We all know green smoothies are a wonderful way to get extra nutrients from vegetable sources throughout the day. I mean, duh, that's why you're drinking them. But, it is important that you slightly cook the greens (at least the cruciferous ones) before you freeze them in your homemade smoothie packs for on-the-go deliciousness. And here is why:
The goitrogen debate
Cruciferous vegetables (such as kale, spinach, broccoli, Brussels sprouts, cabbage, cauliflower, collard greens, radishes, turnips, kohlrabi, bok choy, and cassava) are called "goitrogenic", because of naturally occurring substances that can cause growth of the thyroid gland. These goitrogens also act like anti-thyroid chemicals, inhibiting iodine metabolism, slowing down the function of the thyroid, which can lead to hypothyroidism, or under-active thyroid.
Symptoms of a under active thyroid include feeling weak/tired, inability to tolerate cold temperatures,
cold/dry skin, thinning/brittle hair and nails, yellowish tint to skin, or slow body movements.
Using these cruciferous vegetables in smoothies or juices, only when not cooked, means you are ingesting a concentrated dose of these goitrogens. Now, this may not be an issue for most healthy individuals, and, in fact, if you have an over active thyroid, this may be a great natural therapeutic approach for your condition to discuss with your clinical nutritionist. But, if you are worried that you may have an under active thyroid, you may want to proceed with a bit of caution.
Low carbohydrate diets and the thyroid
This is especially important to consider when on a low carbohydrate diet. It can take some time while eating a paleo diet to find the amount of carbohydrate consumption that is right for you (and this amount will probably change over time). If you are eating too little healthy carbohydrates while you are trying to adjust, your body's thyroid may already be a little under active. So, if you are consuming these uncooked cruciferous vegetables often, it may be making the problem slightly worse (especially for females).
You can read more about healthy sources of carbohydrates for a paleo diet by clicking this link.
NOM ALL THE CRUCIFEROUS VEGGIES...
Let me make myself very clear: I am NOT saying that these vegetables aren't obviously ridiculously healthy, nutrient-dense super foods... Because they are! And I am NOT stating that you should limit these foods in your diet in any way. In fact, I am stating the opposite: Eat all the healthy cruciferous veggies you can!
Correct consumption of these foods, which contain many essential micronutrients for thyroid health (such as zinc, copper, and iron), has actually been shown to support proper thyroid function. In fact, these vegetables also contain many antioxidant compounds that help your body protect against cancer - even thyroid cancer!
What I am saying, is that cooking these foods, such as steaming or boiling, can inactivate some of the goitrogens and make green smoothies safer for those at a greater health risk - especially when consuming these foods frequently.
Steaming these vegetables also helps the digestive system by making the nutrients from these foods much easier to absorb and significantly increases the bile acid binding potential of these foods, which lowers the risk of cardiovascular disease. A way to make green smoothies even healthier? Yes, please! Now, whip out that blender and get to work!
An up-to-date look at goitrogenic substances in food.
Females, carbohydrates, and hormones.
All about goitrogens.
APPRAISAL OF THE GOITROGENS: RESULTS OF TREATMENT WITH THIOURACIL, PROPYLTHIOURACIL AND RELATED ANTITHYROID DRUGS