Thyroid School, Issue #16// Cruciferous Veggies

Ah, the debate over broccoli (and other goitrogenic foods) and thyroid health dates back to the 1950’s when research came out about the negative effects of foods like cruciferous vegetables like broccoli, kale, cabbage and other “goitrogenic” foods on thyroid status.

Early literature from the 1920’s-1950’s on goitrogenic foods shows these compounds naturally present can interfere with the uptake of iodine (one of the building blocks of thyroid hormone) and reduce thyroid hormone production, leading to hypothyroidism. This has led to the universal suggestion to avoid goitrogenic foods if you have thyroid dysfunction.

However, newer research shows there is more to the story than face value and that certain goitrogenic foods can actually be protective of thyroid health.

The fine print that isn’t discussed from this earlier research: that the intake of goitrogenic food was problematic in the presence of iodine deficiency. Beyond that, even newer research available shows that inclusion of cruciferous vegetables is beneficial with or without iodine deficiency—especially for those with Hashimoto’s.

The finer print: the amounts that need to be regularly consumed are pretty high… much higher than would be likely unless you’re juicing or are a raw-vegan.

Let’s dive deep into goitrogens, what they are, why they matter, and how to safely incorporate them. Per usual, this is just general information and not specific advice, so definitely discuss with your provider about the best course of action for you!

Goitrogens can affect the thyroid in three main ways: 

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.

Types of goitrogens:

Compounds that are classified as “goitrogens” include those that metabolize into thiocyanates, glucosinolates, flavonoids and goitrin. Iodine at high doses can even be considered “goitrogenic”, especially when combined with selenium and glutathione deficiency. Nutrient deficiencies including selenium, iron, and Vitamin A have a goitrogenic effect. And, lastly, smoking, PCB, nitrates, perchlorate, disulfides, and lithium extend a goitrogenic effect.

Cruciferous vegetables are often the most controversial topic because they’re  so nutrient dense, but have also been given a reputation for being “anti-thyroid”. Cruciferous vegetables (broccoli, cauliflower, kale, Brussels sprouts, cabbage) contain a group of sulfur-containing compounds called glucosinolates, some of which are known goitrogens. 

Mechanism of action

When these raw cruciferous foods are chewed up and/or chopped, an enzyme called myrosinase is released and breaks the glucosinolates into smaller particles: isothiocyanate and thiocyanates. These goitrogenic molecules are potent rich antioxidants that are anti-cancer, but can block the TPO (thyroperoxidase) enzyme that helps with the creation of thyroid hormones. (Read more about TPO here).

There are human and animal studies released over the past several years that put the fear of eating cruciferous vegetables to rest. In fact, these studies even showed positive effects on thyroid status, including decreased TSH, increased T3 and T4 hormone. Inclusion of cruciferous vegetables even decreased oxidative stress (which is good!).

The production of thyroid hormones within the thyrocyte (cells of the thyroid) naturally produces a tiny bit of hydrogen peroxide that is, of course, inflammatory to the thyroid. Ideally, there is enough selenium and glutathione (important antioxidants) available to “quench” (AKA calm down) that inflammation. In the case of Hashimoto’s, which is an inflammatory autoimmune disease, antioxidants are in higher demand as a means to control inflammation. Many of these important antioxidants can be provided via the inclusion of crucifers in the diet.

Producing thyroid hormone requires adequate iodine. While this problem has become less with the iodization of salt in developed countries, the increase in iodine with subsequent decrease in vegetables in the Standard American Diet has led to too much inflammatory byproduct (hydrogen peroxide) with not enough antioxidant to quench it. Iodine is important and necessary, but getting it balanced with antioxidants is the takeaway. Additionally, too much iodine intake can itself be goitrogenic, so it certainly is a Goldilocks nutrient.

How to incorporate crucifers safely

Preparation and proper digestion of cruciferous vegetables makes all the difference. Plants naturally contain compounds that repel pests and act as defense against bacteria, fungi, insects, herbivores, and humans. These compounds can be decreased through the cooking process, proper chewing, fermentation, and interaction with the vegetable fibers and intestinal bacteria.

  • Cooking: one study gave volunteers 150 grams of cooked Brussels sprouts (which is about 1 3/4 cups) daily for 4 weeks and saw no negative changes in thyroid status when assessing TSH, T4, and T3.
  • Properly chewing your food. When you’re chomping your veggies, you’re breaking up plant cells. The cells that contain glucoraphanin and the cells that contain myrosinase are separate until the plant is damaged through the mechanical means of chewing. After they’re damaged, they can combine and create sulforaphane— a potent, anti-cancer, anti-inflammatory antioxidant.
  • Balancing your gut bacteria. Studies show that the presence of beneficial bacteria play a role in the breakdown of cruciferous vegetables and determines how much beneficial antioxidant is produced through the digestive process and bacterial fermentation.
  • Getting adequate variety. There’s nothing flashy about this recommendation, but we all need to hear it sometimes. If you find yourself eating broccoli as your main vegetable and are doing so multiple times per day for several days in a row, you may want to consider getting more variety. Try alternating with non-cruciferous vegetables like asparagus, spinach, bell peppers, green beans, and others.
  • Avoid any extremes. This also goes without saying, but I can’t help but mention it. If you’re juicing, doing a smoothie fast, or eating copious amounts of raw cruciferous vegetables, that’s probably not a good idea for anyone… especially with thyroid issues.
  • Consider fermented foods. Okay, if you’ve followed me long enough, you KNOW my love of sauerkraut. So much so that my husband makes about a gallon a month! Fermentation of cruciferous vegetables like in kimchi and sauerkraut has been shown to decrease “harmful” goitrogenic compounds and increase beneficial antioxidant, vitamin, and probiotic content.

What else can you do?

  • Check micronutrient status. Micronutrients are definitely a Goldilocks situation too. Eating a ton of cruciferous vegetables without adequate iodine may be problematic, but getting too much iodine without enough cruciferous vegetables (notably the selenium and glutathione you’re getting from them) is potentially more problematic.
  • Consider working with a professional to evaluate your diet. This is way more advanced than tracking macros in My Fitness Pal. It takes a person who understands biochemistry, food science, and your unique situation to determine the right course of action.
  • Balance your gut flora. Step one is inclusion and diversity of your fiber intake, which is the best predictor of gut health, as fiber determines how well your gastrointestinal tract produces bacteria. Next, add in probiotic-rich foods like sauerkraut, kefir, yogurt, kimchi, etc. (If you specifically do not tolerate dairy, then you can ignore that idea). Lastly, consider comprehensive stool testing to determine your unique gut bacteria balance and what you can do to fix it ( probiotics, supplements, etc.).
  • Don’t miss the forest for the trees. It’s easy to hyper-fixate on the headline and not read the entire article, including the fine print. Blindly following advice without any room for nuance or taking into account your personal situation can be detrimental.

Until next time,


Disclaimer: Please note that “Thyroid School” emails from Chews Food Wisely, LLC (and Nicole Fennell, RD) are not intended to create any physician-patient relationship or supplant any in-person medical consultation or examination. Always seek the advice of a trained health professional about any questions you may have regarding a medical condition and before seeking any treatment. Proper medical attention should always be sought for specific ailments. Never disregard professional medical advice or delay in seeking medical treatment due to information obtained in “Thyroid School” emails. Any information received from these emails is not intended to diagnose, treat, or cure. These emails, websites, and social media accounts are for information purposes only. The information in these emails, websites, and social media accounts is not intended to replace proper medical care.

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