Whether you’re talking broccoli, cauliflower, or kale, it is true there’s a side effect of eating them.

But this common side effect – and how to fix it – is not what people are talking about.

Instead, the hysteria revolves around hyperthyroidism. The theory that eating these veggies will cause that butterfly-shaped gland at the base of your neck to produce too much of the thyroid hormones.

On the flip side, you have those touting anti-cancer benefits for broccoli and others.

With conflicting messages, what is one to do?

Representative species

First off, let’s make sure we are all talking about the same thing.

Is spinach a cruciferous vegetable? Nope. Whether it’s regular or baby spinach, it’s a member of the Amaranthaceae family, which is non-cruciferous.

For a vegetable to be cruciferous it has to come from the Brassicaceae family, which is also called Cruciferae and hence the name.

heads of cabbage, cauliflower and romanesco broccoliThere are over 4,000 species in the Brassicaceae family, but this list of cruciferous vegetables is for the most commonly consumed:

  • Arugula (Eruca sativa)
  • Bok choy (Brassica rapa)
  • Broccoli (Brassica oleracea, variety italica)
  • Brussels sprouts (Brassica oleracea, variety gemmifera)
  • Cabbage (Brassica oleracea, variety capitata)
  • Capers (Capparis spinosa)
  • Cauliflower (Brassica oleracea, variety botrytis)
  • Collard greens (Brassica oleracea, variety acephala)
  • Kale (Brassica oleracea, variety acephala)
  • Maca root (Lepidium meyenii)
  • Mustard greens (Brassica juncea)
  • Napa (Brassica rapa, variety pekinensis)
  • Rapeseed (Brassica napus, variety napus)
  • Rutabaga (Brassica napus, variety napobrassica)
  • Turnip (Brassica rapa, variety rapa)
  • Horseradish (Armoracia rusticana)
  • Radish (Raphanus sativus)
  • Rocket (genus Sisymbrium)
  • Sea kale (Crambe maritima)
  • Watercress (Nasturtium officinale)
  • White mustard (Sinapis alba)

That last species on the list is used to make yellow mustard. It’s made by grinding the seeds. Brown mustard is made from the seeds of mustard greens (Brassica juncea).

Thanks to the mustard, even a Big Mac contains a vegetable that’s cruciferous!

Of course, the purported cancer fighting benefits – or thyroid harming side effects – are not going to be happening from a little dollop of French’s!

Is kale bad for thyroid?

diagram of human thyroid gland anatomyEating too much kale or other types have not been linked to hyperthyroidism, but rather hypothyroidism. That’s when the gland is not producing enough of the hormone triiodothyronine (T3) and its prohormone, thyroxine (T4). Both of these are linked to the regulation of metabolism.

This sounds scary, until you dig deeper into the facts:

  • Hypothyroidism was observed in an animal study, not healthy humans. (1)
  • In humans, the only evidence of it potentially being a problem is when an iodine deficiency is present. (2)
  • The myth that cruciferous vegetables cause cancer in healthy individuals can be debunked using a 2015 meta-analysis of 18 different studies. Yes, high intake did correlate with increased risk of thyroid cancer, but only when the patients were iodine-deficient. For those with normal iodine levels, there was no increased risk. (3)

So what’s the link between cauliflower, iodine, and your thyroid?

Glucosinolates are the reason. These sulfur and nitrogen containing compounds are almost exclusive to the Brassicaceae family. That pungent taste from horseradish and mustard comes from these compounds.

When the glucosinolates are broken down during digestion, two of the compounds released are goitrin and thiocyanate ions. Due to their size and shape, these can compete head on with iodine for absorption. As a result, the gland may absorb too much of those and not enough iodine, which is an essential mineral.

But they’re also good for thyroid…

For those at risk of iodine deficiency, it’s unfair to categorize all cruciferous vegetables as being bad for you.

Recent research has found that Brussels sports, rapeseed, and collard greens have enough goitrin to interfere with iodine absorption.

fresh broccoli

Don’t demonize broccoli the same as Brussels sprouts.

However broccoli (including broccoli rabe), turnip tops, and kale all contain less 10 micromoles of goitrin per 100 gram (3.5 ounce) serving.

It has been reported that 194 micromoles will interfere with absorption, but not 77. In other words, broccoli and kale only have about 1/7th the amount of goitrin per serving that’s needed to interfere with iodine uptake. (4)

In plain English, these superfoods only contain a tiny amount which “can be assumed to have minimal adverse risks for thyroid health.”

