Dispelling nutrition myths, ranting, and occasionally, raving

Is your “green monster” a nutritional nightmare?



I recently came across a blog post decreeing green smoothies to be a nutritional no-no. Great, so people finally find a way that works for them to get a bunch of veg and fruit in one go and now we tell them that these drinks might be the death of them.

Green smoothies seem like a no-brainer. If you’re making them at home you can easily control what goes into them and ensure that they’re packed with nutritious foods and not calories from things like frozen yoghurt. I know a lot of people who find it difficult to eat breakfast in the morning; smoothies can be a great way to get breakfast in as liquids may be more readily tolerated than solid foods first thing in the morning.

Now that people are hooked on green smoothies the fearmongering begins. Why should you fear your green smoothie? Well, raw cruciferous vegetables, such as kale, a staple in many green smoothies, contain goitrogens. These are substances that interfere with thyroid gland metabolism by inhibiting the absorption of iodide. When consumed in large quantities, they may cause goiters. Goitrogens are also found in turnips, cabbage, brussels sprouts, cauliflower, broccoli, and water.

Iodide (not to be confused with the toxic iodine, despite “iodine” being used interchangeably with iodide) deficiency hasn’t been a significant health concern in developed countries in many years because we generally cook cruciferous vegetables before eating them. In Canada, fortification of table salt with iodide is also mandatory. However, with the diminished use of the salt shaker and the popularization of sea salt (which is not fortified and loses iodide during processing) it’s likely that iodide will become a nutrient of greater concern in countries such as Canada.

Before you start reaching for the iodide supplements (which, by the way, you’ll find as kelp or bladderwrack, not as iodide/iodine) you should be aware that at very high amounts (more than 1.1 mg per day), iodide consumption can inhibit thyroid hormone synthesis. Even without consuming fortified table salt, most North Americans consume more than enough iodide per day as iodide is used as a sterilizing agent in dairies and restaurants, a conditioner for dough in bakeries, and in food colourings. Iodide is also found in saltwater fish (both fin and shell), molasses, seaweed, plain yoghurt, milk, and eggs. Some protein bars and multivitamins also contain iodide.

Back to your green smoothie. Should you be concerned about the effect your daily smoothie might have on your thyroid gland? Probably not. Unless you’re guzzling green smoothies for breakfast lunch and dinner, are consuming a cruciferious vegetable-heavy raw-diet, and have an existing thyroid condition it’s unlikely that a green smoothie once a day, or less, is going to have anything but a positive impact on your health. The most important feature of a healthy diet is variety. Consuming too much of anything be it green smoothies, potato chips, bread, or bananas, is unhealthy. Eating a balanced diet containing a variety of foods helps to ensure that you’re getting all of the nutrients you need. And yes, a green smoothies can be a part of a balanced diet.

Author: Diana

I'm a registered dietitian from Nova Scotia, living and working in Ontario, Canada. My goal is to help people see food and nutrition from a different perspective and understand that nutrition and health are not necessarily a result of personal choice.

6 thoughts on “Is your “green monster” a nutritional nightmare?

  1. Thank you Diana for providing a much-needed voice of reason on nutrition. When did we all become so fearful, neurotic (and for that matter; political) about our food?


  2. Sigh, I heard this one too, just another way to make food seem scary! No wonder people are confused, we have high rates of eating disorders and obesity… who knows what to eat! Do you know any good articles (and by good, I mean evidence based) about getting iodine from a vegan diet. I am an ethical vegan, and while I do use iodised salt sometimes, I would think not enough. A lot of the foods you mentioned we get our iodine from are not vegan. I also have Hashimotos, so I don’t want to take iodine supplement. Haha, food is confusing!


    • That certainly does make it more difficult! Obviously, I can’t provide you with specific nutrition advice here. If it’s possible, you should ask your doctor for a referral to a dietitian.

      As far as iodide-containing vegan food options go, anything grown in or near the ocean would be a source of iodide. Seaweeds and sea vegetables are good options. Soy protein is actually a source of iodide but also a source of goitrogens. However, those should be destroyed by cooking. Not knowing what medications you may be taking though, soy might not be an option for you. As mentioned in my post, flour may also be a source of iodide. We don’t need much iodide in our diets but you could might consider taking a vegan multivitamin if you’re not getting enough nutrients from your diet.


  3. Always such a balanced view on these things – thanks Diana!


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