One of THE MOST commonly asked questions I receive is can I eat cruciferous vegetables if I have hypothyroid disease?
Cruciferous veggies, otherwise known as the brassica family of vegetables, include kale, broccoli, cabbage, cauliflower, bok choy, turnip tops, and brussel sprouts. I don’t know about you, but these are some of my all-time favorite vegetables to cook with! Plus, the cruciferous vegetables are well known for their health benefits which include being a high source of fiber and also may be effective at fighting cancer. These veggies contain a substance known as Indole 3 Carbonyl (13C) that targets multiple aspects of cancer cell cycle regulation and helps to benefit estrogen metabolism.
Although this all sounds great, lately these veggies have been getting a really bad rep for harming the thyroid!
The claim is that the cruciferous vegetables contain certain substances known as goitrogens (goiter producing substances) that could cause the thyroid to enlarge or slow down, and reduce the absorption of iodine (important for thyroid function). These vegetables also contain a substance known as thiocyanate, which may interfere with iodine absorption to further damage the thyroid. Obviously for all of us that have hypothyroid, this reads as a huge red flag causing many of us to consider removing these delicious vegetables from out diet.
However, there are very few studies that suggest that these claims are true. In fact, some studies show that the risk may be minimal at best.
Fact #1: Researchers at the University of California found that only certain types of cruciferous vegetables may actually reduce the amount of iodine uptake. These were: collard greens, brussel sprouts and Russian kale. But other cruciferous vegetables such as broccoli, kale, turnip tops and broccoli rabe contained less than 10umol of goitrogenic chemicals per 100g servings and researchers concluded that these veggies therefore posed minimal risk to the thyroid.
Fact #2: In another study, researchers provided participants with 150g of brussel sprouts every day for 4 weeks. Remember, these Brussels are supposed to interfere with iodine uptake. The brussel sprouts used in the study did in fact contain a high amount of chemicals thought to harm the thyroid. However, the chemicals did not affect the thyroid function of the participants. Measurements of thyroid hormones were unchanged after the 4 weeks!
Fact #3: Other studies have shown that cooking these “goitrogenic” foods, especially lightly steaming them, can inactivate the goitrogens! It appears that the sweet spot for de-activation of these substances is steaming for 3-4 minutes.
Bottom line: Cruciferous vegetables, including kale, broccoli and cabbage have many health benefits and do NOT seem to be as problematic to the thyroid as some are claiming. That said, if you have hypothyroidism, it would be recommended to cook or lightly steam or crucifers more often to ensure you are not being exposed to high levels of goitrogens. Additionally, if you love raw crucifers and often eat them uncooked, it would be a good idea to have your thyroid hormone levels checked via blood work to ensure that these vegetables are not interfering with your medication or affecting your thyroid health in any way.
I know changing your diet and lifestyle for the better can be difficult to say the least. This is why I created the Thyroid Truths Grocery List- my top non-negotiable food items when eating to improve thyroid health. It's also perfect to print and keep on the fridge! Download it here :)
Do you love cruciferous vegetables as much as I do? What’s your favorite way to cook them? I will be sharing my favorite cauliflower recipe with you all soon- so stayed tuned. In the meantime, I would love to hear from you! Leave your comments below!
Dr. Emily
Paxman PJ and Hill R. The goitrogenicity of kale and its relation to thiocyanate content. J Sci Food Agric. 1974;25(3):329-337.
Nutr Rev. 2016 Apr;74(4):248-58. doi: 10.1093/nutrit/nuv110. Epub 2016 Mar 5.
Hum Toxicol. 1986 Jan;5(1):15-9