Cruciferous vegetables are some of the healthiest foods on the planet, and some of my personal favorites to eat. When I was diagnosed with Hashimotos, I found out there was a lot of confusion on whether or not those with thyroid problems should continue eating them.
Some sources claim cruciferous veggies should be avoided, especially raw, while others say they are fine to eat but recommend taking a natural iodine supplement to support the thyroid when eating cruciferous veggies.
I needed an answer to this question for myself.
When my doctor recommended eating broccoli sprouts, I asked his opinion on cruciferous vegetables. His answer and my research made me comfortable consuming these vegetables regularly… here’s why:
Glucosinolates and Goitrogens, oh my?
Cruciferous vegetables contain glucosinolates; which are metabolized into isothiocyanates (ITC) in the body. Research shows that these compounds are protective against various types of cancer. (1) Cruciferous veggies are also an excellent source of vitamins, minerals and phytochemicals that support the body in various ways.
At the same time, these veggies contain goitrogens, which can inhibit the body’s uptake of iodine. Research in animals showed that this blocking of iodine uptake may contribute to the development of a goiter, which is the reason that cruciferous veggies are often not recommended for those with thyroid disease.
So what is a person with thyroid disease to do?
In my opinion? Eat the greens.
Iodine, Selenium and Animal Studies
Dr. Joel Fuhrman explains:
Animal studies suggested the hypothetical thyroid issue from eating very large amounts of cruciferous vegetables years ago. However, no human study has demonstrated a deficiency in thyroid function from consuming cruciferous vegetables. Only one such study seems to have been conducted as of yet; in that study, no effects on thyroid function were observed in subjects eating 150 grams of cooked Brussels sprouts daily for 4 weeks. Raw cruciferous vegetables have not been investigated, however the only case report relating cruciferous vegetables to thyroid harm suggests that it would be almost impossible to consume enough cruciferous to harm the thyroid. This case was that of an 88-year old woman who developed hypothyroidism after eating 1-1.5 kg (2.2-3.3 pounds) of raw bok choy every day for several months; an excessive and unreasonable intake of raw cruciferous. In other words, a person would have to consume an insane amount of raw cruciferous to have a negative effect on thyroid function.
In fact, the opposite is actually true.
In today’s world, it is easy to have too much iodine, which as I explained before can be just as detrimental to the thyroid (and was for me). This is especially problematic if there is a deficiency in selenium as well. (2)
My doctor explained that if a person’s thyroid disorder is not caused by iodine deficiency, the iodine blocking properties of cruciferous vegetables are nothing to worry about (especially if the person is eating a nutrient dense diet that contains natural sources of iodine and selenium). He estimates that over 90% of thyroid patients have autoimmune thyroid disease and not simply low thyroid function because of iodine deficiency so cruciferous vegetables are almost always a non-issue.
In fact, too much iodine can actually be a factor in increased risk of autoimmune disease. In countries where iodine was added to the food supply to combat thyroid disease, rates of autoimmune thyroid disease increased. (3)
An excess of iodine, especially in supplemental form, can increase autoimmune attack on the body by inhibiting the ability of an enzyme called thyroid peroxidase (TPO). In these cases, the mild iodine inhibition from cruciferous vegetables can actually be helpful for those with thyroid problems.
Additionally, cruciferous vegetables may help the body produce glutathione, an antioxidant that is important for thyroid health and for mitigating autoimmune disease. Broccoli and broccoli sprouts contain sulforaphane, a cancer-fighting compound that has been extensively studied for its anti-cancer properties.(4)
Cruciferous vegetables are healthy and provide a variety of benefits, even (and especially) for those with thyroid disease. Of course, anyone with thyroid disease or any other health problem should work with a qualified doctor or functional medicine practitioner to find the best diet, medication, and lifestyle answers, but the existing medical evidence does not suggest that avoiding cruciferous vegetables is helpful.
In fact, cruciferous vegetables may be especially helpful for those with autoimmune thyroid disease because of their iodine-mitigating action. Consuming 2-3 pounds per day of raw green veggies would probably not be advisable, but then again, consuming 2-3 pounds of any single food group daily isn’t the best idea. If you’re concerned or think you might have non-autoimmune low-thyroid, just cook the veggies as this is shown to deactivate most of the goitrogens.
Personally, I eat a lot of green vegetables daily and consume about 75% of them cooked and only 25% raw. I also make sure that my diet contains natural sources of selenium and don’t supplement with iodine.
“Eat food, not too much, mostly plants.” -Michael Pollan