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Overdosing on Greens

Raw cruciferous vegetables: how much is too much?

April 21, 2011 |
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Overdosing on Greens, 4.7 out of 5 based on 3 ratings

Sources Cited

N Engl J Med. 2010 May 20;362(20):1945-6. Myxedema coma induced by ingestion of raw bok choy. Chu M, Seltzer TF.

Acknowledgements

Transcript

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

For some context, please check out my associated blog post, The Best Detox.

  • 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! :)

  • 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?

  • 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.

  • 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.

  • 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..

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