Do goitrogenic foods negatively affect thyroid health?

Goitrogens are compounds found naturally in certain plants. Animal studies suggest that these foods may interfere with the absorption of iodine, essential for thyroid function.

Without enough iodine, the pituitary releases thyroid-stimulating hormone (TSH) and promotes the growth of thyroid tissue, which eventually leads to an enlarged glans penis, or goiter. If the goiter grows, it can interfere with the trachea and esophagus and cause coughing or difficulty swallowing and breathing. However, any substance that interferes with thyroid function is a concern for patients with autoimmune thyroid diseases, such as Hashimoto’s thyroiditis and Graves’ disease, who already struggle with thyroid hormone production.

What plants are goitrogenic?
Several animal studies show that the following raw cruciferous vegetables affect iodine intake and thyroid metabolism:

Bamboo shoots

bok choi

brassica seeds

Broccoli

Brussels sprouts

Cabbage

Cassava

Cauliflower

kale

Swede

Mustard and mustard greens

Peaches

radishes

rutabagas

Soy and soy products

Spinach

strawberries

turnips

What does this mean for thyroid patients?
You’ve probably read this list and thought, “Why can’t I eat these foods when they’re supposed to be good for me?” That’s right. After all, many of these foods are high in nutrients essential for good health.

The limited research done so far does not suggest that eating reasonable amounts of these foods inhibits thyroid activity. However, a diet that is highly dependent on goitrogenic foods could negatively affect patients with autoimmune thyroid disorders.

A diet tailored for optimal thyroid function makes more sense, rather than a broad elimination of all these foods. At this point, no human studies confirm that cruciferous vegetables cause impaired thyroid function.

Dr. Joel Fuhrman’s research spanning fifty years does not suggest these are “bad” foods. They may not be the right foods for certain people. He states that “cruciferous vegetables may only be detrimental to thyroid function in cases of iodine deficiency or insufficient iodine intake,” and may not cause any problems if eaten in reasonable amounts.

How much can I eat?
Unfortunately, there is no simple answer to this question as every patient is different. However, within the functional model of care, it is possible to work with your doctor to find out what works best for you.

In general, most patients with thyroid conditions can tolerate one to two servings of goitrogenic raw foods every day without any problems. Others may need to steam their vegetables to reduce goitrogenic activity.

If a patient wants to include soy in their diet, fermented soy is preferable; however, some evidence suggests that soy and soy products may interfere with the absorption of thyroid medications in patients with hypothyroidism. Patients should not rely heavily on soy in their diet, as it is goitrogenic.

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Eating a few servings of these foods daily shouldn’t be a problem, even if you have Hashimoto’s thyroiditis or Graves’ disease. However, they affect iodine metabolism and if you already have an iodine deficiency, your risk increases.

Although cooking these foods can decrease goitrogenic activity, avoid eating too many of these foods. Discuss your concerns with your doctor and work with them to create a diet plan that works best for you.