Getting enough iodine is a big deal when it comes to your health. In adults, too little or too much iodine intake can lead to either hypothyroidism or hyperthyroidism, respectively, causing a cascade of unpleasant symptoms. Iodine deficiency can also cause goiter, an enlargement of the thyroid gland that presents as a visible swelling in the neck, making it hard to swallow and breathe.
But thanks to a public health initiative, salt manufacturers began adding iodine to table salt in the 1920s. And now, most people in the industrialized world are easily able to consume more than enough iodine.
However, lately, there’s been a lot of online chatter about a category of foods classified as “goitrogens.” They’re so named because goitrogens may interfere with the thyroid’s ability to utilize iodine and, theoretically, 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 particular 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-cut. Some studies suggest that foods containing these substances may have both positive and negative effects.
So should you be concerned about their impact on your health? And do the amounts in food warrant fear or avoidance? Let’s dive into the world of goitrogens and find out.
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. (Our view on the use of animals in medical research is here.)
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 secondhand smoke, here it is.
Back to food… Goitrogens in food include compounds containing sulfur, such as thiocyanate, isothiocyanate, goitrin, disulfides, and some polyphenol flavonoids. In a bit, we’ll drop the chemical jargon and talk about the actual foods that contain these substances. But first, let’s tackle the big question: Are the goitrogens in food actually a problem if you’re not a syphilitic rabbit who’s being fed nothing but cabbage? (In case you’re wondering why Looney Tunes opted to make the character of Bugs Bunny love carrots instead of cabbage, it probably had nothing to do with goitrogens.)
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).
At this point, you might find yourself getting confused between hypo- and hyperthyroidism. So here’s a quick Greek lesson: “hypo” means “too little” (for example, hypothermia means too little heat), and “hyper” means “too much” (for instance, hyperactive refers to excessively active behavior).
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
The relationship between goitrogens and hypothyroidism isn’t clear. Some animal studies suggest that excessive consumption of goitrogenic foods may disrupt thyroid function and contribute to the development of hypothyroidism — the expected association.
A 2015 Iraqi study of rabbits found that a month of nothing but cruciferous veggies significantly impacted 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.
People aren’t rabbits, but if you’re willing to work hard enough for long enough, you might be able to replicate the animal findings yourself. People who are “extreme eaters” of raw cruciferous veggies (to the order of more than two pounds a day for several months) can induce hypothyroidism.
For example, a 2010 letter to the New England Journal of Medicine shared a case study of an elderly Chinese woman who ate two to three pounds of raw bok choy a day for several months in an attempt to control her diabetes. When her family brought her to the emergency room, the woman had been so lethargic, she had been unable to walk or swallow for the previous three days.
On the other hand, if you aren’t eating four large heads of raw bok choy every day, or subsisting on nothing but cruciferous vegetables, you might be okay. Other research indicates that if you consume goitrogenic foods in typical serving sizes (say, ½–1 cup), the effect is generally insignificant. Those servings provide goitrogenic exposure far lower than is likely to bother your thyroid. If you are getting enough iodine, and don’t already have hypothyroidism, you don’t face much risk of decreased thyroid function.
But people with untreated hypothyroidism, including Hashimoto’s thyroiditis (an autoimmune disorder), may want to limit their intake of goitrogenic foods in order to optimize 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.
[For more on seaweed, and a chart showing how much iodine they contain, see our article on sea vegetables.]
Here’s some potentially good news, though. 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. But these poster children for the suppression of iodine absorption aren’t the only ones.
Here’s a pretty comprehensive list of goitrogenic foods, courtesy of the veritable online bible of endocrine disease, Endotext:
- Brussels sprouts
- Bok choy
- Soybeans and soy products
- Lima beans
- Sweet potato
The problem is, this list includes many of the healthiest foods on the planet. 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 (to the thyroid as well as 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. So even if you have iodine deficiency or hypothyroidism, you may not want to avoid these foods entirely.
A Few Words About Soy
While soy-based foods are thought to have no impact on the thyroid gland in people with normal thyroid function and sufficient levels of iodine, they 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 (and generally very health-promoting) compounds found in soy, may increase the risk of hypothyroidism in women with low iodine intake. However, research on this matter is mixed, with some studies concluding that soy is actually beneficial to thyroid function. So at this point, we don’t know for sure. If you’re concerned about hypothyroidism, you may want to consider discussing this with your health care provider.
[Find out more on the health effects of soy.]
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. Just because cruciferous vegetables are awesome, doesn’t mean you should eat nothing else. 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.
And remember, cooking foods high in goitrogens greatly reduces any possible negative effect on your thyroid gland. Steaming and boiling, in particular, decrease goitrogenic compounds in food by up to 80%.
The Bottom Line On Goitrogens
Goitrogens are 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 high enough to cause any significant harm. You can also avoid 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 their consumption of raw goitrogenic foods. In general, though, they are not harmful if consumed in normal, daily serving sizes.
Tell us in the comments:
Had you previously heard about goitrogens being dangerous? Did you change your eating habits as a result?
What are your favorite goitrogen-containing foods? How much do you eat raw vs cooked?
Is there room to add more healthy variety to your diet? If so, what might you add?
Featured Image: iStock.com/Iryna Kaliukina