The kale-thyroid connection


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The kale-thyroid connection

“Variety and moderation.”  That’s become my food mantra since my shockingly low thyroid result in September.  I asked the question “Can you overdose on kale?”  and now, 5 months later, I am more convinced than ever that YES, you can overdose on kale.

Too much of any food – even healthy ones – can be harmful.

But I am so happy to report that after 5 months of healthy eating, de-stressing and cutting back on kale has my thyroid almost completely back to normal (woohoo!).

So what does this mean for you?  How do you know if you’re eating “too much” kale?  Should you eat it at all?  Are there other foods that can suppress your thyroid function too?  In the past 5 months I’ve done a ton of research about the kale-thyroid connection, and there’s a lot to learn.  Let’s dig in.

Why does kale suppress thyroid function?

Stick with me through 30 seconds of sciency talk, and then we’ll get back to the practical information.

Kale is a cruciferous vegetable (also known as brassicas).   Cruciferous veggies include cabbage, kale, broccoli, cauliflower, bok choi, arugula (rocket), turnips and watercress (get a longer list of cruciferous vegetables here).  There are a lot of healthy veggies in the list!

The connection with the thyroid is that in addition to their healthy compounds, cruciferous vegetables also include isothyocyanates which can inhibit the uptake of iodine by your thyroid – which decreases the amount of thyroid hormone produced and results in ‘underactive thyroid’ or hypothyroidism. (Check out this link for more techincal information on how cruciferous vegetables affect thyroid)

Rather than remembering all of this, it’s probably easier to remember that cruciferous veggies like kale contain contain goitrogens.  (From Wikipedia:Goitrogens are substances that suppress the function of the thyroid gland by interfering with iodine uptake, which can, as a result, cause an enlargement of the thyroid, i.e., a goiter.)

And it looks like goitrogens can suppress thyroid function in susceptible individuals (who are predisposed to low thyroid, or have low iodine intake, etc.)

Apparently I was susceptible!


Can I ever eat kale again?

YES!  Yes, yes yes.  Please do eat kale.  It’s tasty and packed with nutrients!

You probably just don’t want to eat it raw in smoothies, every day, for a long period of time.

Mix up your greens!  Try different greens from different families (for example, add in some romaine lettuce to your green smoothies).  And if you’re eating cruciferous veggies, try cooking them first, at least some of the time.   If you are a green smoothie drinker, here are some guidelines for rotating your greens.


What’s a ‘normal’ amount of kale to eat?

If you’re a bit of a greens addict, like me, it can be hard to remember what a ‘normal’ serving is.

This study from 1986 showed that people who ate 5 ounces (2/3 cups) of cooked Brussels Sprouts daily for 4 weeks, had no adverse impact on thyroid.   Of course, that’s cooked brussels sprouts, where the goitrogens are mostly deactivated.

I couldn’t find any research or firm guidelines on what is safe to eat for thyroid function.  So I think this is where you use common sense and listen to your body.  If you have any thyroid issues or a family history of them, really limit your intake of raw cruciferous veggies and instead, eat them cooked.

Personally at this point, I’m only eating raw cruciferous veggies as a small amount of homemade sauerkraut.  Other than that, it’s all cooked.

But that’s just me.  I’d love to hear what you’re doing if you’ve also cut back on kale and cruciferous veg – let’s discuss in the comments!


What other foods can suppress thyroid function?

It’s not just kale.  It’s all of the cruciferous veggies I mentioned above, and a few other sneaky additions:

  • Soybeans (this is one of the hardest to avoid because many processed foods include soy!  Even more reason to cook your own.)
  • Pine Nuts
  • Peanuts
  • Millet
  • Strawberries
  • Pears
  • Peaches
  • Spinach
  • Sweet Potatoes

There are also a few lesser known cruciferous vegetables:

  • maca (are you putting this in your smoothies too?)
  • canola / rapeseed
  • arugula (rocket)
  • horseradish
  • wasabi

Again, it doesn’t mean to not eat these foods – just to be aware of them if you’re dealing with a low thyroid issue.


And it’s not just foods – what about chemical exposure?

