Doctor's Note

Check out these videos for more on cruciferous vegetables:
Prolonged Liver Function Enhancement from Broccoli
The Broccoli Receptor: Our First Line of Defense
Counteracting the Effects of Dioxins Through Diet

And check out my other videos on greens.

For more context, also see my associated blog posts: The Best DetoxBroccoli Boosts Liver Detox Enzymes; and Nutmeg Toxicity.

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  • Veguyan

    Sounds like your assessment of excessive amounts of cruciferous vegetables is based upon one person’s experience. Is that a fair assessment?

    • Michael Greger M.D.

      Though it was a case report (and so by definition described only a single patient), it is consistent with data going back more than 50 years, when researchers in Finland blamed the consumption of milk from cows grazing on cruciferous plants for contributing to the national epidemic of goiter. Don’t get me wrong, I recommend everyone eat greens every day (except those on the drug coumadin who should first ask their physician about re-titrating their dose). Greens are probably the healthiest foods on the planet–but a thousand cups is too much!

      • myjolina

        Can you explain further why the drug coumadin would react with kale. If someone has too much iron in their blood, haemochromotosis, would they suffer from eating kale. Is there an immediate reaction to too much kale or is it a slow build-up in the blood system that would create symptoms?
        ps – kale chips are on the way!

        • Michael Greger M.D.

          Great questions–seriously! One can eat dark green leafy vegetables while one is on Coumadin; one just has to titrate their greens consumption to their Coumadin dose. Coumadin (a.k.a. warfarin, a.k.a. rat poison) is a blood thinner that works by interfering with the action of vitamin K. So if all the sudden you eat lots of greens (excellent sources of K) you can overwhelm the drug’s ability to keep it from clotting your blood normally. So we should all be eating lots of greens; folks on coumadin just need to keep their greens consumption relatively stable and make sure their physician matches that level of consumption with the appropriate dose. Or even better, one can eat a healthy diet and help avoid the kinds of conditions (like heart attacks) that might lead to one having to take these sorts of drugs in the first place! :)

          And no, one does not have to worry about plant-based sources of iron in terms of iron overload since your body is able to restrict absorption. Blood-based (“heme”) iron is absorbed whether our body likes it or not, however, and can indeed contribute to the development of that iron overload disease in susceptible individuals. Eat your kale! More about iron here.

          And I can’t wait for the chips! For those that missed it, I’m offering to mail a complimentary copy of my latest DVD to anyone who sends me (address here) their very own homemade kale chips–now that’s what I call veggie booty! :)

          • JoAnn Downey Ivey

            The oven is on! Seriously Dr. Greger, I’ve been on Synthroid for 30 years (since age 37) so do I need to worry about iodine and thyroid function? I’m well controlled on medication. I don’t do salt, so my source of iodine is what’s in the liquid from Eden Organic NAS beans. Thanks.

        • WholeFoodChomper

          I have yet to make kale chips successfully. Can anyone direct me to a good reliable and tasty recipe?

          • Rebecca Johnson

            1 C raw cashews
            1 red bell pepper
            1 small/roma tomato
            1/8 cup lemon juice
            1/4 C nutritional yeast
            1/8 tsp salt or to taste
            pepper to taste

            Blend in high-speed blender. Coat kale leaves with blended mixture. Dry in dehydrator.

            Adjust all ingredients to your taste – e.g., if you like it tangier, use more lemon juice.

  • walfaro

    Dr. Greger: Do you consider 10 cups of cruciferous to much at day? Is there a link between them and inflammation?

    • Michael Greger M.D.

      According to this study published in the Journal of the Science of Food and Agriculture, 10 cups a day on a regular basis is probably the limit for raw kale–my second favorite vegetable!

      • Laurak

        Please tell what is your favorite vegetable? You can’t leave us hanging!! Also is that cooked or raw?

      • Zany

        I would also like to know why kale is not your favorite vegetable and what is?

      • Sebastian Tristan

        According to the Agricultural Research Service of the U.S. Department of Agriculture database, 10 cups of kale is like 670 grams. I double any human can eat so much on a daily basis.

  • ananas26

    I just “discovered” your site ! really enjoy the videos.
    It just made me think of all the euphoria there is with drinking green smoothies and juices lately ( which I love) how much is too much kale for example in one day?
    and will doing a one month or two month juice fast for example be harmful in the long run if too many greens are used?

    • Michael Greger M.D.

      Please see my kale response to walfaro immediately above–thanks for your question!

