by Marcelle Pick, OB/GYN NP
- What is a goitrogen?
- What foods contain goitrogens?
- Enjoy your goitrogens with a sprinkling of common sense
My patients with hypothyroidism sometimes ask about stories they’ve heard in the news or seen on-line about the effects of certain foods on their thyroid health. Soy is their most common concern, but broccoli, peanuts, strawberries, kale, and other vegetables are also on this list. The message my patients hear, unfortunately, is that if you have any sort of thyroid dysfunction, you shouldn’t consume these foods — ever. And that’s a shame, because this all-or-nothing approach means that women with thyroid problems remove healthy, nutritious foods from their diet when they really don’t have to.
It’s true that there are certain foods that contain goitrogens, which are compounds that make it more difficult for the thyroid gland to create its hormones. However, the piece of the puzzle that’s missing in the advice to “avoid” this food or that one because it contains a goitrogen is that you can limit or even eliminate the harmful effects of these compounds in so many ways — either by limiting the amount you consume, or by preparing the food in such a way as to break down the goitrogenic compounds. Sometimes eliminating the goitrogen is as simple as steaming your vegetables before you eat them!
So let’s look at what goitrogens are, where they occur in our food, and how we keep them from affecting our thyroid function so we can enjoy our favorite healthy foods without concern for our thyroid health.
What is a goitrogen?
Most goitrogens are naturally-occurring chemicals that are ingested in foods or drugs. These chemicals can interfere with thyroid function in different ways. Some compounds induce antibodies that cross-react with the thyroid gland; others interfere with thyroid peroxidase (TPO), the enzyme responsible for adding iodine during production of thyroid hormones. Either way, the thyroid isn’t able to produce as many of the hormones that are needed for regulating metabolism (see my article on nutrition and thyroid health for more on how this works).
For people with healthy thyroid function, the thyroid simply compensates and makes more of the hormones as they’re called for. But in some people whose thyroid function is already compromised, the thyroid gland may actually grow more cells as it tries to make up for inadequate hormone production, eventually forming a goiter (a swelling or enlargement of the thyroid gland).
What foods contain goitrogens?
You may be surprised by how many common foods contain goitrogenic compounds, but the good news is, in most cases you don’t have to cross them off your grocery list. Let’s take a look at some of them and discuss how you can keep them in your diet, even if you have hypothyroidism.
- Gluten. It may surprise people to see gluten at the top of my list of potential goitrogens, but the truth is that gluten sensitivity contributes to a wide range of autoimmune responses aside from celiac disease (the one for which it’s best known). Gluten sensitivity has been found to go hand-in-hand with autoimmune disorders such as type 1 diabetes, Addison’s disease, Sjögren’s syndrome, rheumatoid arthritis, and autoimmune thyroid disease. I commonly recommend that my patients consider eliminating gluten from their diets, particularly if they already have an autoimmune disorder. If you have autoimmune hypothyroidism, you might want to consider limiting your intake of wheat, barley, and rye, or even going completely gluten-free (we have a lot more to say about this in our article on gluten). I also suggest that women with autoimmune thyroid disease consider screening for celiac disease, because undetected celiac can be one reason that women continue to have hypothyroid symptoms despite higher and higher doses of thyroid replacement hormone.
If you’d like to keep gluten in your diet but you’re concerned about your thyroid, try scaling back on how often you eat it. Be aware that gluten is included in a great many processed foods, so it may help if you look for those varieties that advertise as gluten-free. And instead of having wheat bread or baked goods with your meal, consider substituting gluten-free grains or saving them for the occasional treat. You may find after awhile that you don’t miss gluten nearly as much as you may have thought (but if you find yourself craving bread or pasta, it could be a sign of gluten sensitivity).
- Soy isoflavones. Soy is a very healthy food that has been demonized by various groups, something we discuss in our article on the soy controversy. One legitimate concern these groups raise is the fact that soy does contain goitrogenic compounds, specifically the soy isoflavone genistein. This compound, just like thyroid hormones, accepts iodine molecules from the thyroid peroxidase (TPO), which again, is the enzyme that also transfers iodine to the thyroid hormones. Some researchers have suggested that genistein and similar isoflavones may compete with thyroid hormones for iodine or alternatively may “block” the action of TPO, but recent studies indicate that as long as an individual has sufficient iodine in the diet, soy isoflavones do not adversely impact thyroid function.
