3 Reasons Broccoli May Be Dangerous To Your Thyroid

By |2019-04-22T17:48:04-07:00November 15th, 2017|Healthy Foods, Hypothyroidism|35 Comments
  • cruciferous vegetables thyroid

Did you know that broccoli is a human invention?

In fact, many of the most common cruciferous vegetables that you eat today are all human inventions.

They were all derived from the same wild mustard plant.

We’re talking about…

  • Broccoli
  • Cabbage
  • Kale
  • Cauliflower
  • Brussel Sprouts
  • Kohlrabi

All of these are the same exact species of plant that have been bred to promote different characteristics of the plant, such as larger flowers, leaves, etc.


These man-made cruciferous vegetables are much larger today and not something that we would ever have naturally consumed in such large quantities.

Yet, today large quantities of these vegetables become a staple in our modern day diet.

And it’s the “more is better” approach that can get you in trouble.

Take water and oxygen for example.

Both are essential to life.

But both can be quite toxic and even deadly if you consume too much of either.

As they say… “It’s the dose that makes the poison.”

Broccoli and other cruciferous vegetables are no different.

They contain various plant toxins designed to poison the animals that try to eat them, including you.

One such way is through their toxic effects on your thyroid and their ability to block your Thyroid Hormone Pathway.

(NOTE: If you don’t know what I mean by Thyroid Hormone Pathway then stop now and read this article here.)

This is why eating too many cruciferous vegetables can be dangerous to your thyroid health.

In fact, here’s a longer list of cruciferous vegetables that you might be eating.

  • Bok choy
  • Broccoli
  • Broccolini (Asparations)
  • Brussels sprouts
  • Cabbage
  • Canola
  • Cauliflower
  • Chinese cabbage
  • Choy sum
  • Collard greens
  • Horseradish
  • Kai-lan (Chinese broccoli)
  • Kale
  • Kohlrabi
  • Mizuna
  • Mustard greens
  • Radishes
  • Rapeseed (yu choy)
  • Rapini
  • Rutabagas (swedes)
  • Tatsoi
  • Turnips

So, before you cook up some broccoli with a side of kale for dinner tonight, let’s take a look at the three reasons why these cruciferous vegetables may be dangerous to your thyroid health.

1. Broccoli Can Inhibit Your Production of Thyroid Hormone

It’s well known that broccoli and other cruciferous vegetables can suppress thyroid function.

They do this by the plant toxins and goitrogens that are produced when you eat them.

These goitrogens and toxins include:

  • Isothiocyanates
  • Thiocyanates
  • Oxazolidines
  • Thioureas
  • Nitriles
  • Indoles

And they inhibit your production of thyroid hormone in two ways.

1. Isothiocyanates and Thiocyanates make it more difficult for your thyroid gland to absorb the iodine it needs to produce thyroid hormone.

In other words, they increase your need for iodine.

And without adequate iodine, you won’t be able to produce adequate thyroid hormone.

Because of this, they are more problematic in cases of true iodine deficiency.

And simply increasing iodine intake slightly is known to help offset the thyroid suppress effects of these goitrogens.

(Note: We do not recommend or advocate the use of iodine supplements that commonly lead to iodine toxicity and thyroid dysfunction as discussed here.)

But other goitrogens are not so easily remedied.

2. Oxazolidines and Thioureas directly block the production of thyroid hormone by your thyroid gland.

They do so by preventing iodine from being used in the process of producing thyroid hormone.

Because of this, it inhibits your ability to produce both T4 and T3 thyroid hormones.

And unfortunately in this case, no amount of iodine can help you.

These goitrogens are produced in smaller amounts compared to their counterparts.

So, eating cruciferous vegetables in small amounts infrequently is not likely to cause much harm.

But eating too many cruciferous vegetables too frequently can.

Yet, this isn’t the only way cruciferous vegetables pose a danger to your thyroid health.

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2. Broccoli Can Block Your Thyroid Gland from Releasing Thyroid Hormone

Some of these goitrogens including Oxazolidines are also known to be dangerous to your thyroid health because they can block your thyroid gland from releasing thyroid hormone.

