Health Dangers of Cruciferous Vegetables

Health Dangers of Cruciferous Vegetables

Health Dangers of Cruciferous Vegetables

Health Dangers of Cruciferous VegetablesIn our look at the Health Dangers of a Plant-based Diet we turn to the cruciferous vegetables. You might be surprised to learn that broccoli and brussel sprouts have a dark side. I mean these are the vegetables that kill cancer, right? How can there possibly be health dangers of cruciferous vegetables?

Well just like other plants, these vegetables place a high priority on survival. And this means protecting themselves with phytochemicals. The cruciferous vegetables use a special chemical called glucosinolate to deter pests. [r, r] Here we’ll look at glucosinolates and their role in the health dangers of cruciferous vegetables.

Health Dangers of Cruciferous Vegetables – What are they?

Last week as I was walking to perimeter of the grocery store (headed to the butcher) I realized how many vegetables are from the cruciferous family. It’s not just broccoli and brussel sprouts. But it also includes cabbage and cauliflower, kale and collards, radishes and arugula, mustard greens and mustard seeds, and the list goes on.

The crucifers are just like every single plant specie commonly eaten today; it’s vastly different from its pre-agriculture predecessor. We transformed these plants through artificial selection to get the biggest, most pest-resistant breeds possible.

Cabbage, broccoli, cauliflower, brussels sprouts and kale are all different cultivars of a single species, Brassica oleracea. But generation by generation, we engineered this one plant’s leaves, stems and flowers into new “foods.”

You may be familiar with these crucifers because of their pungent smell. It’s the sulfur. And it’s a part of their defense.

Health Dangers of Cruciferous Vegetables – “Broccoli Bomb”

sulforaphaneThe crucifers like broccoli have this chemical called glucosinolate. I like to think of this chemical as the main ingredient of the “bomb.” They also have another chemical called myrosinase. I think of this as the “matchstick” that lights the bomb.

While growing out in a field the bomb and the matchstick sit in separate compartments so that the broccoli doesn’t blow itself up.

But when a little hungry animal comes looking for a snack and bites into the broccoli the bomb gets lit by the match. The explosion that results are bioactive chemicals call isothiocyanates. [r, r] One of the most well-studied isothiocyanate is call sulforaphane.


Sulforaphane is a pungent molecule (perhaps you’ve cooked broccoli and smelled it…) that can deter and kill insects, bacteria, and fungi. It causes cellular apoptosis (cell death). This happens in the cells of these small predators as well as human cells.

If you eat broccoli about 75% of the sulforaphane will be absorbed into the bloodstream and taken up by cells.

Once inside sulforaphane can damage important intracellular structures like mitochondria and enzymes.

The damage increases reactive oxygen species (ROS). And in an attempt to limit the damage, glutathione, our powerful endogenous antioxidant, binds with sulforaphane to get rid of it as quickly as possible (~2-3 hours after eating it). [r] This depletes our glutathione (our most potent human antioxidant) leaving cells vulnerable to further oxidative damage.

Sulforaphane can even disrupt epithelial barriers providing yet another plant chemical that can contribute to “leaky gut.” [rr]

Sulforaphane and Cancer

It’s not surprising that this cell killer has been recognized as an anticancer chemical. It kills cells. Cancer cells and healthy cells. [r, r, r]

Isothiocyanates like sulforaphane trigger the activation of Phase II enzymes. [r] This is like turning up the dial on the human immune system.

For some reason, research paints this in a positive light. Sulforaphane is a hero. Isothiocyanates increase our natural antioxidants. They say it’s a hormetic response. [r] If it doesn’t kill you, it makes you stronger.

I see it through another lense though.

When the body encounters something that is damaging, it wants to get rid of it. To do this it will upregulate an army to fight it. Some of these troops are antioxidants like our friend glutathione. While this is good in the context of fighting a cancerous cell or ridding the body of sulforaphane, I don’t think sending the troops to battle on a constant basis should be seen as a good thing.

The fact that the body puts such a vast importance on getting rid of sulforaphane as quickly as possible suggest to me that it’s more of a danger than a cancer-killing sidekick.

For me, a helpful analogy is to relate to chemotherapy treatment. It is very effective at killing cells. And while the intent is to kill cancerous cells, there is often a significant amount of “friendly fire” and the death of healthy cells as well.

Most people don’t take low dose chemotherapy as a cancer prevention strategy. There’s a reason for this.

Health Dangers of Cruciferous Vegetables – Thyroid Health

goiterThe isothiocyanates created by chewing up broccoli can have potent antithyroid effects and interfere with thyroid hormone production. They compete with iodine and thereby block its uptake by the thyroid. With inadequate iodine there is decreased production of thyroxine and potential for hypothyroidism. [r]

The abnormal absorption of iodine also provokes hypertrophy of the thyroid and goiter. [r]

And it’s not just humans, but animals too.

Oil meals, like rapeseed meal for example, are important protein supplements for livestock. And they are high in glucosinolates. Animals can tolerate up to 5-10% rapeseed meal in their diets before suffering from goiters, depressed growth, gastrointestinal irritation, anemia, perosis, poor egg production, and liver and kidney lesions. [rr]

The high sulfur diet can result in trace mineral deficiencies and polioencephalomalacia, a neurologic disease in ruminants.

Health Dangers of Cruciferous Vegetables – What to do

If you decide to eat cruciferous vegetables, it’s a good idea to take some protective measures.

