Thyroid-Friendly Eating: What You Need to Know About Goitrogenic Foods

Sufficient iodine in our diet plays a crucial role in good health, iodine is a critical mineral our body needs to create thyroid hormones. These hormones control the body's metabolism and are essential for numerous other functions in the body. An excess or lack of iodine can cause hyperthyroidism or hypothyroidism the latter of which can lead to a range of detrimental effects and goitre, a condition where the thyroid gland becomes enlarged in attempts to absorb more iodine and presents as a visible swelling in the neck.

To reduce the risk of developing goiter a public health initiative was established which resulted in salt manufacturers adding iodine to table salt in the 1920s. This addition ensured that most people in the industrialised world are easily able to consume more than enough iodine.

However, as popularity of foods like kale, broccoli and cruciferous vegetables has increase in recent times due to being promoted as so called “super foods” due to their ability to promote and support health, there has been concern about foods classified as “goitrogens.”  which can interfere with the thyroid’s ability to utilise iodine and, could cause goiters in people who consume too much of them.

Goitrogens are just one type of so-called “antinutrient” that can block the body’s uptake and use of nutrients. Other antinutrients you might be more familiar with include phytoestrogens, lectins, and phytates.

But while this quality of goitrogens can sound alarming, the truth is that their impact on thyroid health is not clear. Some studies suggest that foods containing these substances may have both positive and negative effects.

Taking this into consideration we must wonder if you should you be concerned about their impact on your health? And do the amounts in food warrant fear or avoidance? To better understand this let’s look at Goitrogens in more detail.

What Are Goitrogens?

As we’ve seen, goitrogens are compounds that can interfere with thyroid function and could potentially promote enlargement of the thyroid gland (known as a goiter). Dietary goitrogens were discovered in 1928 when researchers studying syphilis in rabbits accidentally caused goiters in some of their subjects by feeding them nothing but cabbage.

Goitrogens aren’t just found in foods, however. They can also exist in pharmaceuticals and in chemicals in the environment. Drugs that contain goitrogens include phenazone, lithium, sulfadiazine, and cycloheximide.

There are also environmental chemicals that can inhibit iodine absorption. These include polychlorinated (PCB) and polybrominated (PBB) biphenyls, both of which are common in a variety of industries. PCBs are used in circuit boards, which are pretty much everywhere these days, as well as in many other industries. And PBBs were popular flame retardants used for decades in plastics and appliances and still linger in the environment despite having mostly been phased out of use.

You may also be exposed to environmental goitrogens via certain pesticides, as well as smoke from burned coal, petroleum, and tobacco. If you needed another reason not to smoke, or to avoid second-hand smoke, here it is.

Goitrogens in food include compounds containing sulfur, such as thiocyanate, isothiocyanate, goitrin, disulfides, and some polyphenol flavonoids. 

Are Goitrogens Bad for You?

If you’re already deficient in iodine, you might have depressed thyroid function, and goitrogens in food can make the situation worse. Studies of populations living in areas with insufficient iodine in the soil have shown that goitrogenic foods can exacerbate hypothyroidism.

A 2012 study of women with low iodine intake in New Caledonia, an archipelago in the South Pacific, found that high consumption of cruciferous vegetables (one of the classes of goitrogen-containing foods, as we’ll see below) was associated with increased risk of thyroid cancer.

It makes sense: Goitrogens can reduce the amount of available iodine, so if that amount is already too low for proper thyroid function, decreasing it even more is a recipe for ill health. Not only can goitrogens lead to the development of goiters, but they can also have unpredictable effects on thyroid function, sometimes causing hypothyroidism, and other times causing the thyroid to overcompensate in its production of hormones, leading to hyperthyroidism (overactive thyroid).

If you aren’t getting enough iodine, the first thing to do is to work with a health care practitioner to correct that deficiency. Adding a source of absorbable iodine can help counter the effects of goitrogens by supporting your thyroid in its ability to synthesize hormones.

Goitrogens and Hypothyroidism

Animal studies suggest that excessive consumption of goitrogenic foods may disrupt thyroid function and contribute to the development of hypothyroidism.

A 2015 Iraqi study of rabbits found that a month of nothing but cruciferous vegetables there was a significant decline in the fertility of both males and females compared to a control group fed a normal diet and an experimental group that was fed non-cruciferous fare one day out of three. The cruciferous-only group didn’t produce any offspring, unlike the other groups.