  • mtooles

    Interesting video. I am wondering if you are familiar with the Wahls diet ( or ) and if so do you believe given the information that you researched that she is recommending too many greens?

    • Michael Greger M.D.

      I’m not familiar with Dr. Wahl’s dietary recommendations, but I liked her recent commentary on self-empowerment in the Journal of General Internal Medicine (one of my favorite journals): The Seventy Percent Solution.

      • WholeFoodChomper

        Wow! What a great read.

      • aballiett

        This link is dead. Do you have another? Thanks!

  • Michael Greger M.D.

    Also, please check out my associated blog post:!

  • Michael Greger M.D.

    Please check out my associated blog post, The Best Detox!

    • Ellen Scarisbrick

       My husband and I have begun drinking green smoothies containing raw kale…maybe 1/2 a bunch or more in the vitamix along with fruit to make it more palatable. We really feel this is a easy way to get greens consistently into our diet. By the way, we are totally convinced that whole food, plant-based is the healthiest form of diet. No need to convince us of that. My question is, since my husband (age 71) is on thyroid medication should he avoid completely all forms of raw cruciferous vegetables?

      • Toxins

        Certain veggies, especially the cruciferous veggies, contain natural chemicals called goitrogens that can interfere with thyroid hormone synthesis. Other foods that contain these chemicals include corn, sweet
        potatoes, lima beans, turnips, peanuts, cassava, and soybeans.

        Most of these goitrogens are not of any real significance unless they are consumed in very large amounts or there is coexisting iodine deficiency. So, while it is theoretically possible for someone to consume enough of these foods that they may have an effect, for most people it is not an issue. However, when consumed raw, as part of a smoothie, there is the possibility of there being an impact from them, especially if the person
        is consuming several of these smoothies a day. These goitrogens are inactivated by cooking, even by light steaming, so
        there is no need to forego them when consumed in that style.

        • dorange

          Rami, are goitrogens in soybeans and sweet potatoes, etc. also inactivated by cooking? How about peanuts, which are not steamed, but roasted?

          • Rami Najjar

            Generally yes, but this is only a concern for those with pre existing thyroid conditions. I would not worry about it otherwise.

          • Mule4eva

            Goitrogens are chemicals in food such as kale, cruciferous vegetables and soybeans. Many, but not all, green vegetables contain some levels of goitrogens. Even when eaten frequently, foods containing goitrogens will not cause thyroid disease in healthy people. You need only monitor goitrogen intake after you have been diagnosed with thyroid disease. Kale and green vegetables are very healthy foods, rich in nutrients, and do not need to be avoided completely. If you have thyroid disease, continue to eat these foods cooked. Dietary guidelines given by your doctor should take precedence…..Mr. Ghandi

          • Rami Najjar

            You have echoed my response

  • Drbill

    Dear Dr. Greger,
    Thank you for the brilliant posts on this subject. Several years back I published a paper [Food Alone May Not Provide Sufficient Micronutrients for Preventing Deficiency] open access  I performed diet analysis on 10-men & 10-women according to actual weighed foods they consumed over 3-7-day periods. None of the 20-healthy subjects were consuming near the reference range iodine levels. It was the only micronutrient 100% were deficient. I declare 20-healthy randomly chosen subjects do not represent the whole. It is this note that asks if the potential cause for many disease have a dietary component complexly resulting in hypothyroidism in large populations?
    We would enjoy hearing your view…
    Bill Misner

  • vademonbreun

    Please research the Gap’s diet for clearing up adrenal and thyroid related issues!!

    • Dr. Connie Sanchez, N.D.

      There has been no scientific studies/research done on the GAPS diet. Any evidence that it “clears up” adrenal and thyroid issues is purely anectdotal. 85% of the GAPS diet is made out of meats, fish, eggs, fermented dairy and vegetables (some well-cooked, some fermented and some raw). This diet is too high in saturated fat and cholesterol to be healthy.

      • WholeFoodChomper

        Good point Dr. Sanchez, but I think that vademonbreun is saying what you are (to a point) that there are no scientific studies on the GAPS diet, and that someone should conduct some studies to determine its effects on adrenal and thyroid health.

        I, for one, wish that there were a site similar to this one on thyroid health. From my few forays into researching thyroid health it seems that, just like in the health and wellness nutrition field, there is a lot of bunky claims being made often to people who are quite desperate for relief.

      • Joonyaboy

        It frightens me that doctors are still afraid of saturated fat (the healthy kind). I lost 50 pounds and all my health markers increased when I started consuming fat for 70% of my daily diet. Please don’t go off what you learned in school. Take some time to research.

