferous vegetables per day, but having one or two servings of these foods usually won’t cause any problems from a goitrogenic standpoint.
4. Soy has phytates. Phytic acid is an anti-nutrient that is found in grains, nuts, seeds, and legumes, including soybeans. And studies show that the phytates in soy can lead to a decrease in iron and calcium absorption (9)  (10) . The good news is that soaking and fermenting soy can significantly decrease the levels of phytic acid.
Should You Be Concerned About the Estrogenic Properties of Soy?
Isoflavones are a type of phytoestrogen found mostly in soy products, and there is some controversy over whether phytoestrogens can be harmful to our health. I wrote an article on this entitled “The Truth About Soy, Flaxseed, And Other Phytoestrogens “. While some consider soy as being an endocrine disruptor, the research I have found doesn’t show this, and there are actually numerous benefits to phytoestrogens. However, I will admit that I try to avoid soy as much as I can, and most of the phytoestrogens I get are from other sources, such as flaxseed.
In summary, soy should be avoided in those with thyroid and autoimmune thyroid conditions. While there are some health benefits of eating organic, fermented soy, many people have soy allergies and sensitivities. In addition, soy has goitrogenic properties, and it also has phytates, which can interfere with the absorption of nutrients. As a result, I usually recommend for my patients to avoid eating soy.