It is not always a straight forward process to extrapolate animal studies to draw a precise conclusion in respect to humans, however based on the studies it seems sensible that people with hypothyroidism, including Hashimoto’s thyroiditis (an autoimmune disorder), may want to limit their intake of goitrogenic foods in order to optimise their thyroid hormone levels.

Goitrogens, Iodine, and Hyperthyroidism

What about someone with hyperthyroidism? Are goitrogens helpful in taming an overactive thyroid? There are lots of factors that can influence how someone with hyperthyroidism will respond to goitrogenic foods. They include the severity and underlying cause of hyperthyroidism, individual variations in thyroid function, and dietary iodine levels.

For example, excessively high iodine intakes have been reported in people who regularly consume certain kinds of seaweed. Getting too much iodine may lead to elevated Thyroid Stimulating Hormone (TSH) levels and to iodine-induced hyperthyroidism. Here’s some potentially good news, Goitrogenic foods may also protect people with hyperthyroidism against the overproduction of thyroid hormones. By inhibiting the thyroid’s ability to produce excessive amounts of these hormones, goitrogens may potentially alleviate symptoms of hyperthyroidism.

What Foods Are Goitrogenic?

The main foods we hear about that contain goitrogens are cruciferous vegetables and soy, however there are also a number of lesser known goitrogenic foods.

To help you manage your consumption below is a fairly comprehensive list of goitrogenic foods.

Cabbage

Kale

Cauliflower

Broccoli

Turnips

Brussels sprouts

Bok choy

Soybeans and soy products

Millet

Cassava

Lima beans

Flaxseed

Sorghum

Sweet potato

The conundrum is that many of the foods in the list above have a number of significant proven health benefits as part of a balanced diet. Cruciferous vegetables, in particular, have been shown to provide many disease-fighting health benefits. Members of the cruciferous family show powerful antioxidant, anti-inflammatory, and neuroprotective effects on the human body — in part because of their glucoraphanin, the precursor to sulforaphane. And foods considered to be goitrogenic also contain thousands of other bioactive compounds that may be protective against numerous chronic diseases.

Iodine isn’t the only nutrient that affects your thyroid health. Not getting enough iron, vitamin A, and selenium can also lead to goitrogenic effects on the thyroid. And many of the foods that contain goitrogens are also good sources of these nutrients.

A Few Words About Soy

Soy-based foods may hinder the absorption of thyroid hormone replacement medication. For this reason, some health care professionals advise patients with hypothyroidism to take their thyroid medication on an empty stomach, or at least not alongside a meal containing soy.

There is also some concern that the consumption of isoflavones, which are potent compounds found in soy, may increase the risk of hypothyroidism in women with low iodine intake. Therefore, if you’re concerned about hypothyroidism, you may want to consider removing soy and products containing soy form your diet.

How to Reduce Goitrogens in Food

You can reduce your dietary intake of goitrogens while still getting the health benefits of the foods that contain them. One strategy is to vary your diet and avoid excessive consumption of any particular food or food group. Hyper-focusing on any food group to the exclusion of other foods can cause vitamin and mineral deficiencies, as well as an overdose of compounds like goitrogens.

Another strategy is to soak goitrogenic foods like soybeans, millet, and lima beans before cooking them. Soaking can reduce antinutrient compounds like goitrogens by removing the ones that are water soluble, or by deactivating enzyme inhibitors. After soaking, make sure to pour off the water, which may retain those goitrogenic compounds. In addition, cooking foods high in goitrogens greatly reduces any possible negative effect on your thyroid gland.  Steaming and boiling, in particular, decreases goitrogenic compounds in food by up to 80%.

In Conclusion

It evident that Goitrogen compounds found in certain foods that can impact iodine absorption and impact the function of the thyroid gland. For most people, there is no need to worry about the effects of goitrogens on their health, since the levels of goitrogens in most foods are not in quantities high enough to cause any significant harm if eaten in moderation. You can take further steps to mitigate risk of harm by eating a balanced diet, as well as soaking and cooking certain goitrogenic foods before eating.

People with preexisting thyroid conditions, such as hypothyroidism or iodine deficiency, may need to moderate or eliminate their consumption of goitrogenic foods. In general, though, if consumed by people who are healthy and do not have metabolic or thyroid related diseases foods which contain goitrogens can have health promoting effects and are not harmful if consumed in in moderation in normal, daily serving sizes.