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Overdosing on Greens

Raw cruciferous vegetables: how much is too much?

November 3, 2010 |
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From the healthiest beverage to the healthiest food: Dark green leafy vegetables—cruciferous vegetables, cabbage family vegetables, like broccoli, Brussel sprouts, collards, and kale. How could one possibly eat too much kale? Well, there are natural goitrogenic compounds in this family of vegetables that can interfere with thyroid function in people with marginal iodine intake. They can block the thyroid’s uptake of iodine, but the answer is not to avoid these super healthy foods, we just to get enough iodine in our diet, as I’ve detailed in past volumes. Still, though, you can overdo anything.
How much is too much? I specify raw here because an enzyme that releases these compounds is deactivated by cooking so we don’t have to worry about cooked cruciferous, but how much raw is too much? How many cups of coleslaw a day is too much, for example? Five cups a day? Ten? Fifteen? Twenty? Or can you go up to 25 cups of coleslaw a day, every day, for months at a time?
The New England Journal of Medicine: coma induced by raw bok choy. She was eating about 3 pounds a day every day, which means… 15 cups a day is definitely too much. In the two months before she was admitted to the intensive care unit in respiratory failure, she had consumed about a thousand cups of raw bok choy.
Now each cruciferous vegetable has a different amount of these compounds, so you could probably get away with 50—five zero—cups of raw cauliflower a day, but just 3 cups of raw mustard greens a day is too much.

To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring watch the above video. This is just an approximation of the audio contributed by veganmontreal.

To help out on the site please email volunteer@nutritionfacts.org

Dr. Michael Greger

Doctor's Note

Please feel free to post any ask-the-doctor type questions here in the comments section and I’d be happy to try to answer them. And check out the other videos on greens. Also, there are 1,686 other subjects covered in the rest of my videos--please feel free to explore them as well!

For some context, please check out my associated blog posts: The Best DetoxBroccoli Boosts Liver Detox Enzymes, and Nutmeg Toxicity

If you haven't yet, you can subscribe to my videos for free by clicking here.

  • http://nutritionfacts.org/members/veguyan/ Veguyan

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

    • http://nutritionfacts.org/members/mgreger/ 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!

      • http://nutritionfacts.org/members/myjolina/ Laura Scalia

        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?
        thanks
        ps – kale chips are on the way!

        • http://nutritionfacts.org/members/mgreger/ 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.

        • http://jolkapolkaskitchen.blogspot.com/ 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.

  • http://nutritionfacts.org/members/walfaro/ walfaro

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

    • http://nutritionfacts.org/members/mgreger/ 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.

  • http://nutritionfacts.org/members/ananas26/ 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?

    • http://nutritionfacts.org/members/mgreger/ Michael Greger M.D.

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

  • http://nutritionfacts.org/members/mtooles/ mtooles

    Interesting video. I am wondering if you are familiar with the Wahls diet (http://youtu.be/KLjgBLwH3Wc or http://www.facebook.com/pages/The-Wahls-Foundation/150956531629073?sk=app_208412272531040 ) and if so do you believe given the information that you researched that she is recommending too many greens?

    • http://nutritionfacts.org/members/mgreger/ 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.

      • http://jolkapolkaskitchen.blogspot.com/ WholeFoodChomper

        Wow! What a great read.

  • Michael Greger M.D.

    Also, please check out my associated blog post: http://nutritionfacts.org/blog/2012/04/12/the-best-detox/!

  • 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.

  • 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 http://www.jissn.com/content/3/1/51  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.

      • http://jolkapolkaskitchen.blogspot.com/ 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?!

    • http://jolkapolkaskitchen.blogspot.com/ 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

  • 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.

    http://www.hal.inserm.fr/docs/00/47/13/39/PDF/dietary_factors_in_thyroid_cancer_20100308_CCC_R1.pdf