Thyroid Doc: Kale Risks ‘Theoretical’ But In Reality, Very Low To Minuscule



This post — “The Dark Side of Kale (And How To Eat Around It)” — went wildly viral this week, generating huge traffic and high passions over this once minor but now hotter-than-hot vegetable. Among the accusations from readers were charges that the post was “dubious and dangerous” and that I was, in effect “discouraging Americans from eating vegetables” (my children would disagree).

Still, for a medical reality check, I turned to a doctor who specializes in treating the thyroid.

(Before we get to him, for background, my post was inspired by an earlier piece in The New York Times on potential thyroid problems linked to kale and other cruciferous vegetables, called “Kale? Juicing. Trouble Ahead.” This article was troubling to me since I, too, am a devoted kale fan.)

OK, back to the thyroid expert, who points out that this debate is particularly timely since January is Thyroid Awareness Month.

Dr. Jeffrey Garber is chief of endocrinology at Harvard Vanguard Medical Associates, and lead author of the latest clinical practice guideline on hypothyroidism in adults. He agreed to answer a few more questions on the kale-thyroid connection.

I’d sum up Dr. Garber’s take on the whole kale issue pretty simply: It’s probably unwise to embrace a long-term, pound-a-day raw kale habit, but even if you do, you will, in all likelihood, be fine. (Especially if you live in the U.S., where iodine deficiency isn’t a huge problem, and if you don’t have a family history or predisposition to thyroid disorders.)

“If one isn’t a food faddist or predisposed to a thyroid problem (family history, prior diagnosis) the risks are very low,” Garber said. And, he adds, if you have any concerns at all, check in with your doctor for a simple thyroid test.

Here, lightly edited, is our Q&A:

RZ: In plain terms, what’s the connection between kale, a cruciferous vegetable, and thyroid function?

JG: There are many substances that can interfere with the way the thyroid functions. Goitrogens, as in those that promote goiter, make up one of these categories.
(There’s an enormous amount of interest in environmental goitrogens, like BPA and other substances, but that’s another story: We’re talking about dietary goitrogens here.)

When you get into the way goitrogens can affect the thyroid directly there are three general ways (and all relate to iodine, which is what thyroid hormone is made from):

1. the way the thyroid picks up the iodine;

2. the way the thyroid produces the hormone once the iodine is in the thyroid;

3. the way thyroid hormone is secreted into the bloodstream.

When you look at dietary goitrogens, they interfere with one or more of these three steps.

OK, so kale is one of these so-called “goitrogenic” foods, right?

Yes. And [quoting from a section in the textbook The Thyroid, written by Michael B. Zimmerman, MSc, MD, Professor of Health Sciences and Technology at ETH Zurich in Switzerland] other cruciferous vegetable implicated as goitrogens include: cabbage, cauliflower, broccoli, turnips, rapeseeds — they contain something called, glucosinolates, their metabolites compete with iodine for thyroidal update. Similarly, cassava, lima beans, linseed, sorghum and sweet potato contain cyanogenic glucosides; these may be metabilized to thiocyanates that compete with iodine for thyroidal update. Also, if you don’t have enough iodine, deficiencies in selenium, iron and vitamin A can make you even more vulnerable to developing an underactive thyroid.

[An aside]: Iodine deficiency isn’t generally a problem in this country. It’s hard to avoid iodine in the diet here: many breads, dairy and salt (except for “designer” salts, kosher salt and sea salt) contain iodine. But in poor, developing countries about one billion people have an iodine deficiency that can cause an underactive thyroid and endemic goiter.

So, what’s the bottom line here? Green smoothies everyday or not?

Basically the goitrogens are challenges to the thyroid. But in the absence of iodine deficiency, substantial or prolonged ingestion of dietary goitrogens and lastly the absence of an underlying thyroid disorder, the risk in this country of having problems in this area are very, very low, almost minuscule. Again, that’s because the vast majority of people have adequate iodine levels to counteract the effect of goitrogens.

So, the writer of The New York Times opinion piece, Jennifer Berman, said she stopped consuming kale juice daily after she was diagnosed with hypothyroidism; when she looked up foods to avoid, kale was at the top of the list.

She gave herself too much credit for what happened to her.

But if you actually drank a green smoothie with raw kale everyday for a long period of time and somehow managed to be iodine deficient, could you do this to yourself?

