The Dark Side of Green Smoothies
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The Dark Side of Green Smoothies

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The green smoothie fad has taken the world by storm, with everyone from staunch vegans to Paleo people hopping on the kale-and-spinach-laden beverage bandwagon. While green smoothies have gained a reputation for being extremely healthy, these drinks have a dark side that few people are aware of. Read on to learn about the health problems associated with the "over-enthusiastic" consumption of green smoothies and why drinking these beverages regularly may not be conducive to optimal health.

Are green smoothies healthy
Are green smoothies really as healthy as we think they are?istockphoto.com/Kkolosov

Green Smoothies: Not Necessarily a “Health Food”

In the health community, the green smoothie has become the poster child for healthy eating. If you are a green smoothie fan, your typical recipe probably looks something like this:

  • 1 apple, peeled, cored, and chopped
  • 8 ounces unsweetened almond milk
  • 2 cups stemmed and chopped spinach or kale
  • 1 cup broccoli

This green smoothie is full of veggies—spinach, kale, and broccoli—so it must be healthy, right? Well, not necessarily. While cruciferous vegetables and leafy greens certainly have health benefits, consuming large amounts of them in green smoothies may not be healthy in the long run, for several significant reasons.

  1. Cruciferous vegetables, such as kale, broccoli, cauliflower, and cabbage, have been found to contain high levels of a toxic heavy metal, thallium.
  2. Cruciferous vegetables contain goitrogens, which are naturally occurring plant chemicals that inhibit the uptake of iodine by the thyroid gland and reduce the production of thyroid hormone, thus lowering thyroid function.
  3. Many leafy greens, such as spinach and collard greens, are high in oxalates. Oxalates are plant-based compounds that may promote kidney stone formation and inflammation when consumed in large amounts.

As you can see, it may be time to reconsider whether regularly drinking green smoothies is a wise choice for our health.

Cruciferous veggies and leafy greens undoubtedly have many health benefits, but consuming large amounts of them in green smoothies may not be healthy in the long run

Are There Heavy Metals in Your Kale?

The soil in which vegetables grow has a significant impact on their micronutrient content. However, just as beneficial minerals are transferred from soil into plants, so too are toxic metals.

Unfortunately, research shows that the toxic heavy metal thallium, which occurs in soil as a byproduct of smelting and coal-burning, preferentially accumulates in cruciferous vegetables such as kale, broccoli, cauliflower, cabbage, brussels sprouts, and bok choy. (1) This means that people who eat a lot of cruciferous vegetables, as green smoothie aficionados are wont to do, may be exposing themselves to high levels of thallium. In fact, an astute molecular biologist and alternative health practitioner named Ernie Hubbard found this to be just the case among his health-conscious clients, who were experiencing many bizarre symptoms that did not fit any standard disease pattern. After much investigation, he was eventually able to trace their symptoms back to thallium toxicity resulting from their cruciferous vegetable-heavy green smoothie habits. (2)

Unfortunately, when it comes to thallium, even low-level exposures can cause symptoms such as nausea, diarrhea, stomach pain, hair loss, and peripheral neuropathy. (3) While some medical authorities have argued that toxic metals are present throughout our environment and that we shouldn’t worry about trace levels in otherwise-healthy vegetables, the problem remains that heavy metal exposures are additive and synergistic. Many heavy metals have similar adverse effects on the body, so continuous consumption of thallium in vegetables, plus daily exposure to other heavy metal sources, exponentially increases the body’s toxic burden. Based on this evidence, if you are regularly drinking green smoothies and experiencing any unusual health problems, it may be time to investigate your thallium level and reconsider your green smoothie habit.

If you aren’t ready to get rid of your green smoothie just yet, at least consider using only organic cruciferous vegetables in your drink. Soils that are rich in carbon-based matter, such as soil on organic farms, have been found to impede the transfer of thallium into plants; this effect is less likely to occur in the carbon-depleted soils used on conventional farms. This means that organic produce may contain lower levels of heavy metals, such as thallium, compared to conventionally raised produce, potentially resulting in a healthier green smoothie. (4, 5, 6)

Green Smoothies and the Thyroid Gland

Concerningly, green smoothies may also have adverse effects on the thyroid gland. The thyroid gland requires the mineral iodine to produce thyroid hormones. Cruciferous vegetables—common ingredients in green smoothies—contain compounds called glucosinolates, which inhibit iodine uptake by the thyroid. This may result in a reduced ability of the thyroid gland to produce hormones, leading to reduced function and, potentially, thyroid disorder. (7) Furthermore, the risk of high cruciferous vegetable intake impairing thyroid function is greater in people with iodine deficiency. Iodine deficiency is not uncommon in folks on a Paleo or otherwise “healthy” diet, since the main dietary sources of iodine available are sea vegetables, iodized salt, dairy, and fortified foods, which are often excluded on a Paleo or unprocessed diet.