They do this by inhibiting the proteolytic enzymes that are necessary for the release of thyroid hormone into your bloodstream.

As a result, thyroid hormone levels in your bloodstream decline…

making you even more hypothyroid.

And if that wasn’t bad enough…

3. Broccoli May Increase Your Risk of Thyroid Cancer

In well controlled animal studies, goitrogens are well known to cause thyroid cancer.

However, looking at human studies, the results are far more difficult to interpret because these studies are poorly controlled and subject to bias.

So, they are not entirely reliable and should be taken with a grain of salt.

For example, these human studies had no clear definition of what was considered a high intake of cruciferous vegetables.

In some cases high intake was considered consuming these vegetables “sometimes” per year or “sometimes” per month.

In the only study that considered high intake to be more than one serving per day found a 56% increased risk of thyroid cancer.

Doesn’t Cooking Cruciferous Vegetables Make Them Safe?

Yes, and No.

While the consumption of raw cruciferous vegetables are well known for suppressing thyroid function…

…the common belief today is that these goitrogens are easily broken down by cooking the vegetables.

However, that’s not entirely true.

Steaming broccoli until fully cooked reduces the goitrogens to about 33%, which is still substantial.

You would need to boil broccoli for 30 minutes to reduce the goitrogens by 90%!

Have you seen broccoli after being boiled for 30 minutes?

It’s not exactly appetizing.

And if you’re into fermenting your vegetables, fermenting broccoli and other cruciferous vegetables doesn’t reduce the goitrogens at all.

Don’t Cruciferous Vegetables Protect Against Cancer?

The latest news on cruciferous vegetables is that they are hypothesized to protect you against cancer.

This is one reason why people are eating more and more cruciferous vegetables today.

But remember, more is not always better.

And it may surprise you to learn that the cancer fighting chemicals derived from cruciferous vegetables are the same goitrogens that can be dangerous to your thyroid.

How, might you ask?

One of the effects these goitrogens that is being studied is their ability to act like a chemotherapy agent and kill cancer cells.

However, much like chemotherapy, healthy cells can also be killed in the process too.

And let’s not forget…

…while chemotherapy has been shown to be effective at killing cancer cells, it has also been shown to increase the recurrence of cancer too.


The cancer protective research is also rather inconclusive.

Some studies showed a decreased risk of cancer, while others showed an increased risk.

Some studies showed a decreased risk in one type of cancer along with an increased risk of another type of cancer.

Some studies showed no effects at all.

There’s a definite lack of evidence to support this claim.

And there’s a definite lack of evidence that broccoli and cruciferous vegetables should be included in your diet.

For example, many of the native cultural groups that Dr. Weston A. Price studied ate little no green vegetables, let alone cruciferous vegetables.

And their incidence of cancer was extremely low.

So what have we learned?

Everything that we’ve looked at suggests that broccoli and cruciferous vegetables should not be eaten regularly and not in large amounts.

In small amounts, adequate dietary iodine can protect your thyroid from these goitrogens.

But in larger amounts, no amount of iodine can protect your thyroid.

So, how much is too much?

Unfortunately we don’t have a good answer for that yet.

And until we do, I recommend erring on the side of caution and keeping cruciferous vegetables a minimal part of your diet.


1. Weil, Andrew. “Is Broccoli Bad for the Thyroid?” DrWeil.com, 3 Dec. 2016, www.drweil.com/diet-nutrition/food-safety/is-broccoli-bad-for-the-thyroid/.

2. Myszko, Amy. “Why Is Broccoli Bad For Thyroid?” Healthy Eating | SF Gate, 21 Nov. 2018, www.healthyeating.sfgate.com/broccoli-bad-thyroid-9761.html.

3. “The Truth About Cruciferous Vegetables and Your Thyroid.” HormonesBalance.com, Hormones & Balance, 9 Oct. 2018, www.hormonesbalance.com/articles/truth-cruciferous-thyroid-not-think/.