It could theoretically happen, but it would be unusual.

I’m still kind of confused by all of the information out there. If I Google “Hypothyroidism And Foods To Avoid” several sites have some variation on the advice Berman got: steer clear of kale.

I think it’s overplayed.

And what about children? It’s hard enough to get them to eat veggies at all.

My strong personal opinion is to follow standard, conventional nutritional advice for kids.

We should end here by stating the obvious: vegetables are, in general, fabulous for your health; and any kind of obsessive, extreme diet that includes massive consumption of a single food can, in general, lead to trouble.

Readers, thoughts?

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  • TheBride

    Not me. I started eating kale several weeks ago and became quite ill. I had NO IDEA why until I realized that I had become very deficient in iodine. I was besides myself trying to figure out what went wrong. I probably was mildly deficient to begin with–but kale put me right over the line. Be careful! Eat kale in moderation!

  • Jeanne

    25 years ago I was diagnosed with hypothyroidism and put on medication. I have been on medication since then. Just recently I have included Kale in my diet in the form of green smoothies. I do perhaps 2 cups of kale a day. I am wondering if someone can tell me if this is or will cause problems with the thyroid.

  • Cockhran Polecat

    Kale all hail to kale it numbs the vibrant midnight striker n toker.

  • Brittany

    Okay so people who have already been diagnosed with Hypothyroidism / Hashimoto’s like myself I have been on synthroid for the past 11 years since I was 13, currently my dosage is 175 mcg. Is okay to include Kale or any of the other foods mentioned in the article, in my diet? Or should I keep it at a minimal?

  • Mary Shomon

    Neither thyroid disease diagnosis/treatment — nor the advice about goitrogens like kale — should be viewed from a one-size-fits-all, black and white perspective.

    Much of the goitrogenic effect of foods like kale is eliminated by steaming or cooking. So anyone who claims categorically that “all thyroid patients should avoid eating kale” is not offering valid, scientifically-based advice. When properly prepared, most goitrogenic foods can be safely incorporated in moderation into a healthy diet for any thyroid patient. (Soy, which when overconsumed can also inferfere with the body’s ability to absorb thyroid hormone, is an exception.)

    At the same time, there is no question that overexposure to raw goitrogens — particularly for those who may be iodine deficient — can trigger thyroid irregularities in some people.

    I agree with Dr. Garber in that a “long-term, pound-a-day raw kale habit” could be problematic. I’d add a caution regarding daily raw juicing of goitrogenic vegetables.

    Where I disagree with Dr. Garber is in saying “Iodine deficiency isn’t generally a problem in this country.” In reality, the National Health and Nutrition Examination Survey (NHANES) III –1988-1994 — saw drops in U.S. iodine levels (1), including several population groups — pregnant women in particular — who had insufficient levels (2).

    We don’t need to avoid nutrition-packed cruciferous vegetables out of a fear of thyroid disease. We should, however, make sure that the public is cautioned about the potential for iodine deficiency, to avoid overconsuming raw goitrogens, and thyroid patients whose thyroid function is not optimized and balanced should evaluate the potential dietary impact of goitrogens on their thyroid function or treatment effectiveness.

    Mary Shomon
    Thyroid Patient Advocate/Author



  • Celia Harrison

    Just throw some powdered Kelp in your smoothy or vegetable juice and counteract the decrease in Iodine.

  • Alastair Haigh

    It’s spelt “minuscule”.

  • Nancy

    I do have low thyroid and I can claim eating these raw vegetables do effect me. I find it best to cook them. I take both T-4 and T-3 and if I am not careful my fingers or my lips swell for 12-24 hours and it is very uncomfortable. I’m finding it difficult to play the game of taking the meds and when to get these not so good for me vegetables, and nuts timed so the meds & veggies work in the right order. Anyone with low thyroid needs to learn all about it, most general doctors have no clue about how the thyroid really works or how to read thyroid blood work.

  • Allison Dee

    Um… the NYT piece that sparked all of the panic was a HUMOR piece about people taking health fads too seriously. How did this escape anyone who actually read it?!?

    • vito33

      How did it escape them? I’d invite you to check out a satirical website called “The Daily Currant”

      Read a couple of the obviously fabricated stories and then scroll down to the comments section and take note of all the people who believe they’re reading actual news. (It’s pretty scary to think that a lot of those people vote.)