So rather than give up these veggies entirely, these endocrinologists at UCLA and the VA Health System imply it’s about choosing the right ones, in the right amounts, so the reported anti-cancer benefits can still be reaped:

“Components of brassica vegetables demonstrate important anticarcinogenic properties that must be balanced…”

Are you at risk?

On average, 35% of the world’s population has insufficient iodine intake. That’s defined as urinary iodine (UI) testing below 100 µg/L, according to the World Health Organization (WHO). (5)

In the United States it’s less common. The WHO lumps together South, Central, and North America as one region. For those areas, it’s 9.8% who are deficient.

Now it is true that iodine deficiency rates are on the rise in the US, Europe, and the developed world. By some estimates, deficiency rates have increased 4x during the past 4 decades. (6) (7)

fancy gourmet saltWhy? It’s not that we don’t eat enough salt, we actually eat way too much. Rather it has more to do with the fact that much of the salt being sold today does not have iodine added to it.

Sea salt and gourmet Himalayan pink salt may be all the rage for trace minerals, but they don’t have iodine added like that old fashioned cardboard tube of Morton iodized salt.

Fancy salts aside, many of the plain table and commercial varieties have also stopped with fortification.

The deficiency risk may be growing, but there is not evidence of cruciferous foods contributing to the problem in healthy individuals.

Even though Brussels sprouts are one of the vegetables highest in glucosinolates, after a study in which participants ate over 5 ounces per day for 4 weeks straight, there were no changes observed in the production of T3 and T4 hormones by their thyroid. (8)

The rebuttal would be that Brussels sprouts are always cooked and that largely destroys their glucosinolate-degrading enzyme, myrosinase.

That is true and veggies like kale, cabbage, and arugula are often eaten raw as part of a salad. So yes, you can’t really compare the risk between cooked vs. raw.

Ultimately though, this just lends more justification as to why you should be taking a good daily multivitamin regardless.

You should use an organic whole food based multi. Not the crappy Centrum, Nature Made, or One-A-Day. Those contain synthetically created vitamins and with some, artificial colors and chemicals like polyethylene glycol.

Here at Superfoodly, the brand we buy ourselves is Garden of Life’s mykind organics line.

vitamin supplement facts label showing iodine in it

Pictured above is the label for their 2x per day multivitamin for men. Taking one at breakfast and another at dinner is the best way to do it – it keeps more stable levels of vitamins and minerals in your system. On Amazon you can get the men’s and the women’s version for a good price.

Both offer 100% of your daily value for iodine and it’s derived from an organic food blend, not mined minerals and chemicals.

Getting your RDA of iodine from iodized salt (i.e. Morton) would be a terrible idea.

In an ideal world we could do that, but adding even more salt to your diet doesn’t work today, because literally everything you buy already has too much added (and often it’s the non-iodized form).

Yes, salt (sodium) is an essential mineral, but what people don’t understand is that there’s already enough in what you eat. All plants, dairy, and meats already contain it, even before any salt is added.

If you think you’re safe because you’re buying natural, organic, and “healthy” foods, think again.

bags of Rhythm kale chips for sale at Erewhon storeWhen almost every single sandwich on their menu exceeds the American Heart Association’s recommended limit for daily sodium intake, is Panera healthy? Even the most popular brand of kale chips sold in America has more sodium than what you will find in a large order of McDonald’s fries!

In many instances, the foods marketed as “healthy” have higher sodium than those thought of as junk food. Just compare Chipotle vs. McDonald’s. The one that’s way worse than the other is not the one you would expect!

Because our society adds salt to everything, we are wreaking havoc on our cardiovascular system, which contributes to not just heart disease, high blood pressure, and neurodegenerative conditions, but also inflammation throughout your entire body. Inflammation plays a part in almost every disease known to man and even contributes to signs of aging. (9)

Benefits of cruciferous vegetables

Is it the antioxidants? Nope. According to ORAC testing, how much antioxidants there are in cruciferous plants is only average, at best. Here are the ORAC values for some of the common representative species in your diet:

  • Cabbage = 529
  • Cauliflower = 870
  • Brussels sprouts = 1,330
  • Broccoli = 1,510
  • Kale = 1,770
  • Arugula = 1,904
  • Broccoli rabe = 3,083
Indian gooseberry (amla) on tree

What an amla looks like.

Now compare those values to these other foods…

  • Fresh oregano = 13,970
  • Fresh marjoram = 27,297
  • Fresh sage = 32,004
  • Cocao powder = 55,653
  • Acai powder = 102,700
  • Dried oregano = 175,295
  • Dried amla fruit = 261,500

Now those aren’t even the highest foods, they’re just a sampling of hundreds which have more antioxidants than even organic and raw kale.

