Goitrogens, Thyroid Disease, and Your Diet

Cruciferous vegetables and other foods can affect your thyroid

Close up of woman chopping vegetables
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Goitrogens are naturally-occurring chemicals found in many plant-based foods. Consuming high amounts of these substances on a regular basis may have an impact on your thyroid health, so it's worth understanding how they affect thyroid function and whether or not it makes sense to limit your intake of goitrogenic foods such as broccoli, cauliflower, kale, strawberries, and others.

Common Goitrogenic Foods

The key goitrogen-rich foods are vegetables in the cruciferous category; some fruits, nuts and grains also contain these substances.

There are three types of goitrogens: goitrins, thiocyanates, and flavonoids.

Foods that contain goitrins and/or thiocyanates include:

  • African cassava
  • Babassu (a palm-tree coconut fruit found in Brazil and Africa)
  • Bok choy
  • Broccoli
  • Broccolini
  • Brussels sprouts
  • Cabbage
  • Canola
  • Cauliflower
  • Chinese Broccoli
  • Collards
  • Daikon
  • Flax
  • Kale
  • Kohlrabi
  • Millet
  • Mustard
  • Peaches
  • Peanuts
  • Pine nuts
  • Radishes
  • Red Radish
  • Rutabaga
  • Spinach
  • Strawberries
  • Sweet potato
  • Turnips
  • Watercress

Some foods containing flavonoids include:

  • Berries
  • Red wine
  • Soy products such as tofu, tempeh, edamame, and soy milk
  • Teas, especially green, white, and oolong varieties

Goitrins and thiocyanates are released from certain plant-based foods when they are sliced or chewed in their raw state. Flavonoids in foods can be also be converted into goitrogenic compounds by bacteria that exist in the gut.

How Goitrogens Can Affect the Thyroid

Foods that contain goitrogens are able to disrupt thyroid function by inhibiting your body’s ability to use iodine. More specifically, goitrogens can block the process by which iodine becomes the key thyroid hormones thyroxine (T4) and triiodothyronine (T3).

They also inhibit the actual release of thyroid hormone by your thyroid gland and disrupt the peripheral conversion of the thyroid storage hormone T4 into the active thyroid hormone T3.

As a result, goitrogens can cause a goiter, an enlarged thyroid. They can also act like antithyroid drugs, slowing down your underactive thyroid and potentially causing hypothyroidism.

A Word About Soy

While soy foods do not affect the thyroid gland in people with normal thyroid function and adequate iodine levels, they can interfere with the absorption of thyroid hormone replacement medication. This is why experts recommend that patients with hypothyroidism don't necessarily avoid soy foods, but make sure to take their thyroid medication on an empty stomach.

In some cases, the dosage of a person's thyroid medication will need to be adjusted if soy is regularly consumed.

There is also some concern that consuming isoflavones, the active ingredients in soy, may trigger the transformation from subclinical to overt hypothyroidism in people with marginal iodine intake. Research regarding this phenomenon is controversial, however.

Soy and Thyroid Health: What You Need to Know

Minimizing the Effects of Goitrogenic Foods

Goitrogenic foods are rich in vitamins and minerals, and most experts do not recommend that anyone—including patients with thyroid disease—avoid eating them. However, there are a few sensible guidelines to consider if you have an underactive thyroid or are worried about goitrogens in your diet.

Here's what you can do to minimize the risk of negative effects:

  • Cook goitrogenic vegetables: Steaming, cooking, or fermenting can reduce the levels of goitrogens. If you like fresh spinach or kale in smoothies, try blanching the veggies and then storing them in the freezer for later use.
  • Increase your iodine and selenium intake: Getting enough iodine and selenium can help reduce the effects of goitrogens; iodine deficiency is a well-known risk factor for thyroid dysfunction, though it is rare for people living in the United States to be deficient. Good dietary sources of iodine include seaweed—such as kelp, kombu, or nori—and iodized salt. (Less than half a teaspoon of iodized salt covers your daily iodine requirement.) Great sources of selenium include Brazil nuts, fish, meat, sunflower seeds, tofu, baked beans, Portobello mushrooms, whole grain pasta, and cheese.
  • Switch it up: Eating a variety of foods—non-goitrogenic as well as goitrogenic—will help limit the amount of goitrogens you consume and ensure that you get a healthy assortment of vitamins and minerals.

    If you are hypothyroid and still have a partially functional thyroid—such as with Hashimoto's thyroiditis—be especially careful not to overconsume large quantities of raw goitrogenic foods.

    If you mostly eat cooked goitrogens and have a difficult time balancing your thyroid treatment, you may want to consider cutting back on the amount of goitrogenic foods in your diet overall. You should also check with your doctor to make sure your iodine level is sufficient.

    Not everyone with a thyroid condition needs to be aware of goitrogens, however. If you are hypothyroid due to thyroid surgery known as thyroidectomy—a procedure done to treat thyroid cancer or to remove a goiter or nodules—you don’t need to be particular about goitrogens; likewise if you are hypothyroid after radioactive iodine (RAI) treatment for Graves' disease. Thyroid tissue that has been destroyed by these procedures is not susceptible to goitrogenic effects.

    Should I Take a Dietary Supplement if I Have a Thyroid Disorder?

    A Word From Verywell

    Like most things in life, when it comes to diet and your thyroid, moderation is your best strategy. Most foods that contain goitrogens are very nutritious, and the benefits of eating them largely outweigh the risks. If you have adequate levels of iodine in your diet, your thyroid can generally manage a diet that includes goitrogenic foods.

    If you are concerned, or want to make sure your diet is well-rounded, consider consulting with a nutritionist.

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