    • Expatmom

      Yes, humor sparked a real life discussion. That’s a good thang!!!!

  • Matt McCandless

    What out for kale! Oh… Wait… Never mind…At least there aren’t many commercials.

  • Shelley Chancey

    The biggest message seems to be lost on most Americans– Moderation!!

    As a Graduate Student/Dietetic Intern, I’m concerned when *anyone* starts recommending cutting out an entire food group from a daily diet (especially without knowing an individual’s medical history).There are several things that I heard from every professor in every class I had: be concerned anytime a food group is said to be cut out (*without* medical necessity) and that every meal plan/diet is customized to fit the individual’s medical conditions, preferences, and availability. The biggest one of all: Moderation is *key*!!

    I’m going to make an assumption (gasp!) that this Dr. Fleckenstein, author, also has a book that advocates cutting out an entire food group for some reason.
    With the research I’ve completed (thank you for having access to a wide variety of databases in the school library!), I have *yet* to see this research indicating that milk is detrimental to us Americans.
    Considering the fact that “we” don’t get enough calcium, osteoporosis is a very real concern (especially for females), and most Americans cannot name a high-calcium vegetable, I find it highly irresponsible that someone would advocate cutting out milk. Of course, the gluten fad is another story entirely… that’s for another discussion!

    Unfortunately, the messages of moderation and well-balanced meals and diet have been lost in all the “talk” from someone (be it celebrity or otherwise) trying to sell a book, agenda, etc. How sad that the “public” will believe that cutting out complete food groups will allow us to be “healthy” without realizing that there are many consequences to these actions and other “fad” measures.
    (Think about it– do other cultures cut out complete food groups from their diets? No, they eat a lot less animal proteins–more plant proteins in their everyday meals, they have whole grains at every meal, eat a *wide* variety of plants at *every* meal, drink moderate amounts of alcohol, AND they exercise everyday!!
    I experienced this first hand with an Alumni trip to Greece and Turkey as well as one of my classmates in Undergrad was from Cyprus.)

    • Expatmom

      Are there any foods that reverse hypothyroidism???

      • alexafleckensteinmd

        Seaweeds are often recommended. In my practice I have seen many patients who tried seaweeds, but I have not really seen a case of total reversal of a sluggish thyroid.

        The reason might be that hypothyroidism might be seen as sort of burn-out syndrome. After many years of inflammation (from foods and environmental toxins), the thyroid gland just might not be repairable.

        So, try some seaweeds, but if they don’t work, move on to thyroid substitution. I am sold to the idea of natural solutions, but after the removal of half of my thyroid, I am relying now on a commercial drug. For many years already.

        And to answer your possible next question: I have not found the “natural” forms of thyroid substitute pills satisfying: They come with too many interactions and cautions to be useful in the real world. But see for yourself!

        Alexa Fleckenstein M.D., physician, author.

        • Expatmom

          Thanks for the info, Doc. Guess I’ll be sticking with the Synthroid.

        • Satya

          Wow seriously? I’ve worked in Thyroid healthcare for nearly 2 decades, anyone who works with thyroid should know not to tell someone to take seaweed, iodine, etc without making sure they are tested for thyroid antibodies. There is plenty of research on this showing these can cause extreme fluctuations and side effects including swelling of the thyroid and breathing difficulties mimicking sleep apnea from it in those with Hashimotos.

      • Shelley Chancey

        Unfortunately, there is no MNT (Medical Nutrition Therapy) for hypothyroidism… it is mostly a “medical” issue and technically falls under the realm of Endocrinology.
        From Krause’s Food & Nutrition Therapy 12th Edition 2008: Seafood (clams, lobsters, oysters, sardines, other saltwater fish) are your best sources of iodine (approximately 300-3000 mcg/kg). Fresh water fish contain 20-40 mcg/kg. Animal milk, eggs, and vegetable iodine content are based on what is consumed by the animal and the content of the soil.
        Iodized table is the form in which the majority of Americans consume (sea salt has 1/10 the iodine content of table salt). Hypo- and Hyperthyroidism is not as common of a problem as Goiter is in the rest of the world. This is why many countries require their salt to be iodized (the US does not have this mandate as goiter is very rare here).
        Bread, 1 slice, made with iodate dough conditioner and continuous mix process = 142 mcg
        Haddock, 3 oz = 104-145 mcg
        Bread, 1 slice, made with regular process = 35 mcg
        Cottage cheese, 2% fat, 1/2 cup = 266-71 mcg
        Shrimp, 3 oz = 21-37 mcg
        Eggs, 1 = 18-26 mcg
        Cheddar cheese, 1 oz = 5-23 mcg
        Ground beef, 3 oz = 8 mcg
        Daily Recommended Intakes (DRI) and Recommended Daily Allowances (RDA) for Adults is 150 mcg/day.
        *mcg = micrograms