4. Debunking the paleo diet | Christina Warinner | TEDxOU
5. Bearers of the Cross: Crucifers in the Context of Traditional Diets and Modern Science

About the Author:

Tom Brimeyer is the founder of Forefront Health and the creator of the popular Hypothyroidism Revolution program series. Specializing in thyroid and metabolism disorders, Tom's work has impacted over 50,000 people spanning more than 60 countries. Tom is also a highly sought after practitioner who runs a successful health consulting practice where he continues to help clients across the globe to take back control of their lives from their devastating health conditions.


  1. Susan Krautter February 4, 2016 at 8:52 am - Reply

    I have been taking indole-3-carbinol for many years to assist in the metabolism of excess estrogen for excretion. From your article, I see that indoles can have a negative effect on thyroid function. Do you have a suggestion about how I can accomplish estrogen elimination without the use of indole supplements? Thank you for all your assistance. My husband Ron and I have been following your information for over a year now and have made several changes to our diet and lifestyle.

    • Tom Brimeyer February 5, 2016 at 11:50 am - Reply

      Hi Susan, I don’t recommend using I3C or DIM because they also have their own negative effects such as inhibiting metabolism and ATP production.

      And I think more focus needs to be placed on WHY estrogen is excessive and address the underlying issue. For example if estrogen levels are high because of the overconsumption of PUFAs, then simply focusing on detoxification isn’t addressing the real cause of the problem.

  2. Bob February 4, 2016 at 9:18 am - Reply

    So,,,are you sauerkraut which has great probiotics for healing the gut, the same gut that affects the adrenals and endocrine system is not a good thing? Or are you simply saying to eat in moderation said sauerkraut, and if so, what is the recommended amount per day?


    • Tom Brimeyer February 5, 2016 at 11:56 am - Reply

      Hi Bob, we’ve already established through research that the gut itself isn’t the cause of adrenal and endocrine issues. I’m not saying that they don’t contribute but they are not the underlying cause. Adrenal issues are directly related to the thyroid as mentioned in this article: https://www.forefronthealth.com/thyroid-mistakes/

  3. Anthony Llabres February 4, 2016 at 9:32 am - Reply

    For those looking to clear estrogen and are worried about DIM, they may want to look at Calcium D Glucarate, choline and inositol for helping the liver and detoxification. Would like to hear Forefront views on this and DIM.

    • Tom Brimeyer February 5, 2016 at 11:59 am - Reply

      Hi Anthony, I mentioned this elsewhere but I’ll copy it here as well. I don’t recommend using I3C or DIM because they also have their own negative effects such as inhibiting metabolism and ATP production. It also promotes oxidative stress.

  4. Dawn February 4, 2016 at 6:15 pm - Reply

    How much is the right amount? Once a week? Twice a week? Once a month?

    Roasted browned cauliflower and roasted Brussel’s sprouts are my two favorite vegetables. And we eat a couple bites of fermented cabbage every day for the probiotics. I’d hate to think I was harming myself by eating my favorite foods!

    • Tom Brimeyer February 5, 2016 at 11:45 am - Reply

      Hi Dawn, as mentioned in article we don’t know how much is the right amount or too much. The research is very inconsistent.

  5. Kay February 4, 2016 at 7:09 pm - Reply

    I’m not relying on my thyroid anymore but WP thyroid…so my thyroid is already suppressed. How does that play into eating these foods?

    • Tom Brimeyer February 5, 2016 at 12:00 pm - Reply

      Hi Kay, even if supplementing thyroid hormone this would still be a concern.

  6. Ginny February 5, 2016 at 11:07 am - Reply

    What about the popular micro greens that are so popular now? I’m also interested in DIM. My doctor has me taking 300 mg daily. My thyroid has been doing quite well

    • Tom Brimeyer February 5, 2016 at 11:53 am - Reply

      As mentioned above… I don’t recommend using I3C or DIM because they also have their own negative effects such as inhibiting metabolism and ATP production.

  7. yolanda February 5, 2016 at 4:27 pm - Reply

    Thank you for your article. I was diagnosed with Hypothyroidism about 6 months ago, I had always eaten many vegetable from the ones you listed until two years ago when I are broccoli and became very ill. It was almost as I had an allergic reaction, of course I tried eating it again because I didn’t believe that it was from the broccoli. Then it started happening with raw cabbage and cauliflower, instant bloating, stomach cramping and vomiting. I wasn’t sure of what was going on, as I never had food allergies before. A friend advised me to have my thyroid checked, my TSH levels were at 159. I still have a lot to learn and I’m still on the hunt for a doctor that will help get to the root of the problem, but Thank you again for your article.

