Goitrogens in Foods: Harmful or Harmless?

Surprised Woman Holding Leafy Greens

Surprised Woman Holding Leafy GreensIf you have thyroid problems, you’ve probably heard of goitrogens.

You may even have heard that some foods should be avoided because of them.

But are goitrogens really that bad, and should you try to avoid them?

This article takes a detailed look at goitrogens and their health effects.

What Are Goitrogens?

Goitrogens are compounds that interfere with the normal function of the thyroid gland.

Put simply, they make it more difficult for the thyroid to produce the hormones your body needs for normal metabolic function.

The link between goitrogens and thyroid function was first described in 1928, when scientists observed thyroid gland enlargement in rabbits eating fresh cabbage (1).

This enlargement of the thyroid gland is also known as a goiter, which is where the term goitrogen comes from.

This discovery led to the hypothesis that substances in some vegetables may affect thyroid function when consumed in excess (2).

Since then, several types of goitrogens have been identified, in a variety of foods.

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Bottom Line: Goitrogens are substances found in certain foods. When consumed in excess, they can interfere with the function of the thyroid gland.

Types of Goitrogens Found in Foods

Broccoli

Broccoli

There are three main types of goitrogens (3):

  1. Goitrins
  2. Thiocyanates
  3. Flavonoids

Goitrins and thiocyanates are produced when plants are damaged, such as when they’re sliced or chewed.

Flavonoids are naturally present in a wide variety of foods. Some examples include the resveratrol in red wine and the catechins in green tea.

Flavonoids are generally considered to be healthy antioxidants, but some of them can be converted into goitrogenic compounds by our gut bacteria (3, 4).

Bottom Line: Goitrins, thiocyanates and flavonoids are the three most common types of goitrogens. They are found in many common foods.

Goitrogens May Cause Thyroid Problems

Chef Inspecting Cabbage

Chef Inspecting Cabbage

Goitrogens can cause thyroid problems by:

  • Blocking iodine: Goitrogens may prevent iodine from entering the thyroid gland, which is needed to produce thyroid hormones.
  • Interfering with TPO: The thyroid peroxidase (TPO) enzyme attaches iodine to the amino acid tyrosine, which together form the basis of thyroid hormones.
  • Reducing TSH: Goitrogens may interfere with thyroid stimulating hormone (TSH), which helps the thyroid gland produce hormones.

When the thyroid’s function is disrupted, it has trouble producing the hormones that regulate your metabolism.

This can lead to problems controlling body temperature, heart rate, protein production, calcium levels in the blood and how your body uses fats and carbs.

A healthy thyroid can make up for a decrease in hormone production by simply releasing more TSH, which pushes the thyroid to produce more hormones.

However, a malfunctioning thyroid is not as responsive to TSH. The thyroid compensates by growing more cells, leading to an enlargement known as a goiter.

Goiters can create a feeling of tightness in your throat, coughing, hoarseness and may make breathing and swallowing more challenging (5).

Bottom Line: Goitrogens can reduce the thyroid’s ability to produce the hormones your body needs to function normally. They are more likely to negatively impact people who already have poor thyroid function.

Goitrogens Can Cause Other Health Problems

Sweet- Potatoes

Sweet- Potatoes

Goiters aren’t the only health concerns to consider.

A thyroid that can’t produce enough hormones may cause other health issues, including:

  • Mental decline: In one study, poor thyroid function increased the risk of mental decline and dementia by 81% for people under 75 years of age (6).
  • Heart disease: Poor thyroid function has been linked to a 2–53% higher risk of developing heart disease and an 18–28% higher risk of dying from it (7, 8).
  • Weight gain: During a 3.5-year long study, people with poor thyroid function gained up to 5 lbs (2.3 kg) more weight (9).
  • Obesity: Researchers found that individuals with poor thyroid function were 20–113% more likely to be obese (10).
  • Developmental delays: Low levels of thyroid hormones during pregnancy, especially during the first trimester, may disrupt fetal brain development (11).
  • Bone fractures: A study found that people with poor thyroid function had a 38% higher risk of hip fractures and a 20% higher risk of non-spine fractures (12, 13).

Bottom Line: Thyroid hormones help regulate your body’s metabolism. A thyroid unable to produce as many hormones as it should may lead to various health problems.

Which Foods Contain the Most Goitrogens?

A surprising variety of foods contain goitrogens, including vegetables, fruits, starchy plants and soy-based foods.

Cruciferous Vegetables

  • Bok choy
  • Broccoli
  • Brussels sprouts
  • Cabbage
  • Cauliflower
  • Collard greens
  • Horseradish
  • Kale
  • Kohlrabi
  • Mustard greens
  • Rapeseed
  • Rutabagas
  • Spinach
  • Swedes
  • Turnips

Fruits and Starchy Plants

Soy-Based Foods

  • Tofu
  • Tempeh
  • Edamame
  • Soy milk

Bottom Line: Goitrogens are found in a wide variety of cruciferous vegetables, fruits, starchy plants and soy-based foods.

How to Minimize the Effects of Goitrogens

Man With Fork Eating Broccoli

Man With Fork Eating Broccoli

If you have an underactive thyroid, or are worried about goitrogens in your diet, there are a few simple ways to reduce the risk of negative effects:

  • Vary your diet: Eating a variety of plant foods will help limit the amount of goitrogens you consume. Plus, it’ll help you get enough vitamins and minerals.
  • Cook all veggies: Toast, steam or sauté veggies instead of eating them raw. This helps break down the myrosinase enzyme, reducing goitrogens (14, 15).
  • Blanch greens: If you like fresh spinach or kale in smoothies, try blanching the veggies and then freezing them. This will limit their impact on your thyroid.
  • Quit smoking: Smoking is an important risk factor for goiters (16).

Increase Iodine and Selenium Intake

Getting enough iodine and selenium can also help limit the effects of goitrogens. In fact, iodine deficiency is a well-known risk factor for thyroid dysfunction (17).

Two good dietary sources of iodine include seaweed, such as kelp, kombu or nori, and iodized salt. Less than 1/2 a teaspoon of iodized salt actually covers your daily iodine need.

However, consuming too much iodine can also affect your thyroid negatively. Yet this risk is less than 1%, so it should not cause too much concern (18).

Getting enough selenium can also help prevent thyroid diseases (19).

Great sources of selenium include Brazil nuts, fish, meat, sunflower seeds, tofu, baked beans, portobello mushrooms, whole grain pasta and cheese.

Bottom Line: A varied diet, cooking foods, avoiding smoking and getting your fill of iodine and selenium are simple ways to limit the effects of goitrogens.

Should You Worry About Goitrogens?

The general answer is no. Unless your thyroid function is already impaired, you don’t need to limit your intake of foods that contain goitrogens.

What’s more, when these foods are cooked and consumed in moderation, they should be safe for everyone — even those with thyroid problems (17).

Incidentally, most foods that contain goitrogens also happen to be quite nutritious.

Therefore, the small risk from goitrogens is far outweighed by other health benefits.

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