        • Expatmom

          Great info, thanks so much. I live in south La & consume lots & lots of seafood. So do my friends. The menopausal ones are all on thyroid medication. The men aren’t. What gives?

          • Shelley Chancey

            Not only is seafood helping us with the iodine, its great for heart & brain health in the form of Omega 3 & 6 fatty acids (healthy fats!)
            Unfortunately, the ladies get the short-end of the stick on many things (compared to males). As for why? Academia is still trying to figure that out. Of course, genetics plays a large part, but there are so many other factors at play, too (environment, etc). Your primary care physician/OB-GYN might be able to lend some insight into all of this, knowing your personal history.

      • Dawn Stancel

        if you are overweight- lose it. my friend just lost 70 pounds and had been on thyroid meds for years. she is now completely free from all prescription meds. Her thyroid levels are normal now. This is not the answer for all people but it is amazing if we would be a healthy weight then many health problems would not exist.

        • betzib

          The problem is that it’s nearly impossible to lose weight when you have hopthyroidism.

          • Dawn Stancel

            She had hypothyroidism and lost 70 plus pounds. she had to come up with her own method- the doctors weren’t working. she figured out what her stressors were that caused weight gain and eliminated them. if they were people that caused stress then she would make sure that she cut down her time with them some way. She eats around 50 NET carbs a day, she completely cut out grains and sweets, only one day a week she will eat a low calorie sweet and have grains so that she wouldn’t binge and fail. she also exercises and keeps a food diary. she has done it herself and it works without outside help. She is still on her journey to her goal weight. When she reaches a small weight goal, she’ll reward herself someway (mountain bike is an example)

          • TheBride

            Right you are. I’m not really overweight but gained about 15 pounds (that I hate) after I developed thyroid cysts. Take kelp, it will increase your energy, your mental acuity, and decrease fluid retention–naturally. So, do it–it will not hurt you!

      • Dawn Stancel

        my friend had hypothyroidism and lost 70 plus pounds- she is cured from it. she had to come up with her own method- the doctors weren’t working. she figured out what her stressors were that caused weight gain and eliminated them. if they were people that caused stress then she would make sure that she cut down her time with them some way. She eats around 50 NET carbs a day, she completely cut out grains and sweets, only one day a week she will eat a low calorie sweet and have grains so that she wouldn’t binge and fail. she also exercises and keeps a food diary. she has done it herself and it works without outside help. She is still on her journey to her goal weight. When she reaches a small weight goal, she’ll reward herself someway (mountain bike is an example).

        • Expatmom

          I don’t have a weight problem. My BMI is 22.8.

        • daughterofsnape

          I didn’t do anything to resolve my hypo-thyroid, but it just sort of corrected itself after being on cytomel for several years. My doctor took me off of the cytomel and tested my thyroid and said it was normal now. I have my doctor test it yearly and he says it is still normal. When they put me on the medicine, my numbers were off by a huge degree. I don’t remember the numbers, but one that was twice what it should be, and the thyroid hormone was super low.

          Anyway, I think that sometimes it does seem to get back to normal after being on treatment for a while.

      • TheBride

        Take kelp. It will help relatively quickly. And it will help you lose weight because your energy will be increased. It will also help with water retention (that is common with low thyroid function).

    • Celia Harrison

      Typical hospital dietician.

      • Shelley Chancey

        btw– it’s Dietitian… the ‘c’ has *not* been used in decades! ;)

    • Cockhran Polecat

      Is it ok to substitute iceberg lettuce on my double whopper cheese with a big side of leafy stiff green Kale piece? I love burgers n kale!

