Should you be adding spinach to your smoothie?
One of the questions I often get asked is whether raw spinach or kale in smoothies will impact thyroid function? There is a strong view that people with thyroid conditions should avoid goitrogenic foods as goitrogens can affect thyroid function. Whilst this can be true, it really is important to understand that not all goitrogens are created equal.
What are Goitrogens?
Goitrogens are substances that are released from certain plant-based foods when they are sliced or chewed raw. These plant-based foods are really important foods that are essential for supporting the liver to detoxify. Detoxification is very often an area where most people with Hashimoto’s or hypothyroidism need a little extra support, so limiting these food could potentially have a negative knock-on effect.
Goitrogens can be divided into three categories:
Good examples of these vegetables include spinach, kale, broccoli, cauliflower, brussels sprouts, all which help the liver to clear toxins from the body and support oestrogen metabolism (a big one for us girls). Cruciferous vegetables are by far the most goitrogen-rich foods, however several fruits, nuts, and grains also contain these compounds. What’s important to consider is that some have less of an effect than others and that not all goitrogens are created equal!
So what is the connection between goitrogenic food and thyroid health?
Let me first try and explain the science and then rewind the clock to the last century, so you can understand the reasons behind the fear of consuming goitrogenic foods.
Firstly, it is important to understand that goitrogen-containing foods can interfere with thyroid function by preventing iodine from being integrated into the thyroid hormones thyroxine (T4) and triiodothyronine (T3).
When thyroid hormone production levels reduce, the thyroid gland enlarges to compensate for this. This enlargement is known as a goitre. A goitre is usually a key indicator that someone is iodine deficient. Iodine is an essential nutrient for the thyroid, but deficiency can also have significant health consequences and potentially lead to brain damage, infertility and childhood mortality, to name a few.
Now that you understand how low levels of iodine (which can be exacerbated by the consumption of goitrogenic foods) can impact the thyroid, let’s rewind the clock to see where all the fear for these foods first started.
One of the leading causes of thyroid disease in the past was iodine deficiency. This was a global problem that set off the fear against the consumption of cruciferous vegetables. The truth is that iodine deficiency is no longer a global problem and whilst it still does exist and some individuals do end up with thyroid disease as the result of iodine deficiency, it is definitely a lot less common today.
To the contrary, in many cases iodine excess has become a bigger cause for concern. Excess iodine is a big risk factor for developing Hashimoto’s disease. When we consider that 90% of people with thyroid disease have Hashimoto’s, it’s important to understand that a large majority of people with thyroid disease may be sensitive to too much iodine rather than being deficient!
Testing for iodine
Whilst it can really help to understand whether you have sufficient or insufficient iodine levels, the most accurate way to test for this is to do an iodine loading test. I only recommend this test to individuals who do NOT have Hashimoto’s disease as it can potentially fuel the autoimmune disease process.
To eat or not to eat Goitrogens?
Individuals dealing with hypothyroidism as a result of iodine deficiency are the group of individuals who need to pay closest attention to goitrogenic foods. The good news is that these foods are only problematic when eaten raw, which means that you can include these foods providing they are slightly steamed, cooked or fermented. When you cook, steam or ferment these foods, you break down the compounds in goitrogens that block iodine, which means it won’t impact thyroid function.
If you are dealing with Hashimoto’s, I generally recommend that you pay close attention to how you feel when you eat raw goitrogenic foods. I think many people with Hashimoto’s can tolerate raw goitrogenic foods, but the question comes to how often and how much?
The thyroid is a great barometer and will generally tell you whether you can tolerate lots of spinach in your smoothies or not. My suggestion is to pay close attention to how you feel after enjoying these foods raw.
- Does it make you feel more tired
- Do you get pain around the thyroid
- Does it impact your gut function and lead to constipation?
- How does it impact your lab numbers?
I also advocate that you keep a close eye on your thyroid lab numbers to see whether you can pick up any changes from eating higher levels of raw goitrogenic foods, especially over the summer months.
Personally, I have a threshold and do limit high levels of raw goitrogenic foods as I have personally found that it gives me pain around my thyroid, impacts my energy and this also translates across my lab numbers.
Soy – the ONE to exclude!
There is one exception when it comes to goitrogenic foods that MUST be excluded and this is soy. The isoflavones genistein, daidzein and glycitein in soy reduce thyroid output by blocking activity of the TPO enzyme. For this reason, whether cooked or raw, you really shouldn’t include this food in your diet at any point if you are dealing with either hypothyroidism or Hashimoto’s.
Be your own detective and see what works best for you! Remember, we are all unique.