It’s been awhile since I’ve written an article on goitrogens, and so I figured I’d put together a blog post discussing 5 different things you should know with regards to goitrogenic foods. For those reading this who are unfamiliar with goitrogenic foods, there are certain foods that can potentially suppress the function of the thyroid gland, and it accomplishes this by interfering with the uptake of iodine. This in turn can result in the formation of a goiter, which is an enlargement of the thyroid gland. There are also “environmental goitrogens”, which are certain substances or chemicals that can inhibit the production of thyroid hormone, although the focus of this blog post will be on foods. According to the literature, the following foods have been identified as being goitrogenic (1):
- Broccoli
- Brussels sprouts
- Cabbage
- Cauliflower
- Mustard greens
- Radishes
- Millet
- Spinach
- Cassava
- Peanuts
- Soybeans
- Strawberries
- Sweet potatoes
- Peaches
- Pears
- Green tea
So now that you are aware of some of the more common goitrogenic foods, let’s go ahead and discuss five things you need to know about them.
1. There are no human studies showing that cruciferous vegetables can cause a goiter. It’s very common for people with hypothyroidism or Hashimoto’s to express concern about eating cruciferous vegetables such as broccoli, kale, and cauliflower. However, these are very healthy foods, and while some people with hypothyroidism might have problems eating cruciferous vegetables, this isn’t common. Although there aren’t any human studies which demonstrate that eating cruciferous vegetables can inhibit thyroid hormone production, there are rat studies which show the goitrogenic effects of cruciferous vegetables.
One study showed that cabbage can significantly reduce plasma thyroxine (T4) levels within days, even when consuming a moderate amount of iodine (2). One thing I need to say is that cooking foods can decrease the goitrogenic properties, although you of course don’t want to cook cruciferous vegetables for too long in order to avoid the loss of nutrients.
2. Drinking high amounts of green tea might have a goitrogenic effect. A few studies have looked at the goitrogenic effect of green tea extract in rats, and found that catechin present in green tea extract might have antithyroid activity, and that drinking green tea at high doses can alter thyroid function adversely (3) (4). Keep in mind that the study specifically said that drinking “high doses” of green tea can have adverse effects on thyroid function, which perhaps explains why I haven’t seen a problem with my patients drinking green tea. And so I’m not suggesting for those with thyroid and autoimmune thyroid conditions to completely avoid drinking green tea. Plus, remember that just as is the case with cruciferous vegetables, these studies were conducted on rats, and not humans.
3. Not all goitrogenic foods are created equally. Some foods are considered to be more goitrogenic than others. For example, cruciferous vegetables are supposedly more goitrogenic than other foods such as spinach, strawberries, and peaches. Soy is perhaps the most goitrogenic food, but this isn’t the only reason why I recommend for my patients to avoid soy. As I discussed in a blog post entitled “4 Reasons Why Soy Should Be Avoided In Those With Thyroid Conditions“, soy is a common allergen, soy has phytates, which can lead to a decrease in iron and calcium absorption, and most soy is genetically modified. Although there are health benefits of eating organic fermented soy, the fermentation process apparently doesn’t reduce the goitrogenic properties.
4. A moderate to severe iodine deficiency can make goitrogenic foods more problematic. As I mentioned in the opening paragraph, the way that goitrogenic foods can potentially inhibit thyroid hormone production is by interfering with iodine uptake. So not surprisingly, those people who have a moderate or severe iodine deficiency are more likely to have problems when eating raw goitrogenic foods. While it might be a good idea to test for an iodine deficiency, keep in mind that not everyone with thyroid and autoimmune thyroid conditions do well when supplementing with iodine, and there is some evidence of this in the comments section of a blog post I released in 2016. This doesn’t mean that an iodine deficiency shouldn’t eventually be addressed, but in many cases it makes sense to improve the health of the immune system before addressing an iodine deficiency, which I discussed in an article I wrote entitled “An Update On Iodine and Thyroid Health”.
5. Turmeric can benefit those who eat a lot of goitrogenic foods. I absolutely love turmeric, as it has many health benefits. And one study involving 2335 residents of Pakistan showed that turmeric can help to reduce goiters (5). 669 of these subjects had a palpable goiter, and most were either hyperthyroid or euthyroid (had normal thyroid hormone levels). The authors recommended that those who eat high goitrogenic diets should be educated to consume turmeric to reduce the risk of goiter development. Keep in mind that turmeric isn’t well absorbed, which is why many turmeric supplements add piperine, liposomes, or other substances to help increase turmeric absorption.
So hopefully you learned a few things about goitrogenic foods. What I want you to take away from this blog post is that most people with thyroid and autoimmune thyroid conditions can eat a few servings of cruciferous vegetables per day, and most of the other foods listed above can also be safely eaten, with the possible exception of soy, peanuts, and millet. It’s also important to understand that since goitrogens interfere with iodine uptake, having a moderate to severe iodine deficiency can make someone more susceptible to the goitrogenic effects of certain foods. It’s also useful to know that turmeric can help to reduce goiter formation, and while fermentation doesn’t seem to reduce the goitrogenic properties of soy, cooking cruciferous vegetables can decrease the goitrogenic activity.
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