  • 1PeterW

    Some of us have problems digesting any uncooked raw cruciferous vegetables, e.g. kale, cabbage, broccoli, cauliflower, but steamed, baked, or roasted forms are fine. I have to also wonder if there’s a reason I don’t like the taste of them raw, especially kale. Often there is a bitter taste that’s absent in the cooked form. Is there a genetic preference based on differences? Something not mentioned here but gaining increasing press is biochemical individuality, first publicized by Roger Williams, U of Texas discoverer of pyridoxine, vitamin B6. What can be great for one person can be bad for another.

  • Seattle Coffee Scene

    Damn, kale is bad for you, coffee is bad for you, eggs are bad for you, Vitamin C is bad for you… water in excess is bad for you – I say stop worrying about what is BAD for you.. just eat and drink in moderation – and be happy.

    • Florida Farmer

      Good thing that isn’t the conclusion of all the information in the article.

      • Seattle Coffee Scene

        Yeah, too bad the main point doesn’t lead the article.. or the title…

  • Drew Ramsey, MD

    I appreciate you posting this. It would be a shame if people avoiding eating kale, as there is no known risk to the thyroid and it is one of the healthiest foods a person can consume. Please join the green celebration on National Kale Day October 1! Learn More

  • alexafleckensteinmd

    The goitrogenic substances in cabbages are basically destroyed by cooking. All cabbages have those substances, not only kale. Eating/drinking raw kale occasionally is likely fine. But having a smoothie every single day might create problems.

    The more common cause of low thyroid function in this country are dairy consumption and gluten intolerance. Milk products are highly inflammatory and detrimental for all of us. Gluten is a problem in many people, and has been linked to hypothyroidism.

    Alexa Fleckenstein M.D., physician, author.

    • Samantha Capen Muldoon

      Question – if you steam Kale for a few seconds (or nuke it for a few seconds, or whatever) does that constitute enough ‘cooking’ to destroy the goitrogenic substances? I ask b/c I have a carrot allergy, but only to RAW carrots, so if I nuke them for 5 or 6 seconds, I can eat them. Same with apples. (I know, microwaving things isn’t ideal, but it is better than never eating carrots of apples… and they still stay crunchy that way). Anyway, my husband has a family history of Hashimoto’s Disease, and I was wondering about the Kale/Cabbage issue. Would nuking it for a few seconds do the trick, or do I need to actually steam them until wilted?

      • Chanelle Nadeau Shelburg

        the reason nuking veggies is not “ideal” is that the radiation from the microwaves kills all nutritional value in the veggie… best course of action is to steam the vegetables until they are al dente — or just firm to the teeth… not crunchy

        • Atlantya

          This is totally untrue. Microwaving vegetables does not kill the nutrients.

          • alexafleckensteinmd

            Atlantya, All cooking destroys some nutrients. All cooking makes other nutrients more available. But microwaving does the worst job – every time I tried something from the microwave, I wondered about the beautiful colors , and the totally bland taste. But don’t take my opinion – read up on it!

            Alexa Fleckenstein M.D., physician, author.

          • Atlantya

            Given that you’re both a physician and author, I suggest you start using better research before you pass your (misinformed) opinions on to your patients. I would have hoped someone charged with the health of others would have had better critical thinking skills than this. Also, lack of color and totally bland taste, yes, I had that too until I learned how to cook. With all methods of cooking.

      • I am Incognito

        Season them and bake on a cookie sheet in the oven for 10 minutes at 400-degrees. They are sooooo good cooked that way.

        • Samantha Capen Muldoon

          Oh, I do – delish

      • alexafleckensteinmd

        Not sure there are exact measurements – but Chanelle’s idea to cook them until they are still “al dente” sounds reasonable. All cooking destroys some of the polyphenols we cherish so much in vegetables. But microwaving destroys the most – one study put the number at two thirds of nutrients destroyed by “nuking”. Whereas normal cooking destroys about 30 to 50 percent.

        But raw is not necessarily better: Cooking also makes some nutrients available that are not accessible raw. The best is to cook most of your vegetables, and have a few raw. – Cabbages are not the only vegetables that should be avoided raw; mushrooms contain toxic substances that can cause cancer. Cooking destroys those toxins – in all mushrooms except in champignons (including the dark and white button mushrooms, and portabella). Never ever have raw button mushrooms in your salad!