  • Guest

    Dr. Greger, is there any danger in consuming too much greens because of vitamin K. Almost all green leafy food easily contain daily dosages – and vitamin K is said to have an impact on blood clotting..

  • steff

    My husband and I recently depressed our thyroid function by juicing a large handful of fresh kale from my garden every day with our smoothies. After 4 or 5 weeks of daily juicing we began to lose energy and stamina, and developed brain fog. When we complained to our primary care doc he drew blood and discovered that our TSH was high and free T4 was low. I should mention that we didn’t have much iodine in our diets. We started eating dulse and a little seaweed salad every day for iodine and left off the kale–we are recovered now after about a month….who knew?!

    • WholeFoodChomper

      Wow, That must have been quite the experience for you guys! Glad that you were able to adjust your diet and recover rather quickly it sounds like.

      As someone with Hashimoto’s Thyroiditis, I have read that raw kale and other raw cruciferous veggies can have goitrogenic effects on the thyroid (the ability to cause a goiter and slow down the thyroid, much like anti-thyroid drugs do), and can even affect the absorption of synthetic thyroid hormone medicaiton. Apparently, raw juicing goitrogenic vegetables ends up providing especially high concentrations of goiter-promoting ingredients.

      Luckily, I have also read and been informed that the enzymes involved in the formation of goitrogenic substances in some plant foods can be partially destroyed by heat. Which is a good thing b/c that means that these yummy health foods can still be eaten if they are steamed or cooked. And, even in moderation in there raw form.

    • Sebastian Tristan

      How much kale did each one of you have daily?

  • Ирина Счастливая

    Почему без титров? =( печаль какая то выходит

  • Gayle Delaney

    Can an overdose of raw cruciferous vegetables (kale, collards, etc.) in smoothies cause the feeling of serious acid-burn tongue similar to same from overload of raw pineapple, but lasting for a week? Is there any ingredient we could add to the smoothie that would neutralize this effect? Any cure besides the tincture of time and time off those smoothies?

  • NHGirl

    Hi, Dr. Greger,
    I recently adopted a whole, plant-based vegan diet after years of reading the research. However, I have Hashimoto’s Disease and regularly take levothyroxine to mitigate the effects of this. Lately, my TSH levels have gone back up — have you seen any evidence to suggest that the addition of raw greens in smoothies could produce this? I am also a green tea drinker in the morning and am wondering if this could all be interacting. Any advice you may have to give would be greatly appreciated!
    Thank you,
    NH Girl

    • sf_jeff

      ctrl-F search on this page for “TSH” the answer is, more Iodine and cook or skip certain veggies.

  • D

    When I vitamix-juice, I juice 1 pound of spinach, 1/4 pound of kale, 1-1.5 pounds of berries and sometimes add chia seeds and/or parsley. I drink this over about 8-12 hours. Is this too much?

  • Carrie

    So, Dr. Greger, would you recommend against drinking raw kale juice regularly? Thank you.

  • Cgillenator

    dr. Greger, I currently am on armor thyroid, since I had a complete thyroidectomy ten years ago. Just started sprouting broccoli and i eat a lot of homemade kale chips. do you see a problem with eating about a quarter cup of broccoli sprout and a cup of kale chips a day. I have a great recipe for kale chips which includes miso, nutritional yeast and turmeric.

  • Rob Dodd

    I juice daily, so always add a double handful of kale, spinach or another leafy green veg. I
    read somewhere that revolving your cruciferous vegetables can minimise
    any side effects, so I use a different handful every day. But it seems I could be wrong! I must check on your iodine posts.

  • Celine Indiana

    If 10 cups of greens is ok, does it matter wether it is juiced or eaten as a salad or steamed?

  • Mindaugas Raulinaitis

    The study included 293 cases of thyroid cancer and 354 population controls. We found that high consumption of cruciferous vegetables was associated with thyroid cancer among women with low iodine intake (OR=1.86; 95% CI: 1.01-3.43 for iodine intake < 96 µg/day). The high consumption of cruciferous vegetables among Melanesian women, a group with mild iodine deficiency, may contribute to explain the exceptionally high incidence of thyroid cancer in this group.

  • Travis H

    I am hoping you can provide more info on which plants contain more of these compounds than others… My wife loves arugula what would the daily limit be?

  • Paul Oakes

    Thank you, Dr. Greger, for your contributions here on Great stuff. I’ve been consuming one or two small bunches of watercress daily since I read about how it helps with exercise recovery. How much watercress would be too much? Would eating dulse seaweed help balance it’s goitrogenic effect?