  • Adding extra iodine to counteract the thiocyanates is helpful. However, additional iodine consumption cannot counteract other glucosinolate byproducts like oxazolidine-2-thiones which also blocks iodine preventing thyroxine production. [r]
  • Avoid sprouts and seeds as they can have orders of magnitude more glucosinolate than matured plants. Plants protect their babies. Eat them with caution.
  • Freezing as well as boiling them can help reduce the glucosinolate concentration (~50%).

Heat actually destroys the myrosinase (the matchstick that lights the bomb); however, the bacteria in our gut can act as the lighter, so sulforaphane will still be produced. [r]

As with other plant chemicals, the poison is in the dose, and an individual’s ability (or lack thereof) to disarm the plant poisons.

An elimination diet (like “Level 3” in the 30 Day Guide to Going Full Carnivore) is a very effective way to determine your ability to handle certain plant foods, which (if any…) are ok, and in what quantity.

[NOTE: You can now access the complete “Health Dangers of a Plant-Based Diet” series here]:

87 Replies to “Health Dangers of Cruciferous Vegetables”

  1. Hi Kevin, Thanks for this article. What are your views on vitamin A and organ meat? Of course most carnivore diets encourage it. But I wonder if yours is different in this respect.

  2. I appreciate your report on cruciferi. I had followed the heard, and was eating them morning, noon, and night. Building up my microbiome. Thanks to your article, I can see that as much good as they may do for us, it is not without a great cost to other aspects of health.

  3. Can I ask what the safest veg to eat is on the carnivore plan? I am on a food plan that means I have to eat a certain amount of veg (12 steps) but I would like to move as closely towards a carnivore plan as possible because of autoimmune symptoms. I had thought: lettuces, radish, squash, cucumber and celery. I wondered if you had any more that seemed relatively low on the toxicity scale?

    Thank you!

  4. So would you say that the supplement Brocco Max would be something that you think could actually cause illness instead of wellness? I appreciate your input if you see this as I did purchase them thinking they might help with liver detox. Thanks

  5. My mother always said, “If the gators don’t get you then the skeeters will!”

    I’m not giving up broccoli cheese casserole and I’m not ever going to like Kale. I was raised as a carnivore as we raised our own cattle and I’m still one. But I love vegetables!! Eat what you want and what you like. Just like those people who are over 100 years old and eat everything. No one gets out of life alive anyways.

    1. It’s not that we don’t LOVE them or WANT to eat them! It’s tolerance! They make us sick! If they didn’t we’d gladly eat them! Happily, joyfully and all that you said! We cannot!

  6. Interesting because the 4 times I have eaten either broccoli or Brussels I wake up with horrible hot flashes and night sweats!! Everyone thinks I am nuts because they are promoted as helping menopause. I have 0 menopausal symptoms when I don’t eat them…..

  7. You mention cooking them. I have read elsewhere that fermenting them makes them safe – eg sauerkraut, fermented Brussels sprouts, etc. Is that correct, to your knowledge?

    1. Yes it can absolutely help reduce antinutrient content – I talk a bit more about this in the full ebook / download too

  8. So what do we need to eat . I am so very confused What is healthy to eat then I have cut out so much trying to get gut healthy!,,, make me a list of what to eat please

    1. Hi Renee, yes, I know it seems like you hear “eat this” one minute and then the next “no that is bad, eat this.”
      I thinking eating in accord to a species / anatomic / physiologic design (like animals naturally do in the wild) is most ideal for humans.
      And I would submit that this is an animal-based diet. That’s the foundation of human nutrition.
      Yes, this diet can be “supplemented” with some occasional (seasonal/geographic/non-GMO/non-super hybridized) whole plant-based foods (i.e. like season, local, organic berries).
      Some people handle various plant-based foods better/worse than others, so the tolerance is obviously variable.
      But the vast plant-based foods that supply most of human nutrition (sugar, grains, vegetable oils) that are the current foundation of human nutrition, I would argue should be eaten minimally, if at all, for optimum human health.

      1. Very interesting ideas. I am of the camp that the body is far more complicated than we’ve even come close to figuring out.
        One thing I have to note is that regardless of all the food theories out there, humans seem to die around the same time. If skipping broccoli expanded life to 140 years, I might say there was some merit to it. But really, no matter what we do, humans eventually get sick and die at certain points
        The premise that we are experiencing unprecedented disease does not really hold true to the context of history, where not long ago, humans dropped like flies at 25-50 because of all kinds of other problems. Despite broccoli, twinkies, & soda, we now live much longer and probably due to greater protection from deadly diseases like polio, etc., better shelters, clothing, abundance of food, etc.

        In short, this is very interesting and I appreciate the contribution! However, I’m not sold that vegetables are inherently dangerous, nor am I sold that the body can’t filter the problems associated with things appropriately. Science nobly tries to prove itself, but is often dead wrong too due to poor study design, asking the wrong questions, etc. Personally, I’m thinking that factors like stress,grief, and resentment will kill you long before broccoli ever will.

        1. Thanks for the comment Anna. And yes, I think when defining “health” just looking at how old one makes it isn’t the best measure in my opinion. My grandmother is currently well into her 90s but has had severe dementia for over a decade.

          Like you mention, life expectancy has increased substantially over the last 200 years, but mostly from decreases in infant mortality as well as success in preventing/treating infectious diseases.
          In the last decade, however, we have seen life expectancy level / decrease, which is complicated and includes increases in drugs-related deaths, suicide, as well as historic rises in deaths linked to influenza (notably in 2017 and, of course highlighted in this 2020 pandemic) but also pneumonia. Health issues that plague us today whether mental or immune or more obviously metabolic (cancer and heart disease which account for nearly half the deaths each year in the US), I believe, can all greatly be improved with better nutrition.

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