        And the third thought: Baking kale on a cooking sheet might make a delicious snack: But baking (and broiling, and many other processing methods like drying and pasteurizing) creates Advanced Glycation Endproducts (AGEs). AGEs age you faster, and foster diabetes, cancer and many other metabolic ills.

        Alexa Fleckenstein M.D., physician, author.

        • Tamsen Young

          Michael Pollen argues precisely the opposite….that cooking brings OUT the nutritional benefits in food. hmmm. I tend to trust Mr. Pollen and his research.

          • alexafleckensteinmd

            Tamsen Young, That’s exactly what I wrote in the second paragraph. Looks like you focused solely on my last remark about AGEs. Perhaps I should clarify: OVERDOING the cooking (like baking to a crisp) creates those adverse AGEs particles.

            Michael Pollan is a proponent of slow-cooking at low heat. I agree with him (and you): There is noting better than a braised leg of lamb – once in a while. With tons of fresh vegetables, of course.

            Alexa Fleckenstein M.D., physician, author.

  • Laura Eyring

    I will admit, I have a problem at the end when Dr. Garber strongly advocated for a standard, conventional diet for kids. People seem to think that means soda, junk food, dairy, and lots of meat. Or fast food. Or the food served in the typical public school provided by our wonderful school lunch programs (I hope you can taste the sarcasm from here). I’m no dietician, but I’m guessing french fries on a daily basis is not the greatest food for a growing child.

    But hopefully that isn’t what he meant, and he’s advocating for a healthy diet centered around plant-based foods! I wished he would have gone into it a little bit more, but I understand that isn’t what this article is focused on. Variety is the spice of life, as they say, and eating a variety of veggies has always made sense to me and would seem to address a lot of these issues.

    • Iona Watson

      He didn’t say a standard, conventional diet. He advocated for parents to ” follow standard, conventional nutritional advice for kids,” so you’ve slightly misquoted him, but the nuances in the misquote are important as they lead you to begin with and essentially made a straw man argument. While there’s no denying that the things you’ve listed are unhealthy foods or foods like products, this doctor never said what you accuse him of saying.

    • ThisMom

      “People?” I am a mom, and most other mothers I know feed our children healthy, nourishing whole foods. And many school lunch programs are working hard to provide incredibly healthy offerings – even vegan, gluten-free and the like. Generalities don’t do us much good.

    • Kelly S

      it would never even occur to me that he meant something other than “standard nutritional advice from the medical community.” which is always going to include veggies.

    • I am Incognito

      I roll my eyes every time a new school menu is released. Just shocked that these “dieticians” who plan these menus can possibly think these are healthy meals.

    • Michelle Burnett

      I think you totally misinterpreted what he said to fit the point that you wanted to make. Even parents who are not-that-informed about nutrition know not to feed their kids french fries every day. NO ONE that I can think of believes that an appropriate diet for kids includes “soda, junk food, dairy, and lots of meat.” We get dietary information from our child’s school twice a year encouraging healthy packed lunches and giving recipes (his school doesn’t have a meal program, thank God) and I know there’s nutritional education going on in many school systems. If this was an attempt at trolling, nice job, but your “fears” are unfounded. Thanks for playing.

      P.S. When I Googled “nutritional guidelines for children” this link, from the Mayo Clinic, is what comes up, if that helps ease your troubled mind: The second search result was a page from the American Heart Association.

  • NotApologizing

    It’s difficult, as someone who works in thyroid advocacy, for me to take seriously anyone who endorses the current guidelines for diagnosing and treating hypothyroidism. The current reliance on the out-dated and scientifically unsupported normal range for TSH and the denial of the importance of the Free T3 test in as a screening tool is leaving too many people sick and in need of treatment they aren’t going to get. It’s time to throw out the dogma and look at the new research.

    • TheBride

      I think the mainstream medical community takes a very narrow view of thyroid health and disease. I agree that the testing for thyroid problems needs to finally be overhauled. And I think the problem is that the thyroid has limited potential for big-pharma, so it is not really investigated enough. Not enough drug potential!

      • NotApologizing

        Yup, exactly. The sicker we are, the more money they make on antidepressants, cholesterol drugs, anxiety meds, disgestive aids, muscle relaxers, fibromyalgia meds, etc. etc.