    • Tom Brimeyer February 5, 2016 at 4:36 pm - Reply

      Hi Yolanda, thanks for sharing I’m sorry to hear about your experience. A TSH of 159 is extremely high and will result in quite a lot of inflammation. Hopefully you’re doing better now.

  8. Zainub February 8, 2016 at 6:40 pm - Reply

    Dear Tom
    ive just started your diet and enjoying it so far.
    ive been on meds for 5 years now but lately have been really not well.
    I tried the temp n pulse test and mines was not right 60.1 and 55 beats. So the thyroid hormone us definitely not getting to my cells.
    today I learnt a strange thing, my
    tsh 3.73
    Ft4 16.9
    Which means I have a high tsh and a high t4
    So im basically overmedicated and probably have a conversion problem to t3 somewhere down the line.
    I literally feel overmedicated. ..Ive decided to stop the meds come what may
    and focus on the real problem , failure to convert to T3
    Thank you so much for the great diet and the knowledge that we need to take control.

    • Tom Brimeyer February 9, 2016 at 8:03 am - Reply

      Hi Zainub, I don’t recommend stopping any sort of medication. That’s something that you need to discuss with your doctor and maybe try some more appropriate alternatives. Too much T4 can further suppress the thyroid and an inability to convert T4 into T3 is a big and very common problem among thyroid sufferers. Here’s an article that can help: https://www.forefronthealth.com/thyroid-medication/

  9. Theresia February 9, 2016 at 1:51 am - Reply

    It would be so helpful with a list of good vegetables. 🙂

  10. Zainub Muller February 11, 2016 at 11:18 am - Reply

    Dear Tom

    My blood tests came back and it doesnt look like I have a T4 to T3 conversion problem

    Tsh 2.20 uiu/ml
    FT3 4.1 PMOL/L
    FT4 20.5 pmol/L

    my dose was increased from .50 to 1 mcg

    I was literally having breathing problems and very unwell. Since stopping the medication I feel way better.

    Im not sure whats happening …I dont know if its possible that my thyroid has kicked in but my body is literally rejecting the medication

    something that interests me is that I noticed

    Alkaline phosphatase is 45 IU/L

    and im wondering whether I inactual fact have celiac/ gluten intolerance.

    I will wait for the endo on monday but so far since I find all these doctors useless and ignorant…it literally felt like I was dying when they increased my dose. I would rather take my health and the risk into my own hands.

    It will be difficult but im worse off on the meds right now and I seriously believe they just mask the real problem.

    I just cant explain how good I feel off it. Its possible that I will have side effects once they completely wear off but I guess then I will have a better idea of what exactly is going on.

    • Tom Brimeyer February 15, 2016 at 8:40 am - Reply

      Too much T4 is very suppressive of thyroid function. Many who use T4-only medications find that their symptoms worsen because of this.

  11. Jeannie April 27, 2016 at 4:46 pm - Reply

    I’m hypothryroid since birth. I have been on T4 medicine my entire life. I work full time in retail but have no energy for exercise or housework. My last tsh was just over 3 so family Dr didn’t change my dose. He did change the name brand but its still a t4 medicine. I usually eat one of these vegetables once a week. Please advise.

    • Tom Brimeyer April 28, 2016 at 1:39 pm - Reply

      Hi Jeannie, we talk a lot about the ineffectiveness of T4-only meds and how even a TSH of 3 is still considered hypothyroid. I would recommend testing your own thyroid function using a more accurate testing protocol like the one we use with our clients. We have a free training that walks you through it here: https://www.forefronthealth.com/lp/ultimate-thyroid-testing-protocol/

  12. Tania May 12, 2016 at 5:58 pm - Reply

    Tom. Please send me a copy of your recommended diet. I have Hashimotos, hypothyroidism, produce too much cortisol etc etc etc. Can’t give up wine. Exhausted most of the time.

