Soy, Thyroid and You!

January 11, 2017

I’m asked this question a lot: Can I eat soy if I take thyroid medication to regulate its function. So I put on my reading glasses and scoured the net for reliable sources of information to put together for you so you can understand the impact of soy on your health and wellness.


It’s mostly good news!


But before we get into all of that, let’s figure out what our thyroid is and does first, shall we? The thyroid is a small butterfly-shaped gland located at the front of your neck. This tiny gland has a mighty job. It produces tetraiodothyronine (T4) and triiodothyronine (T3), which are two primary hormones that control how your cells use energy. Your thyroid gland regulates your metabolism through the release of these hormones.


Hyperthyroidism occurs when the thyroid produces too much of these hormones. High amounts of T4, T3 or both can cause an excessively high metabolic rate. This is called a hypermetabolic state where you may experience a rapid heart rate, elevated blood pressure, and hand tremors. You may also sweat a lot and develop a low tolerance for heat. Hyperthyroidism can cause more frequent bowel movements, weight loss, and in women, irregular menstrual cycles.


Visibly, the thyroid gland itself can swell into a goiter, which can be either symmetrical or one-sided. Your eyes may also appear quite prominent, which is a sign of exophthalmos, a condition that’s related to Graves’ disease.


Hypothyroidism is the result of an underactive thyroid and can result in symptoms like fatigue, sensitivity to cold, weight gain, depression, muscle weakness, elevated cholesterol levels, thinning hair and irregular, but heavy-flow menstrual cycles, as well as slowed heart rate and loss of memory.




Okay, now that we know what the thyroid does, what is the controversy with soy?


You should know this debate has been ongoing for more than a decade and there is still disagreement as to soy and thyroid health. But in all my research I have discovered a good bit that makes me feel more comfortable saying that in most cases, people with thyroid issues may enjoy some soy and there’s no reason for people without thyroid issues to avoid it.


Soybeans have been a source of food…and medicine in Asia for more than 5000 years in the form of tofu, tempeh, miso, soy sauce, natto and edamame. It was considered an important food source and with good reason.


Modern science shows us that soybeans contain a plethora of nutrients including a series of compounds called phytochemicals (common in all plants). Unique to soy, however, are phytoestrogens, whose weak estrogenic effects can be effective in helping us feel hormonally balanced as they behave in the body as do estrogen receptor cells.


Regardless of what experts think of soy’s overall health benefits, our concern here is how these foods can affect the thyroid and its function.


There has been some concern that soy may have negative effects on thyroid function and hormonal health because it falls into a category of foods known as goitrogens (vegetables, grains and foods that promote formation of goiter or an enlarged thyroid). Some goitrogens also have a definite anti-thyroid effect and appear to be able to slow thyroid function, and in some cases, trigger thyroid disease.


However, recent studies have shown that in order for soy to adversely affect the thyroid, other factors have to be present like iodine deficiency, problems with hormone synthesis or additional goitrogens in the diet.


Andrew Weil, MD, while usually a proponent of soy, has some thyroid-related concerns about soy. He has said at his “Ask Dr. Weil” website:


“Excess consumption of soy can affect thyroid function, if you have a thyroid disorder to begin with or if you’re not getting enough iodine in your diet…you’re unlikely to get too many isoflavones as a result of adding soy foods to your diet — but you probably will take in too much if you take soy supplements in pill form. At this point, I can only recommend that you avoid soy supplements entirely.”


The issue of genetically modified soy is also controversial and a concern, as the corporations that are farming soy claim that genetically modified organisms (GMO) in foods, including soy,  are safe, while experts on the holistic side of healing say otherwise (me included…).


In 2006, the medical journal, Thyroid, published findings that revealed that soy foods…in the form of real foods, like tofu and tempeh and not the processed versions of soy, like isolated soy proteins were, in fact healthy for people, including some with thyroid conditions if they had enough iodine in their diets.


That could explain the use of soy in Asia, seemingly without problems. One of the biggest differences in diet between Asia and America is the use of sea vegetables in cooking. Rich sources of iodine, sea veggies play a small, but important role in Asian cooking and could be the reason there are fewer issues with soy as sea vegetables contain iodine. Another factor in Asian use of soy is that they keep their consumption to 20-30 mg of isoflavones from soy per day. In typical American fashion, our average consumption of soy isoflavones exceeds 80 mg daily because so many processed products contain it, from protein bars and powders; soy milk, soy nuts, cereals enriched with soy and soy supplements.


In the end, the NIH conducted a study that found little concern with soy and thyroid (see the abstract at the end of this article), but that if you have a thyroid condition, be sure that you have adequate iodine in your diet; that you choose only whole unprocessed soy foods, meaning traditional soy, like tofu, tempeh, miso, natural soy sauce, natto and edamame and that you limit your intake to a couple of servings per week.


I’m going away from research now to give you my humble opinion, based on years of experience and research and my understanding of Traditional Chinese Medicine. I think that organic, unprocessed soy products are safe for most people. For those with thyroid issues, I have seen people successfully bring soy back into their diets with sea vegetables or by simply taking a kelp supplement to ensure that they have adequate iodine levels in their bodies. In my view, organic traditional soy foods are invaluable to us in so many ways as sources of protein and other valuable nutrients.


I also believe that people over-eat soy and not only because it’s versatile and takes on any flavors a cook might desire. Soy foods are easy to cook, quick to cook and so I believe that people rely on them to create quick meals because they have so little time to spend in the kitchen.


I would advise that we use soy products a little more judiciously; a couple of servings a week of tofu, tempeh or edamame and that we rely on other sources of plant proteins to fill in the gaps. Beans cook relatively quickly and if your time is seriously short, you can always use canned, organic beans instead.


In the end, traditional soy products will remain valuable foods for us as long as we keep things in perspective and use them wisely in our cooking.


NIH Abstract

Soy foods are a traditional staple of Asian diets but because of their purported health benefits they have become popular in recent years among non-Asians, especially postmenopausal women. There are many bioactive soybean components that may contribute to the hypothesized health benefits of soy but most attention has focused on the isoflavones, which have both hormonal and nonhormonal properties. However, despite the possible benefits concerns have been expressed that soy may be contraindicated for some subsets of the population. One concern is that soy may adversely affect thyroid function and interfere with the absorption of synthetic thyroid hormone. Thus, the purpose of this review is to evaluate the relevant literature and provide the clinician guidance for advising their patients about the effects of soy on thyroid function. In total, 14 trials (thyroid function was not the primary health outcome in any trial) were identified in which the effects of soy foods or isoflavones on at least one measure of thyroid function was assessed in presumably healthy subjects; eight involved women only, four involved men, and two both men and women. With only one exception, either no effects or only very modest changes were noted in these trials. Thus, collectively the findings provide little evidence that in euthyroid, iodine-replete individuals, soy foods, or isoflavones adversely affect thyroid function. In contrast, some evidence suggests that soy foods, by inhibiting absorption, may increase the dose of thyroid hormone required by hypothyroid patients. However, hypothyroid adults need not avoid soy foods. In addition, there remains a theoretical concern based on in vitro and animal data that in individuals with compromised thyroid function and/or whose iodine intake is marginal soy foods may increase risk of developing clinical hypothyroidism. Therefore, it is important for soy food consumers to make sure their intake of iodine is adequate.


Read the whole study here: