Written by Christa Orecchio, C.N
As a nutritionist, I often get asked if cruciferous vegetables can cause or worsen thyroid issues. As is the answer to most controversial and confusing nutrition topics, it depends on a myriad of factors such as your current state of thyroid, digestive, and brain health, how much energy you are able to produce (mitochondrial production), the quality of the vegetable (soil it was grown in and whether pesticides were used), your cooking method, and how often you consume these foods.
Cruciferous vegetables are vegetables that belong to the Brassica family. Examples include:
- Bok Choy
- Broccoli Rabe
- Brussels Sprouts
- Cabbage (all kinds)
- Collard Greens
- Radish (includes Daikon)
Being high in powerful antioxidants like sulforaphane and vitamin C, fiber, carotenoids, vitamin E and K, and folate, there is quite a case for consumption of these foods as a big contribution to enjoying greater health.
They have long since been touted as supportive medicinal foods that help prevent cancer, support the liver, and contribute to improved immune and neurological health.
However, cruciferous vegetables offer a unique dichotomy because they also contain compounds called glucosinolates which are connected to exacerbating iodine-deficiency related hypothyroidism that can lead to thyroid swelling called a goiter. Hence these foods are referred to as goitrogenic foods.
They can do this by blocking the body’s ability to uptake iodine, which every cell of the body needs, but especially the thyroid, which contains the highest concentration of iodine in the human body. Those with pre-existing hypothyroidism may find that excessiveconsumption of raw cruciferous vegetables, could further suppress thyroid activity.
However, you may have heard the saying “the dose makes the poison” and it takes a lot of brassica to be clinically significant.
Many clinicians believe that one would have to eat a ton of raw cruciferous vegetables, in excess of 1-2 pounds daily to have an adverse effect on the thyroid.
You can start off with a smaller amount and work up from there. According to a study in Human Toxicology, no effect on thyroid function was observed in people who ate almost 1 cup of cooked Brussels sprouts daily for 4 weeks.
How Cooking and Fermentation Help:
Steaming your veggies until they are fully cooked reduces the goitrogens to one-third of the original content while boiling for thirty minutes is known to be a reliable way to destroy 90% of the goitrogens (which are released into the water and discarded).
Cooking also reduces other goitrogenic compounds in foods called nitriles.
Fermentation is another way to make them healthier for you. When you ferment something like cabbage, it actually increases the goitrogen content but truly reduces the nitriles by 50% or more, making the benefits of fermented vegetables far outweigh the goitrogenic risk to the thyroid that raw cabbage could potentially propose in large amounts.
What About Green Smoothies?
If you are worried about goitrogens or have been diagnosed with hypothyroidism, then add steamed greens (instead of raw) like kale and Collards to your morning green smoothie or only add raw kale to your green juice once or twice a week versus daily.
You may have seen the recent article in Mother Jones entitled “Sorry Foodies: We’re About to Ruin Kale” where they discussed how kale can uptake thallium, a toxic heavy metal from the soil. They also included other cruciferous vegetables in the article like cabbage, watercress, radishes, and turnips.
Again, there are many factors involved here and this doesn’t mean that you should not eat these foods. The quality of the soil is the key. The majority of organic farms (which test their soil) likely do not have dangerous levels of thallium. Because thallium contamination comes from nearby oil drilling, cement plants, and coal burning, it’s good to find out if the farm you purchase your kale from has exposure to these things. Or better yet, grow your own organic veggies in clean, nutrient rich soil.
The Bottom Line
It’s worth repeating not to go overboard with any one food so don’t eat a diet of just kale or any other vegetable for that matter.
If you are concerned about this and have hypothyroidism, then steam or boil your cruciferous vegetables and limit them to 1.5 – 2 cups/day.
This way you can still benefit from their high micronutrient profile and their anticancer benefits while supporting your immune function and brain health. These health benefits will support cellular energy and mitochondrial health, which is highly supportive to the thyroid gland.
I often operate by the mantra, “don’t guess at it, test it” so be sure to ask your doctor about testing your iodine levels and get adequate iodine from your diet.
Getting Iodine From Your Diet
Being in the nutrition field I am not a fan of iodized salt because it contains 2.5% chemicals in the form of anticaking agents and is exposed to extremely high heat during processing. This process removes much of the minerals, which in turn can create a mineral deficiency and therefore more salt cravings (because a craving for salt is a craving for minerals) as the body intelligently seeks to fill in its nutritional gaps.
Source – FoodBabe