While large quantities of raw cruciferous vegetables pose a problem to the thyroid gland, cooked cruciferous vegetables appear to be much safer. Cooking cruciferous vegetables stimulates the production of an enzyme called myrosinase that helps to deactivate goitrogenic glucosinolates. (8)

Opting to eat cruciferous vegetables in their whole-food form is another way to reap the health benefits of these vegetables without getting a heavy hit of goitrogens; it is much harder to overeat vegetables when they are in their whole form versus juiced or blended in a green smoothie.

Sometimes it’s the foods we least expect that may be contributing to our health issues. On their face, green smoothies seem like a great health food, but if you have a thyroid disorder, they may be causing you problems. Green smoothies aren’t the only food with potential hidden health concerns. Depending on your health and any underlying chronic illnesses that you have, various other health foods may be making you worse rather than better.

Where should you turn if you want to learn more about the interaction between our bodies and our nutrition? This site is a great place to start, and we will always work to bring you the latest evidence-based information about how diet affects people’s health.

What if you want to use that information to help other people choose the right foods for them? The ADAPT Health Coach Training Program not only provides you with an education in Functional and ancestral health, but it also helps you understand how various foods and nutrients play a role in our health and chronic illness. Students in the program learn about thyroid disorders, gut dysbiosis, HPA axis dysregulation, and other health concerns and how various diets affect these conditions. Find out more about the ADAPT Health Coach Training Program.

Oxalates in Green Smoothies

Another significant problem with green smoothies is that they are often high in oxalate, a type of naturally occurring plant compound that promotes kidney stone formation and inflammation in certain people when eaten in excess. (9) Oxalate occurs in high amounts in spinach, chard, dandelion greens, beets, collard greens, berries, broccoli, cabbage, and carrots. In some people, oxalates accumulate in body tissues and provoke inflammation. In fact, oxalate accumulation has been associated with chronic pain, nephrolithiasis (aka kidney stones), neurological symptoms, vulvar pain, and fibromyalgia pain.

Currently, a high oxalate intake is defined as the consumption of 250 mg oxalate per day. For reference, one cup of raw spinach contains around 656 mg oxalate. (10) As you can see, it would be quite easy to overdo it on oxalates if you are regularly drinking green smoothies, which often contain a cup or more of spinach! Research has confirmed that green juices made using common vegetables contain high levels of soluble oxalates and that the consumption of these drinks may precipitate oxalate kidney stone formation. (11, 12) Some green smoothie proponents advocate “rotating” greens to include low-oxalate options such as mustard greens, watercress, and lettuce; this may help prevent green smoothie-induced oxalate overload.

Certain genetic variants, such as the SLC26A1 variant, and pre-existing gut issues, such as Crohn’s disease and dysbiosis, may increase an individual’s susceptibility to the harmful effects of dietary oxalates. For these individuals, reducing dietary oxalate intake may significantly relieve symptoms. (13, 14)

Replenishing the gut with beneficial bacteria from probiotics and fermented foods may also assist in the degradation of oxalate, since several probiotic species, including Lactobacillus rhamnosus, Bifidobacterium animalis subsp. lactis BI07, and Oxalobacter formigenes, have been found to degrade dietary oxalate. (15, 16, 17)

Final Thoughts on Green Smoothies

Unfortunately, green smoothies are not quite as healthy as we have been led to believe, due to their thallium, goitrogen, and oxalate content. Rather than relying on green smoothies as a primary source of vegetables, I recommend eating veggies in their whole-food form and cooking cruciferous vegetables to lower their goitrogen content. If you are not ready to forgo green smoothies entirely, choose organic vegetables, which may be lower in heavy metals; rotate your greens so that you are regularly including low-oxalate options such as mustard greens and watercress; and consider supplementing with oxalate-degrading probiotics such as Lactobacilli and Bifidobacteria.

