Ahh kale, everyone’s favorite green, nutrient-dense veggie.
When I trained as a health coach back in 2011, we all got a little obsessed with kale. Regular kale. Curly kale. And my very favorite, Cavolo Nero.
I started eating kale a lot – almost daily! Including raw in my morning breakfast green smoothie. Then I had a wakeup call to an important life lesson (again):
Moderation and variety are important in all things – even healthy foods!
A trip to the doctor (because of unusual tiredness, poor digestion, and low appetite) revealed that my thyroid was very underactive.
And then some internet research turned up a possible cause – some foods are goitrogenic, meaning that they suppress thyroid function. And what did I find on that list of foods, but my beloved kale!
Could it be true? Could eating too much kale be the cause of my low thyroid?
Maybe you’ve seen those pictures from old medical books of people with huge Goiters on their throat (they made an impression on me when I was a kid!) As I understand it, a goiter is an extreme swelling of the thyroid. Similarly, goitrogenic foods suppress the action of the thyroid, which can cause goiters in extreme cases, or less severly, can contribute to low thyroid (hypothyroid).
Common goitrogenic foods include: cabbage, collard greens, bok choi, KALE, cauliflower, broccoli and brussels sprouts.
Yep, loads of very healthy foods on that list.
Should you stop eating cruciferous veggies?
No! Cruciferous veggies (like the ones listed above) are super healthy and packed with good nutrients.
My problem (I think) is that I was eating way too much kale – no variety, no moderation. I was also eating a lot of it raw in green smoothies (some sources indicate that eating these veggies cooked deactivates the thyroid-suppressing effect.)
So how much kale was I eating?
A lot. Too much. I went from never tasting kale in my life, to eating it almost daily – sometimes twice per day.
Was too much kale the cause of my low thyroid?
I don’t know.
But when I think about what changed between the previous year (normal thyroid reading) and that year (low thyroid reading), the two major differences are: 1) higher stress levels and 2) lots of kale!
But I am so happy to report that after 5 months of healthy eating, de-stressing and cutting back on kale has my thyroid almost completely back to normal (woohoo!).
So what does this mean for you? How do you know if you’re eating “too much” kale? Should you eat it at all? Are there other foods that can suppress your thyroid function too? In the past 5 months, I’ve done a ton of research about the kale-thyroid connection, and there’s a lot to learn. Let’s dig in.
Why does kale suppress thyroid function?
Stick with me through 30 seconds of science talk, and then we’ll get back to the practical information.
Kale is a cruciferous vegetable (also known as brassicas). Cruciferous veggies include cabbage, kale, broccoli, cauliflower, bok choi, arugula (rocket), turnips and watercress (get a longer list of cruciferous vegetables here). There are a lot of healthy veggies in the list!
The connection with the thyroid is that in addition to their healthy compounds, cruciferous vegetables also include isothyocyanates which can inhibit the uptake of iodine by your thyroid – which decreases the amount of thyroid hormone produced and results in ‘underactive thyroid’ or hypothyroidism. (Check out this link for more techincal information on how cruciferous vegetables affect thyroid)
Rather than remembering all of this, it’s probably easier to remember that cruciferous veggies like kale contain contain goitrogens. (From Wikipedia: “Goitrogens are substances that suppress the function of the thyroid gland by interfering with iodine uptake, which can, as a result, cause an enlargement of the thyroid, i.e., a goiter.)
And it looks like goitrogens can suppress thyroid function in susceptible individuals (who are predisposed to low thyroid, or have low iodine intake, etc.)
Apparently, I was susceptible!
Can I ever eat kale again?
YES! Yes, yes yes. Please do eat kale. It’s tasty and packed with nutrients!
You probably just don’t want to eat it raw in smoothies, every day, for a long period of time.
Mix up your greens! Try different greens from different families (for example, add in some romaine lettuce to your green smoothies). And if you’re eating cruciferous veggies, try cooking them first, at least some of the time. If you are a green smoothie drinker, here are some guidelines for rotating your greens.
What’s a ‘normal’ amount of kale to eat?
If you’re a bit of a greens addict, like me, it can be hard to remember what a ‘normal’ serving is.
This study from 1986 showed that people who ate 5 ounces (2/3 cups) of cooked Brussels Sprouts daily for 4 weeks, had no adverse impact on thyroid. Of course, that’s cooked brussels sprouts, where the goitrogens are mostly deactivated.
I couldn’t find any research or firm guidelines on what is safe to eat for thyroid function. So I think this is where you use common sense and listen to your body. If you have any thyroid issues or a family history of them, really limit your intake of raw cruciferous veggies and instead, eat them cooked.
Personally, at this point, I’m only eating raw cruciferous veggies as a small amount of homemade sauerkraut. Other than that, it’s all cooked.
But that’s just me. I’d love to hear what you’re doing if you’ve also cut back on kale and cruciferous veg – let’s discuss in the comments!
What other foods can suppress thyroid function?
It’s not just kale. It’s all of the cruciferous veggies I mentioned above, and a few other sneaky additions:
- Soybeans (this is one of the hardest to avoid because many processed foods include soy!)
- Pine Nuts
- Sweet Potatoes
There are also a few lesser-known cruciferous vegetables:
- maca (are you putting this in your smoothies too?)
- canola / rapeseed
- arugula (rocket)
Again, it doesn’t mean to not eat these foods – just to be aware of them if you’re dealing with a low thyroid issue.
And it’s not just foods – what about chemical exposure?
Not surprisingly, thyroid function (like most other things in our bodies) is affected by environmental toxins as well. Even more reason to DIY your beauty products!
- Bromine – in processed baked goods, some hard plastics, citrus flavored sodas etc.
- Flouride – in toothpastes, urban drinking water
- Triclosan – in antibacterial hand wash and soaps
This is an area I’m just starting to look into – stay tuned for more information on this and healthy DIY alternatives to these products!
Where can I find more information?
Here are some of my favorite resources for learning more about the kale-thyroid connection (and how to nourish your thyroid back to health – naturally!)
- Listen to this awesome podcast about thyroid health with health coaches Sarah Wilson and Andrea Beaman.
- Read Aviva Romm’s book: The Adrenal Thyroid Revolution
- The super-comprehensive About.com thyroid site – highly recommended.
- Traditional methods of eating cruciferous veg and a deep look into the dark side of these vegetables. Weston A Price Foundation.