As you see too, the differences are profound. When comparing equal weights of each, rather than eat broccoli, you can eat dried amla fruit and get 17,000% more antioxidants.

But guess what? That doesn’t matter, because antioxidants are not the most impressive benefit of the Brassicaceae family.

Nor is it the vitamin and mineral content. Yes, these mean greens pack a lot of ’em – especially the hard-to-get vitamin K needed for bone health – but that still isn’t their most noteworthy trait.

While some byproducts of some glucosinolates are problematic for iodine absorption, these compounds have demonstrated a unique cancer combating activity in numerous pieces of research. No other category of veggies has demonstrated such a potential. Not even the high ORAC foods.

If you search the NIH PubMed database for cruciferous vegetables and cancer, you will get back nearly a thousand pieces of medical research. Among them, 44 happen to be clinical trials. There is an overwhelming amount of evidence to suggest that these plants might offer some preventive benefits for numerous types of cancer.

For example, take a look at the study from the University of Quebec. Using cultured cancer cells, they tested various types of veggies to see if they helped to prevent or slow down the cell growth (antiproliferative). (10)

It’s not like they tested one type, either. Stomach, pancreatic, brain, lung, kidney, and breast cancer cells were all evaluated.

The following chart was how the lung cancer cells responded in vitro (in the lab):

antiproliferative activity of cruciferous vegetables

After testing all of the difference types of cancer cells, only 8 vegetables were found to have an overall “very high” inhibitory effect and half of them were of the cruciferous type; Brussels sprouts, kale, cabbage, and curly cabbage. The others were of the genus Allium (garlic, leek, green onion) and Spinacia (spinach).

So why did the cruciferous seem to inhibit the growth of cancer cells? Here was their answer:

“This inhibitory effect is most likely related to the content of these vegetables in glucosinolates…”

That’s right, what causes the raw cruciferous vegetables’ thyroid suppression is among the same class of compounds responsible for the purported anti-cancer effect.

Of course, nutrition and what goes on inside the human body is difficult to measure. Especially for something like cancer, which is a slow progressing disease during the early and undetectable stages. Brain tumors can take up to 30 years to form. For breast cancer, you won’t even be able to see it on a mammogram for an estimated 6 to 8 years after the first cell mutation which caused it. (11)

That’s one of the things which makes cancer research so difficult. Determining whether or not a given food might offer preventive benefits is a decades-long process. A lot of time is needed, as well as money and participants.

Until those types of studies are conducted, no one can say the antiproliferative benefits of broccoli, kale, and so forth are proven. Maybe they’re not the real deal.

That being said, given the large body of research suggesting this potential and their relative safety (as long as you have a healthy thyroid) it seems foolish not to adapt these veggies are part of your daily diet.

The problem with cooking them

In tests using rapeseed meal, it was found that the glucosinolates decreased by the following percentages: (12)

  • microwaving for 2.5 minutes = 7.0-25.4%
  • drying at 140°F for 6 to 12 hours = 36-90%
  • fermenting at 86°F for 2.5 to 4 days = 100%

Even at relatively low cooking temperature like boiling, it has been found that the heat destroys the glucosinolates. Here’s how much was destroyed in rapeseed meal as it was cooked. (13)

Temperature Time Cooked Decrease In Glucosinolates
100°C (212ºF) 15 min 24%
100°C (212ºF) 30 min 46%
100°C (212ºF) 60 min 70%
100°C (212ºF) 120 min 95%

The takeaway? If you want to get the glucosinolates, your cooked Brussels sprouts and broccoli will be a poor source.

And there is a cruciferous side effect…

boy wearing gas maskNo, it’s not a “thyroid killer” in healthy people, as some blogs have suggested. But there is one unpleasant adverse reaction which is quite  common, no matter how healthy you are.

It’s gas and bloating.

The reason this type of veggies – especially broccoli and Brussels sprouts – are famous for causing farts is because of a complex sugar they contain called raffinose.

Humans lack the enzyme a-galactosidase (a-GAL) which is needed to breakdown raffinose and other oligosaccharides. As a result, we have to digest these by allowing them to sit and ferment in the intestines with gas-producing bacteria.

The solution to this problem is straightforward, but it will require a supplement. Get some Beano on Amazon and chew a couple right before your next serving of broccoli. It works wonders with gas and bloating related to not just beans, but also the other sources of oligosaccharides like cruciferous.

Perhaps with those, you will feel even more comfortable eating them raw and uncooked and therefore, will get more of the glucosinolates. Now the idea of a raw broccoli salad isn’t to everyone’s liking, but just about everyone likes these raw broccoli poppers as a snack.
These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.