Not surprisingly, thyroid function (like most other things in our bodies) is affected by environmental toxins as well.  Even more reason to DIY your beauty products!

  • Bromine – in processed baked goods, some hard plastics, citrus flavored sodas etc.
  • Flouride – in toothpastes, urban drinking water
  • Triclosan – in antibacterial hand wash and soaps

This is an area I’m just starting to look into – stay tuned for more information on this and healthy DIY alternatives to these products!


Where can I find more information?

Over the past 5 months I’ve done a ton of research, and here are some of my favorite resources for learning more about the kale-thyroid connection (and how to nourish your thyroid back to health – naturally!)

About the author

Amanda Cook is an author, entrepreneur & alchemist. She helps entrepreneurs, business owners & executives rediscover their inner guidance, so they can create meaning, success & magic in their next stage of life & work.

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  1. This post helped me tremendously! A couple months ago I started gaining weight after cutting calories and eating 1-2 Kale salads every day. Since Kale was the main thing I changed in my diet I googled it and found your article. I realized I also had several other symptoms related to thyroid problems. I had a TSH test and it was 8.05 – hypothryoidism. Did you get your thyroid back to normal without medication? Did you take any supplements? I have stopped eating Kale (I may eat it cooked sometime after I get my thyroid back in control), but I’m wondering if I should take Iodine supplements (Kelp) to help get things regulated, did you? I would like to get things back in control without resorting to synthroid or other drugs, if possible.

  2. This article is TRUE . I had an SVT (sub ventricular tachycardia) that lasted 30 minutes from too much of a good thing (I make kale soup daily). I have Hypothyroidism and treat it naturally (and it works) however TOO MUCH of these goitrogen foods (cooked or not) is NOT GOOD. Trust me, you dont want a heart condition like I had. Great Article

  3. Hi I feel like my muscles are wasting and my limbs are as heavy as lead
    Mood is very low
    I’m hypothyroid and stopped taking mess for two weeks
    How do I convince my doctor that eltroxin is not doing me any good
    Think I need the natural hormone for my t3
    Thanks in advance

  4. Thanks for this article. I’ve been having smoothies almost daily to try to get some of this hormone-thyroid weight that seems to be increasing in a daily basis. Been using kale maca chia seeds ginger with rice milk and sprout based protein powder. Having a hashi flare up now with goite that’s returned plus my doc recently lowered my synthroid. I’m a mess

  5. How About for hyperthyroid individuals? Does it mean if they eat whats not reco for hypothyroids, their thyroid function will go the opposite direction–ie, a balanced thyroid?

  6. Juicing kale and spinach every day made me very ill. I have since removed goitrogenic vegetables from my diet and feel increasingly better. The brain fog and fatigue are much improved. There are still many vegetables to juice and eat, it is worth it to me, I feel like I’m getting my life back.

  7. Hi, I’m a 53 year old female & was diagnosed with Hashimoto’s when I was 46 and thyroid is fine. I try to eat very healthy with very little red meat/chicken, and I eat more fish and green leafy veggies. I splurge on some meats once or twice a month so I get my iron intake. My latest blood work indicated that my Thyroglobulin antibodies are 170 and my Thyroid Peroxidase is 244 which to is very high. I need help in this field any advice? I also need help in finding a good multivitamin recommendation I can take that doesn’t have broccoli,kale, cauliflower, spinach, & it needs to be gluten & dairy free, any advice which one or where to buy? I also cannot sleep very well at night, insomnia is bad to. I am desperate. I exercise everyday for 45 minutes a day for cardiovascular. I cannot afford to be fully gluten-free (to expensive) but I do buy all my veggies organic and meats to.

    1. Hi, Valerie. Do you do any type of caffeine? It can affect your adrenals/thyroid especially as you get older. As we get older, our our ovaries no longer produces estrogen and our adrenals take over and start producing it. Adrenals are stressed by caffeine and then having to produce estrogen too really stresses them out. I found cutting out caffeine as well as stevia really helped me.

  8. have you been tested for TPO antibodies??
    taking iodine can make matters worse in this case!!

