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Is There a Dark Side to Kale?

Kale, if you haven’t noticed, has topped the list as one of America’s TOP health foods. Once a pretty garnish on the salad bar, it is now commonly found in supermarkets, farmer’s markets, health stores and restaurants. Raw, blended, roasted, stewed or sautéed, kale has made a huge claim in the veggie department and has some promising potential for protecting against cancer, among other health benefits.

Some have claimed it to be “the age of kale”. Even the President dined on kale salad at his Thanksgiving feast as noted in The Washington Post. With this craze, people are learning how to amp up their kale intake by throwing massive amounts of kale, typically raw kale, into a blender with some other fruits and veggies and voila! they have breakfast. For most people, this is a very good thing! Getting more veggies into the diet can be a daunting task for some and green smoothies are an easy way to do it.

But is there trouble is this cruciferous paradise? Can too much of a good thing actually be not so good?

Like all things in the nutrition world the answer to this is, it depends.

Normal, reasonable (even daily) amounts of raw kale or other crucifers should not be a problem for most people. A normal person (without thyroid issues) who eats several servings of crucifers per day should not be at any risk, especially if these greens are cooked (but more on that in a minute). This has been confirmed by professors of nutrition at the Harvard School of Public Health. Consuming large quantities of raw cruciferous vegetables (often the foundation of a green smoothie) can have a dark side, however. Green smoothies are an easy, and relatively new way of guzzling down huge quantities of greens like kale and may come with some unwanted side effects if consumed in excess.

“It’s the dose that makes the poison” ~Dr. Teresa Fung, Harvard School of Public Health

Kale has a component called goitrogens, a substance that can contribute to enlarging your thyroid and limiting the function of your thyroid gland– in turn, lowering your metabolism. Sometimes it can contribute to the development of a goiter as well. For a population with ever increasing thyroid issues (especially women), this is not such a good thing. Cold hands and feet, intolerance to cold, hair loss, fatigue and decreased resistance to stress are all symptoms of thyroid problems and a slower than normal metabolism. If you are someone who knows they have a thyroid issue, or thinks they might be prone to one, it might be important to watch your goitrogen intake via sources like raw cruciferous vegetables (i.e. kale, collards, broccoli, etc.).

Do not despair! There is still some good news. 

Certain nutrients and cooking methods can limit the goitrogenic effect of raw crucifers, such as kale. Read on for some tips:

  1. Iodine: For those of us that are health conscious (and even those who are not), there may come a natural avoidance of table salt which, under public policy, is fortified with iodine. Since goitrogens inhibit iodine intake and its action, it’s important to get enough. If you don’t use iodized table salt on a regular basis, you might consider using a multivitamin that contains some iodine or eating more foods that are rich in iodine like seaweed, kelp, fish, eggs and some dairy products. And, a special caution to pregnant and nursing mothers: iodine is absolutely CRITICAL to the growth of your fetus, so it’s important to keep it in your diet regardless.
  2. Eat seaweed: Kale on it’s own is not going to give you a thyroid issue, but it could push you over the edge into a poor metabolic rate. As mentioned in #1, seaweed is a fantastic source of iodine and it can help you get what you need without resorting to the use of iodized salt. You can find seaweed at Asian food markets and selected grocery stores.
  3. Eat some raw, but cook it too!: Goitrogens are greatly diminished by cooking, so it’s good advice to boil, roast or stew your kale before eating. This is the same for any other cruciferous veggie like broccoli, Brussels sprouts, cabbage, cauliflower, collards, kohlrabi, bok choy, etc.).
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  4. Eat your kale with fat: Eating your veggies with fat increases the availability of fat-soluble vitamins D, E, A and K from the food source– a benefit you do not want to miss out on! Lightly sautéing or drizzling your crucifers with coconut oil, ghee, butter or extra-virgin olive oil are all nourishing ways to accomplish this task.
  5. Keep your green smoothie: If you have been drinking 1-2 green smoothies/day with kale or other crucifers, you are probably fine! It’s when you start replacing more than 2 meals each day with raw green smoothies that you might get yourself in trouble.

Remember, these recommendations are part of a comprehensive approach to total health. There is no magical food, no curative pill or perfect diet that will create perfect health. Drinking enough water, eating enough fiber, eating a variety of good fats and proteins, getting adequate sleep and exercising appropriately are other factors that will contribute to the lack or luster in your life.

TAKE HOME POINT: Daily raw kale, cabbage or broccoli is not going to ruin your metabolism or be a cause of major concern. It’s the dose that matters (as with many things in life), so it’s important to switch things up and do a little bit of everything. If you have a thyroid condition, it’s important to talk to your health care provider about whether or not cruciferous vegetables should be avoided or limited.

When I think about anything in life, typically the old adage comes to mind, “all things in moderation”. We often get hyped up about specific nutrients and foods in the nutrition realm, but the key is moderation. Getting a large variety of vegetables, in this case, is much better for you than trying to focus on one nutrient or food– kale in this case.

Do you have more questions? Schedule your appointment with me today and we can personalize your nutrition and optimize your health together!

In Health and Vitality,


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