“If one begins with poor iodine nutrition, removing goitrogens from one’s diet will not restore iodine nutrition.”
— Dasgupta, P., et al. 2008. Iodine nutrition: Iodine content of iodized salt in the United States. Environ. Sci. Technol., 42 (4), 1315–1323.
Other good news is that the goitrogenic activity of soy isoflavones can be at least partly “turned off” by cooking or fermenting. With soy foods, you may want to favor fermented, cultured, or otherwise “aged” soybean products such as tempeh, soy sauce, miso, and natto. These methods of processing soybeans alter the activity (goitrogenicity) of the phytochemicals they contain. If you do eat whole soybean foods such as edamame or tofu, eat them cooked or steamed.
The goitrogenicity of soy can also be offset by pairing it with products containing iodine. I tell my patients with thyroid problems that if they already eat soy products and wish to continue, they should be sure to include additional iodide in the diet, in the form of seaweed products such as kombu or nori. For people who don’t already use soy regularly, I suggest that they simply continue whatever limited usage they already have and not worry about it too much, as such small amounts aren’t likely to impact the thyroid too greatly — but keep in mind that if you eat processed foods containing certain soy-based additives like soybean oil or hydrolyzed soy protein, they could be a “hidden” source of soy isoflavones that many hypothyroid woman could probably do without!
So unless you have a true soy allergy, I wouldn’t worry too much about every little soybean or soy shake you consume. More importantly, if you do include soy in your diet and have concerns about your thyroid function, it’s worthwhile to have your iodine levels checked by your practitioner, who can (if necessary) offer you supplemental elemental iodide in amounts that are correct for your profile. We also recommend that people with thyroid problems who consume soy regularly include good dietary sources of selenium — and be sure to continue monitoring thyroid hormone levels regularly with their practitioner.
• Isothiocyanates. These compounds are primarily found in cruciferous vegetables, such as cabbage, Brussels sprouts, broccoli, broccolini, cauliflower, mustard greens, kale, turnips, and collards. Isothiocyanates, like soy isoflavones, appear to block TPO, and they may also disrupt signaling across the thyroid’s cell membranes. But no one would argue that these vegetables are bad for you, given that they are filled with vitamins, minerals, antioxidants, and a variety of nutrients we all need (aside from being delicious!). Women with thyroid problems definitely should not avoid them — instead, enjoy them steamed or cooked, as the heat alters the isothiocyanates’ molecular structure and eliminates the goitrogenic effect.
• Are there more? Maybe… Certain “potentially goitrogenic” compounds are also present in small amounts in peanuts, pine nuts, millet, peaches, strawberries, spinach, and cassava root, among others. I tell my patients who are concerned about these foods that unless they’re consuming them in high amounts on a continual basis, they’re not likely to have undue impact on their thyroid health, because the possible goitrogens are present in such minute quantities.
I’d like to emphasize that these foods won’t pose a problem for people with healthy thyroid function, nor will they be harmful when used in moderation by those whose thyroid function is impaired, but excessive use of foods containing goitrogens may trigger or exacerbate a thyroid problem. This is all the more reason to make sure your diet contains a variety of delicious, healthy, whole foods — we weren’t meant to eat the same thing over and over!
Enjoy your goitrogens with a sprinkling of common sense
I’m always dismayed when women are told they have to avoid a healthy food when there isn’t a very good reason for it (a food allergy, for instance). It would be a shame if women with thyroid problems avoided these goitrogenic foods altogether, because most of what I’ve listed above contain beneficial micronutrients and have strong value as healthy foods that support digestive, skeletal, cardiovascular, and immune function. It just doesn’t make sense to deny the rest of our body the benefits of these foods when the threat they pose to our thyroid is so slight and can be eliminated so easily! So I suggest that we all use a little common sense when it comes to goitrogens and our thyroids — steam, cook, or ferment your vegetables to reduce the goitrogenic compounds, rotate your choices so that you’re not eating the same foods every day, and above all,enjoy them as part of a richly varied diet of wholesome foods.