  9. Hello, I did not know about the kale and thyroid connection. I have hypothyroidism, my dr has me on Rx for it, was working now it is not as well. I was drinking green juices which included the kale and other greens. No wonder I was becoming so tired. Thanks. I have some other questions about health issues, how do I talk to you about that?

  10. Hey Amanda, I too went to IIN. I highly recommend you read this book by one of the worlds leading Biochemist Nutritions Stephen Cherniske and Dr. Natalie Kather. The Metabolic Makeover “It’s All About Energy” available on Amazon.

  11. Thanks for this great info on your site. I use Kelp for Hashimotos, and stopped taking Synthroid after being on it for a decade. I have been using the kelp for 7 years now. The Synthroid stopped symptoms, but the kelp healed my body. It brought my weight back into proportion and my hair grew back within a year. Nearly 30 symptoms of underactive thyroid, all gone. I sprinkle a small amount on at least one meal every day or every other day, like salt. It’s affordable at $3 in my local asian market, which lasts a month or two. I grind it in a coffee grinder and keep it with my spices. It’s a super food that will boost the metabolism. And as an added bonus, it also increases milk flow while breastfeeding.

  12. I use kale in my green smoothies and usually have them two to three times a week. I had a thyroidectomy about 3 years ago and take Synthroid. Do you know if this will inhibit this?

  13. Hi Amanda, thanks for your article. Last year I became very strict with my diet and juiced many of the greens like Kale and felt good, then this summer I got severely constipated along with some of the other symptoms. I want to go get a blood test and thyroid test, but I hear that there are certain thyroid tests better than others. Can you recommend the best one to ask for? Thanks!

  14. i have Hypothyroid and take 75 mcg synthroid daily. Will eating peanut butter be harmful, I eat it daily. Have read this post and find it very helpful. Brenda

  15. Is there a way to test to see what foods are best for each individual. I don’t have a thyroid problem but do have other issues. I do eat lots of kale and the other vegies that you mentioned. I am gluten free vegan, so to have to cut out other things I might as well eat the containers and drink water.

  16. I eat one to two pounds of Kale a day raw and haven’t had a problem yet. It’s been about three years now.

    1. Check your tsh – if it is over 2.0 and under 1.0 you thyroid is being affected.
      marlese carroll, Nutritionist

  17. Hi…. Im really struggling with all this. I am Hypothyroid…. and am trying to eat MORE greens not less. ok so the greens I eat are Cabbage , Kale and spinich all uncooked. So if I cut these out what do I replace them with? I love my coleslaw and salads made with these, infact this is where all my greens come from. Can you suggest replacements.

  18. I found that True Leaf Stevia also affected my thyroid and made me tired. Other people have found this too. Also, gluten and caffeine can mess it up. Like you, I read and experiment with my own body to see what works.

  19. The question was asked previously but it appears to remain unanswered – can anyone say conclusively that it’s okay to have green juices with kale as long as it is steamed for some time? I’m finding it really confusing, and consequently I’ve become quite frustrated and anxious and not knowing which way to turn!

    1. Hi Gael, why not try other greens in your green juices? Variety is so important in our diets. You can try romaine lettuce, spinach, parsley, celery etc… and the occasional kale.

      1. Hi! I just found your blog and I love it, thank you. I started eating large amounts of kale and just love it…well now my tsh is super high and my thyroid is enlarged. I take iodine everyday so I didn’t think the kale would be a problem and I crave it so much! But it sounds it could be my biggest issue. What do you think about grains? Paleo diet? I know gluten/wheat is out, and do not eat it, but what do you think about grains? thanks so much again for the awesome info! 🙂

    2. I eat kale and spinach and water cress 5 days a week I am now feeling anxious about what I have read that is with my salad and other vegs

