Doctor's Note

More on broccoli cooking methods and nutrient absorption:
Second Strategy to Cooking Broccoli
Sometimes the Enzyme Myth Is True

And for more on the protective properties of broccoli:
Sulforaphane: From Broccoli to Breast
Raw Broccoli and Bladder Cancer Survival
The Broccoli Receptor: Our First Line of Defense
DNA Protection from Broccoli
Prolonged Liver Function Enhancement From Broccoli

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  • Veguyan


  • Thank you, Dr. Greger! Great information! I was confused by a study I read
    “A critical review of the bioavailability of glucosinolates and related compounds” which stated: “Mastication of the raw or processed vegetable is the first step that is likely to release intact GLSs and myrosinase to form GLS-HPs. The exception are microwaved vegetables, in which myrosinase activity is completely abolished.” (p. 434 under Mastication) Is this true?

    • Michael Greger M.D.

      Ooh, great question! The same thing happens with all cooking methods. The enzyme is denatured (inactivated) but the glucosinolates themselves remain intake (in other words are heat stable). So that’s why it’s actually a good idea to chop broccoli and other cruciferous (cabbage-family) vegetables 20 minutes or so before you cook it to maximize your intake of these wonderful compounds. The same actually goes with garlic, for a similar reason. Check out Becoming Raw from your local library for more info, though now that you mention it maybe I should make a video about it!

  • Thanks for your answer! I’m aware that it is good to chop crucifers first – which, of course, begs the question of how MUCH chopping and how many nutrients we are leaving on the table by a rough chop. Blend everything? Sigh. A video on this would be great!
    Sorry to push the issue but the study seems to say that microwaving is never a good way of cooking these vegetables. Is this conclusion borne out by other studies? I’m a little confused.
    This is the study:

    From the study:
    “GLS hydrolysis during mastication of thermally processed Brassica vegetables (cooked or microwaved) depends on the processing conditions. The latter determine the degree of cell disruption, the activity of GLS degrading enzymes and possibly the activity of ESP. A high degree of thermal cell disruption enables an extensive release of GLSs. Myrosinase is relatively heat stable and may survive blanching or even boiling of the plant material while ESP is heat sensitive, and the effect of thermal processing on nitrile formation is not clear. If myrosinase remains active after processing, this provides optimal conditions for enzymatic GLS hydrolysis and high yields of the corresponding GLS-HPs. In contrast, microwave cooking is extremely efficient at inactivating myrosinase.” BTW – there were no footnoted references for these statements.

    • Michael Greger M.D.

      Sorry I wasn’t clearer. The myrosinase is the enzyme I’m talking about. If you prechop, the enzyme has a chance to do it’s job and so then can be completely inactivated by whichever cooking method and we still get the preformed glucosinolates (the liver detoxification boosting compounds) into our system. My favorite source, though, is broccoli sprouts, which you can make yourself and always fresh produce at hand for pennies a pound!

  • fjansen

    Dr. Greger, this is really eye opening information. Thanks for posting. I do have a question, how does steaming broccoli compare to blending raw broccoli?

    • Toxins

      Hello fjansen!
      To answer your question, it seems it doesn’t matter how thoroughly you blend it up or chew it, you don’t get as much nutrients as you would steamed. please view Dr. Greger’s video on raw food nutrient absorption for further detail:
      For example, four times the lycopene is absorbed in the tomatoes when they are cooked no matter how blended up they are raw.

  • Sujatha

    I’m also curious about whether juicing gives you more of a “raw” or “cooked” product, in terms of nutrition.

    • Toxins

      Hello Sujatha,

      Please see this video discussing juicing!

      • Gabrielle

        That vid you linked to is about fruits, not veggies.

    • Gabrielle

      I think it still counts as raw if there is no heating involved, but I may be wrong. I just see it as a juice version of the original product. If your juicing the food yourself you wont have to worry about harmful ingredients being added like extra sugar or salt or artificial sweeteners.

  • Sabre

    About 5 years back the Australian Consumer Association “Choice” magazine reported that various studies demonstrated that microwaving veggies destroyed 90% of antioxidants compared to steaming (10%). Few now use microwaves for veggies.

    Here is another quote from ‘Health Day’

    “The first study found that the simplest cooking method was also the worst when it came to preserving nutrients. Broccoli lost 97 percent of flavonoids, 74 percent of sinapics and 87 percent of caffeoyl-quinic derivatives (three different types of antioxidants) when it was microwaved.

    When boiled the conventional way (i.e., not in a pressure-cooker), this green lost 66 percent of its flavonoids; when tossed in a pressure cooker, broccoli lost 47 percent of its caffeoyl-quinic acid derivatives.

    Steamed broccoli, on the other hand, lost only 11 percent, 0 percent and 8 percent, respectively, of flavonoids, sinapics, and caffeoyl-quinic derivatives.”

    The underlying theory was that microwaves induce the rapid vibration of the fluidic molecules inside the plant and so destroy the molecular structural integrity of the vitamins and antioxidants.
    Someone has it badly wrong here, but who?
    It probably depends on which molecules are being tested.
    Is there any definitive evidence here yet as there is a huge disagreement on this important issue?

    • Toxins

      Sabre, I have read articles that will twist studies around sometimes. If you could please post the studies themselves (or atleast the references) then we can scrutinize both sides.

  • Jo

    Hi Dr. Greger,

    I hope you can clear this up for me. In regards to sulforaphane in broccoli …  I understand steaming is the best way to absorb and boost broccoli’s nutrients, but is this true of the cancer-fighting sulforaphane? I tried finding the answer online, but keep reading conflicting reports.Should we continue to eat broccoli raw or start steaming to get the most sulforaphane?

    • Toxins

       Hi Jo,

      cooking does in fact inhibit sulphorophane creation under the condition that you do not chop your vegetables before hand. If you chop the broccoli then the sulphorophane is retained.

  • Ronald Chavin

    The fact that absorption of nutrients is a little worse when eating broccoli raw is not necessarily a disadvantage. The beneficial lactobacilli, which thrive on the surface of green vegetables, are killed by the steaming or microwaving. Also, the part that we fail to absorb becomes food for the beneficial bacteria, which they ferment to manufacture many beneficial chemicals, including propionate, acetate, butyrate, and lactic acid, which inhibits the bad bacteria by attacking them with hydrogen ions (acid).

  • Add to the analysis blending raw broccoli leaves in a powerful blender so that better physical breakdown occurs.

  • extremefruitboy boutdatrawlyfe

    What was the temperature setting when microwaving? Anyone with full access to the article please clarify.

  • Pierre Gregory

    So where is the question about roasting nuts that begins this video answered? I’m curious about raw vs roasted nuts and nutritional values/bio-availablity studies.