Goitrogens, Thyroid Disease, and Your Diet

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, 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.

Some Foods Containing Goitrins and/or Thiocyanates

• 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
• Sweet potato
• Turnips
• Watercress

Some Foods Containing Flavonoids

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

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 is incorporated into 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.

In very large quantities, goitrogens can cause a goiter or 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 take thyroid medication on an empty stomach. It's not necessary to completely avoid soy foods.

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.

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:

• Moderation: Avoid consuming extremely large quantities of goitrogenic foods. Consuming a moderate amount is actually very healthy since they are rich in nutrients. Problems almost never occur, and only when they are consumed in extremely large quantities.
• 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 mostly eat cooked goitrogens and have a difficult time balancing your thyroid treatment, you may want to consider cutting back on the overall amount of goitrogenic foods in your diet.

Thyroid Conditions That Are Unaffected by Goitrogens

Not everyone with a thyroid condition needs to be aware of goitrogens.

You don’t need to be particular about goitrogens if you are hypothyroid due to:

• Thyroidectomy—a surgical procedure done to treat thyroid cancer or to remove a goiter or nodules
• Radioactive iodine (RAI) treatment for Graves' disease

Thyroid tissue that has been destroyed by these procedures is not susceptible to goitrogenic effects.

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