  20. Since everyone is different its hard to gauge what is good or bad really. I’ve had a thyroidectomy five years ago. BUT I had a goiter what was the size of a three year olds fist. My thyroid was so large it met on either side of my ear lobes. I was told to eat meat, eggs and very little salads and I found that astoundingly insane! I was raised vegan before venturing into vegetarianism so you can image my shock. I am now 80 pounds overweight and i struggle to not gain anymore weight. I don’t eat a lot of food really as i want. My Internist took me from 100mcgs to 150mcgs of Synthroid and i hate it greatly. I am kosher so armor is not even a thought to use. I’ve read until I am blue in the face of this or that or no this is better that i grow weary of it all. A question? Is there one for people like me to ask? I have no idea fighting this battle alone daily and some times hourly. I would like to just get back to me but the saying goes “one can never go back and now I believe it”

    1. Aprille…have you tried adding a synthetic T3 to your Synthroid? You most likely are not converting Synthroid’s synthetic T4 to T3, and your body cannot live on T4 alone. I have had dramatically excellent results after switching to Armour, even though I too am vegetarian. But, I am not kosher, so I consider getting my life back priority over my vegetarianism. Anyway, this is why I recommend synthetic T3 for you. Good luck, it’s so terrible to feel like your life is over, isn’t it….

    2. Hi Aprille, I believe the laws of eating Kosher or Halal against pork are only waived for medication that is needed to save your life. So I take Nature Throid and it works far better than ANY synthetic thyroid medicine I have tried. I have been struggling with this issue since 2009 and last year I finally came to the realization that God would prefer me to live better than suffer with Syntroid and all of its side effects and the damage it was doing to me. I did try Amour but it was not consistent. Nature Throid has really helped.

      1. Do you drink coffee or caffeinated drinks? If so, google “Womens Health Network “. They are an incredible resource. For hair loss and fatigue, they tell women to quit caffeine and gluten. For me, it worked, They used to be called, “Women to Women”. Anyway, they give out lots of info and have been helping women with these issues for 25 years!

    3. I was on Synthroid for over 11 years until I went to a naturalpath doctor who switched me to Armour Thyroid. I can’t believe the difference. I actually feel normal. I should have switched years ago. Plus, my levels are no longer bordering on the high side anymore.

  21. My 12 year old daughter was diagnosed with hypothyroidism 3 years ago. She is currenlty taking synthroid. Is this safe? I’m not comfortable about her taking medicine so early in her life but the doctor recommended it. How can I help my daughter? Any advice would be so greatly appreciated.

    1. I recommend Armour Thyroid. This is a natural treatment for Hypothyroid from pig thyroid. This is what was used before the synthetic Synthroid was created. You will be told that it is less consistent but that is fine for me. I want natural not chemical support. Many who have used both will tell you that Armour was better.

    2. It depends, if she has Hashimoto’s or just a thyroid problem. Hashimoto’s is an autoimmune disease that comes and goes, she may be able to come off her meds but you need to figure out her triggers. For me, my antibodys go up with soy, stress, and a lot of the foods mentioned above. Supplementing with 200mcg of selenium really helps. At 12 it’s most likely Hashimoto’s. Find out, there are great books on it and you can teach her how to care for herself and preserve her thyroid. Thyroid effect progesterone levels, it will effect her periods and total health. Try reading, What Women should know about Hormones, by Dr Pamela Smith. Good luck!

  22. Thank you so much for this article. I just got my blood test back and indicated that I had hypothyroid at 8.4. I have never had a thyroid issue. The doctor thinks that this happened in recent months anywhere from 2-6 months. I questioned my diet because I am very healthy. I researched Kale and Low Thyroid which really helped me understand why. I’ve been juicing everyday and with Kale everytime. Not only that, I was eating Kale in salads as well. It really was overdosing on Kale. Although my doctor referred me to a endocrinologist, I am going to hold off on it. I am going to eliminate the kale in my diet, take another blood test and see if it lowers. I really believe this was the culprit of my problem.

  23. I just read your post, and then read the link to Mercola’s article about thyroid that you provided. He advocates eating foods that in other articles are said to suppress thyroid function. This is what is confusing to me — one article says do this, another says DON’T do that, do this instead. Anyway, Mercola says to eat lots of spinach, kale, sweet potato. I am confused.