    • Tom Brimeyer May 13, 2016 at 11:59 am - Reply

      Hi Tania, overproducing cortisol and other stress hormones is how you compensate for being hypothyroid. And here’s where you can get a copy of our programs: https://www.forefronthealth.com/programs/

  13. Jeannie J Rush May 28, 2016 at 4:12 pm - Reply

    Thank you for the reply. I had blood drawn Thursday for this year and I don’t have those results yet. My temp is always under 98 upon waking but I lose count on pulse and don’t have seconds on my alarm clock so I’ll have to wait til payday to get pulseometer

  14. Ebony August 8, 2016 at 1:55 am - Reply

    What if your the opposite, hyper?
    And you produce too much thyroid hormone. Then what? Is this recommendation the same???

    • Tom Brimeyer August 8, 2016 at 5:22 pm - Reply

      Hi Ebony, it would be important to accurately test your thyroid to validate the diagnosis. Keep in mind that low TSH and even high T4/T3 does NOT indicate hyperthyroidism. Nor does hyper symptoms, which are commonly found in hypothyroidism, due to elevated adrenaline. I would recommend using the following testing protocol: https://www.forefronthealth.com/lp/ultimate-thyroid-testing-protocol

      If this testing protocol validates hyper-thyroid, then juiced goitrogenic vegetables can be used to suppress thyroid function.

  15. Iain Russell August 13, 2016 at 1:15 pm - Reply

    Hi Tom
    Thanks for a very informative article. I added raw broccoli to my diet last year (only 300 mg per week) and within 6 months i had several symptoms common with hypothyroidism though it took me a while to join all the dots. Less than a month after quitting the broccoli all of my health issues disappeared with the exception of hair loss which has been severe, 3 months with no new growth.
    Just thought i’d share my story in order to prove how toxic raw broccoli really is.

  16. Pam Whittaker October 25, 2016 at 9:31 pm - Reply

    Great information, I hate that I can’t eat kimchi as frequently, but…I especially appreciate the mention of DIM, as I have been using that for years. I was actually losing a steady small amount of weight and it seems around the time I introduced DIM, it stopped and have been gaining weight without changing much else. I was afraid to stop using it, as I really thought it was helping with the estrogen dominance and my face broke out less while taking. I did try to stop it a few times, but I’d get breathlessness and breakouts. Have you heard of Moringa and would that be a good alternative to the DIM??

  17. Rita November 16, 2017 at 5:18 am - Reply

    What vegies do we eat? I stopped eating anything green because it makes me sick. How do I substitute for greens? What can I eat that won’t have a negative effect on my thyroid?

  18. David Clark November 16, 2017 at 5:53 am - Reply

    How about broccoli sprouts, which are revered for the sulflurophane and it’s anti-cancer, anti-everything claims?
    Do the sprouts have any appreciable goitregens, and do you think they suppress the thyroid? Sometimes the sprouting process breaks down certain components, like phytic acid, saponins, etc., wonderred if it also reduced thr goitrogens.

    • Tom Brimeyer November 16, 2017 at 5:59 am - Reply

      Hi David, the cancer claims are discussed in the article under the “Don’t Cruciferous Vegetables Protect Against Cancer?” section.

  19. Elliott Horowitz November 16, 2017 at 6:25 am - Reply

    Good Morning Tom, Could you comment on the supposed effects of cruciferous vegetables modulating estrogen. It is common practice to recommend DIM and sulforaphane to minimize conversion of testosterone to estrogen. Additionally, many of my patients minimize goitrogens in their diet but don’t see any improvement with thyroid function.

    • Tom Brimeyer November 16, 2017 at 7:13 am - Reply

      Hi Elliott, I don’t recommend using I3C or DIM because they also have their own negative effects such as inhibiting metabolism and ATP production. They also promote oxidative stress. Thyroid function involves much more than just goitrogens. It involves the entire thyroid hormone pathway: https://www.forefronthealth.com/overcome-hypothyroidism/

      We focus on addressing thyroid dysfunction from every angle.

  20. sue January 17, 2019 at 9:36 am - Reply

    Hi Tom
    I have hypo thyroid and fatty liver now is there any advice please to get rid of fatty liver and high ALT and AST ?


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