  • Guest

    Can you tell me if there are any true studies showing the danger of too much kale comsumption and excessive thallium intake?

    Please see link below pertaining to the idea:

    Thank you!

  • Carol

    I started using the dark greens in the nutribullet for three weeks running. About two large cups a day. My breathing started to get very poor, almost like I was caught for breath. I’ve had my thyroid checked with my gp but she said it’s seems to be fine and the breath test was fine and high. I’ve backed off using any greens except fresh mint for now. Waiting for my breathing to correct itself still. Is this usual do you know? Thanks.

  • 4Baccurate

    I wonder if it is the sulforaphane that inhibits iodine uptake by the thyroid gland? Is sulforaphane’s effectiveness reduced by cooking? Thanks!

  • nmi1010

    Instead of 55 cups a day, would like to know about reasonable amounts of raw cruciferous vegies and thyroid and how much iodine to counteract effects if you’re a vegan. (Following your daily 12.) Especially if you have borderline low thyroid. Many thanks!

  • tyty

    Hey, medical question.
    Im 26 , female, and have had chronic constipation for well over 7 years (and even before that wasn’t regular), most of the time I need to take suppositories as oral laxatives
    I’m being tested for hyprothyroidism (waiting for results), I eat a 100% whole food plant based diet (and vegan for 3 years), plenty of greens etc everyday. I was looking up any diet related intervention to help with hypothyroidism and constipation…trouble is I either get told to eat more fibre ( lol, my diet IS fibre) or cut out lots of amazing foods like spinach, cauliflower etc, and i’m wondering if my large intake of fruits, beans, nuts, greens and veggies are making my condition worse.
    what advice would you suggest? Not sure I can take another doctors appointment where they throw another unhelpful and chemical ridden laxative at me.
    thankyou for your time!

  • passthebeans

    Hello, I have not been able to find any information from your website on Hashimoto’s Disease. I guess what l would like to know is making the change to a plant based diet, can l be hopeful that my auto immune disease be treated and possibly get off the Thoroxine that l am currently on?

    • Thea

      passthebeans: I don’t know if there are any specific studies on Hashimotos and diet or not. But here’s a thought for you: Eating a diet of whole plant foods has helped lots of people with various auto immune diseases. Seems worth trying. Furthermore, even if you were not able to get off the Thoroxine, switching to a healthy diet would help keep you healthy in other areas of your life so that your life doesn’t get even more complicated by other health issues. Something to think about. Would you like some pointers to resources that help people make the change?

  • passthebeans

    Thank you Thea for the heart warming advise, l have been following a plant based diet of veg, fruit, nuts, seeds, beans and mushrooms for nearly 4 months now. I have experienced the plant based diet to be more beneficial. Perhaps some time in the future l maybe able to answer my own questions.

    • Thea

      passthebeans: Keep us posted. I’m thinking good thoughts for you.


    I lost my teeth due to bone loss (undiagnosed Diabetes). I did get dentures, but they never fit well, plus I couldn’t get past that plastic (?) piece that goes between the right side and left side of the upper denture. It made me gag, and no matter how much I did try, I just couldn’t tolerate it. I would love to get the new complete “denture” implants. But there’s no way I could ever afford it. Not even with a payment plan. I love raw vegetables, but obviously can no longer eat them. So, I have to cook them to “death”. So, there goes the nutrition of the food. Even if you only steam them. So I’ve opted to juicing. I haven’t started yet. I did buy a slow masticating juicer. Able to handle everything I want to incorporate into my new eating lifestyle. Everyone is concerned with my wanting to go on a 30 day juice fast, followed by juicing all the time and limiting the solid food I eat. My plan is simple; go on the green juicing diet for the 30 days, and then start incorporating beans, nuts, and of course only eating organic. My neighbour has a large veg. garden every year, but she doesn’t eat the veggies, I do. I think I’ve got her talked into doing it for me; her: short term to detox, but she say’s she couldn’t ever give up meat. I’m not going to eat meat or dairy, I hope. I must confess, I’m going to have a problem giving up yogurt. Perhaps I can make my own @ home from organic milk/cream (?), whatever it takes to make it. I am also going to learn how to “can” fruits and veggies. This way I’ll have them when fresh (organic) is not available in the store. Options ? , opinions ? , answers ? Thanks, Jolae


    I forgot, juicing will be better for me than what I have been doing. Food wise. That’s why I don’t understand the concern. Jolae


    Is there any diet cure for low thyroid.