  24. HI

    I’ve been Hypothyroid for over 20 years. This past January, my thyroid went nuts. I ended up losing 70 pounds in 4 months – something most Hypothyroid patients don’t experience. I changed doctors since my thyroid levels were bouncing all over the place. I choose an Osteopath and also went to a holistic Chiropractor who also does nutrition – he saved me. After running alot of blood test, my nutrition was lacking greatly. He removed alot of food groups, but included sweet potatoes and spinach. My Hashimotos test came back negative, however, from my research, it’s more of a “flare” up auto immune disease and the test was done when I felt alot better. I’m also on many supplements, including high vitamin D and iodine. After months of chaos and extreme weight loss, I’m finally feeling so much better. However, I still have to “create” most of my own energy. I always feel so much better after I workout. I take Zumba and Yoga classes – and many times I have to force myself to go. I’d rather fall asleep but I know this exercise will give me the energy that I’m lacking. I still have a thyroid that wants to overproduce at random – but overall my holistic chiropractor has given me my life back…..

  25. Hi Amanda, I found this site because I was looking for Kale Effects. Reason I search for this is because for the past 2 nights, I had hard time falling to sleep, it took a long time to fall to sleep and in the morning, I feel so tired and hard to get up bed. I started to think back what I ate or do that can cause this, then I realized, for the 1st time, I ate the dark green kale as shown on top of this website, I ate it raw for lunch, then cook it and ate for dinner on 1st night and ate some for dinner on second night but also ate lighter kale raw for lunch on 2nd day. I wonder this cause the sleep problem and tiredness in the morning. Is there possible connection there? Thanks.

    1. Hi, I’m not sure about the sleep problems or fatigue. An easy test is to stop eating the kale and see if it improves?

    2. Hypothyroidism can cause sleep apnea. If left untreated, it can lead to heart failure, diabetes, anxiety attacks, and a bunch of other conditions that you don’t want to get. You should ask your doctor for a sleep test with MSLT. If it’s negative, you can at least rule it out. I ended up with sleep apnea post- thyroidectomy. I still think that my docs are keeping me too hypo even though all of my thyroid levels are “within range”. Not everyone’s body reacts the same to any drug.

  26. I just found out about this myself, that foods can effect my thyroid. My blood tests are always coming back strange too high, too low, almost perfect then back too low again. And lately I’ve been falling asleep at work and have felt just drained everyday, not to mention the shakes I get (that’s normal when my thyroid is off). I thought it was my meds then I found out about soy and gluten-which is basically my whole diet right there.. I have cut WAY back and I’m starting to feel better.
    I came across this site because I just bought some kale chips and was wondering if they would effect me… I seem to have a sensitive thyroid and I’m glad I came across this.. thank you so much. I won’t be eating them. I can almost bet it will effect me.
    I’ve found that thyroid problems are not fixed with meds alone. And around where I live doctors don’t tell you these things, do be very aware of what your body is telling you.

  27. Hi! I have had hypothyroidism since I was 16 (now im almost 26) no doctors ever told me about avoiding foods and I only found this out recently. Last week after an ultrasound, they found a nodule that is just under the size to biopsy. I see you’ve said your levels have gotten better? Is that from medication as well? Im on synthroid and not a big fan of it. Any diet tips you have would be very much appreciated! Thanks for this post!

  28. What kind of doctor or specialist is best to work out a hypothyroid? I’m currently on synthroid and I want to ween myself off. I also want my hormones to be balanced, etc. without using synthetic drugs. Nutritionist? Endocrinologists?

    1. Hi Jennifer, I’ve had good luck working with a naturopath. In some US states naturopaths are qualified as primary care physicians too.

    2. A few years ago I was diagnosed Hypothyroid. I was resistant to taking a prescription after reading about the drugs. A friend told me about a Chiropractor with a PHD in nutrition . He suggested Thytrophin PMG and GTA Forte . It works great and no side effects :).

  29. any comments on wheat grass in smoothies..i just bought dried powered wheat grass….

  30. I have been juicing 2 bunches of kale in a juicer daily (yields about 1/2 cup of juice or a little less) for the past 10 years. No thyroid problems yet 🙂 I haven’t been taking iodine, and the salt I use does not have iodine in it (sea salt). I get about 35% of my daily RDA of iodine from a multivitamin that I take but that’s about it. I never eat kelp. Maybe I am getting my iodine from somewhere else? Dunno, but it has worked for me so far.

  31. The harmful compounds are destroyed when cooked, right? I don’t see that clarified here. I find that cruciferous veggies are much tastier and easy to digest cooked anyways.

  32. What about when you have a hyperthyroide problem ? Does kale helps keep the thyroid fonction to slow down ?

  33. This is a great article. I have Hashimoto; I guess at this point I need to figure out what I CAN eat. :/

  34. I am so happy to have found this information. I know I still need to do a bit more research but right now I feel pretty convinced that my enormous kale consumption has been making me ill. Over the past few months (and now excessively in the last few weeks) I’ve noticed that I’ve been increasingly more tired overall, almost every day. It’s not a kind of achy fatigue or muscle fatigue, but more of a sleepiness that rarely leaves me. I have always been able to operate well and with high energy on five to six hours of sleep per night, but lately I’ve been wanting to nap in the afternoons, and sometimes I’m sleepy by 7:00 or 8:00 pm!

    I am almost entirely vegan, so naturally I started to search for answers to my increasing tiredness in my diet – what was I missing? I felt certain, in my body, that I was lacking something or else getting too much of something. I’ve noticed that I’ve had these periods of time where no matter what I eat, I feel unsatisfied. No food that I consider eating seems appealing, and so I just settle on something healthy – but then I feel full and also still hungry at the same time. The overall feeling is one of my body being dissatisfied, or a feeling like I’m just not processing or absorbing what I’ve eaten.

    I started to get really scared in the last few weeks because I cannot keep my eyes open past 9:00 pm most nights, and I’ve been wanting to just lay down in the middle of the day like I mentioned. I was trying to read a book out loud last night to my partner and I was so sleepy I started slurring my words and almost falling asleep sitting up. Right then I had a brief dream/vision that something was actually really wrong, and that I needed to address it, and all of a sudden I felt a clarity that it had something to do with the kale in my diet. I’ve been researching it for a few days, as I had a suspicion it might be that, but only after last night did I feel really strongly that it was related to kale and I just found your information today. So again, thank you.

    And just so you know what my kale intake has been, for about the last six months I’ve had a pretty regular intake of RAW kale salad (sometimes with other mixed greens but the bulk of it kale) – nearly every day I ea one to two salads. I occasionally skip days, but I would say on average I eat 9-11 raw kale salads per week. I am going to go off it now and see how I feel. How long do you suspect it would take for my thyroid to get back to normal?

    1. Hi – have you gone to the doctor to get blood tests? Probably a good idea if you’re experiencing strange symptoms.
      Personally I felt better within a couple of weeks but it took a couple of months for my blood work to get back to normal. It will be different for everyone though. I would talk to your doctor about it and get some tests done, so you know for sure what’s going on.

  35. is one cup of Kale every day as bad? I use that in my Green smoothie too, but only one cup… should I switch to swiss chard once in a while?

    1. Hi Lou-Anne, in general it’s good to have a variety of foods in your diet: and especially with raw greens! So change it up a couple of times a week – try adding spinach, or romaine lettuce, or even a little bit of parsley or coriander/cilantro to your smoothie instead of kale some days.

      1. What I read said cruciferous vegetables also included SPINACH, kale, chards, broccoli, cauliflower, mustard greens, etc. had the goitrogens.

    1. I was eating it raw most days (in green smoothies) or just very barely cooked as a side-dish. Nothing wrong with eating kale … it just needs to be varied with other greens (everything in moderation!), which I didn’t do! Lesson learned!

  36. Very interesting article! I have Hashimoto’s thyroid disease (the autoimmune version of hypothyroid) and have been trying to carve out time to research ways to improve my thyroid function with food. I will be referring back to the links, but in the mean time I’m happy that I enjoy my cruciferous veggies much more cooked 🙂 Unfortunately some of the other foods you listed are big staples in my house – need to do more thinking on how to find the right balance!

  37. Great article! I knew about the Kale and Soy connection awhile ago but didn’t know about the Maca connection! Thank you!

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