  1. Well, finally! I thought I was the only one in the US that finds these “smoothies” vile in taste and texture. Don’t get me wrong — I love green veggies and eat huge salads. I love spinach, and I love blueberries. But blending them together into a vile-tasting soup? No thanks! I also love a cup of good, strong coffee, and I’m a fan of a glass of an excellent Cabernet Sauvignon. The very thought of blending them together makes me gag. People will never learn to appreciate the bright, distinctive tastes and textures of healthful fruits and veggies if they make an amorphous mush of them. Throwing all your food in a blender and drinking it is just abhorrent. It’s what we do for infants when weaning them off breastfeeding. I’ve been able to eat regular, grown-up food for decades now..

    • You are right. Why mess up the nice tastes and textures of so many different foods by blending them all together into a… drink?! Baby food! What are our teeth for?

  2. I agree about oxalates in greens causing problems. But greens are not the only veg high in oxalates. I messed my body up by drinking 2 cups a day of carrot juice for 1 month. At the end of that month I had to set up an appointment with the rheumatologist. It started with a feeling of warmth in my extremeties which I thought was curious but not unpleasant. But withing a week or so it turned into awful pain in each and every one of my joints, and even soft tissue. Fast forward 2 years and I am still suffering. Extremely low oxalate diet eliminates all of the symptoms like I never had them but if I slip up, they flood right back within minutes. I always wondered if I am going to be sensitive for the rest of my life. Before my carrot juice “healing” regimen I could eat whatever I wanted. In retrospect very high oxalate foods did cause me some slight problems all my life but they were NOTHING compared to what came after I unwittingly sensitised myself.

    • If you’ll read my comment elsewhere here, there is a link to info on carrot juice (and its fermentation to remove oxalates).

      I have never, though, ever heard of anyone consuming a relatively small amount of carrot juice and having such a severe reaction as you did. I know of people who consume quarts of the stuff every day and have nothing but good results. Just saying.

    • I did a provoked urine toxic metals test. My functional medicine doc used Doctor’s Data, but I think there are other specialty labs that offer the urine toxic metals test as well.

  3. Well, I’ve been looking around for more info on this topic and this is what I have found: that fermentation of high-oxalate juices is the way to go if you want to avoid the anti-nutrients, but don’t want to cook your greens.

    http://www.dailyiron.net/fermentation-oxalic-acid/

    They mention both carrot juice as a source of iron as well as the usual greens that are unhealthful when consumed raw and unfermented.

  4. Not just green smoothies though… Paleo Gluten Free diet is invariably high oxalate. Possibly also a challenge for FUT2++ Non Secretors who can’t retain probiotics easily and are more prone to inflammation. New FB group if that is you… If you get the only accurate list from Trying Low Oxalates Yahoo or Facebook groups (and need to ask as there are copyright issues with the testing University) you can see that. It has changed my life and an essential part of getting rid of SIBO to reduce the high and very high oxalate foods.

  5. I got prostate stones from eating spinach every day for a couple of years. Excess oxalate consumption. I believe vegetables and fruits are to be eaten only in season. Before the advent of refrigeration and modern transportation methods this was the norm.

  6. The things mentioned in this article are important aspects of green smoothies to consider. But green smoothies aren’t all the same. Mine is: strawberries, arugula, romaine, parsley or cilantro, avocado, and green tea instead of water, and all organic. I love how this smoothie makes me feel, and elimination (as in BMs) are perfect when I have them every day. Maybe this article would be better titled as: Beware of Kale and Broccoli in Smoothies.

    • I agree! Check out my reply this article is extremely frustrating. As the average paleo type eater can easily eat one cup of broccoli and 2 cups leafy greens

  7. I wish the article was a bit more upbeat, positive. You can say the same thing in a more positive way. We are all seeking better health. I drink an organic Kale shake with nothing but lemon and stevia every day. No fruit but lemon. Since starting this I am MUCH healthier.

  8. Thanks for writing about the dangers of green smoothies. I developed an oxolate problem after drinking green smoothies. They were probably not entirely to blame as I was also eating a lot of nuts at the time. It took me quite a while to figure out what the problem was. I had never heard of oxalates before. My symptoms improved after slowly lowering my oxalate intake. But I still cannot eat even a tiny amount of spinach without getting symptoms.

    • Ann, could I ask what symptoms you experienced that you tied to oxalates? Did you have to do anything to resolve these symptoms other than not consuming high-oxalate foods?

      • My symptoms were excruciating neck & shoulder pain & profound fatigue. Since adopting a low oxalare way of eating I have my life back! Look up lowoxalatediet

      • The main symptoms I had were anal and vaginal irritation. Sometimes to the point of bleeding. I also got random rashes that there seemed to be no reason for. But there are a multitude of other symptoms people get because the crystals that form can lodge just about anywhere in your body. I pretty much just slowly lowered the oxalate content of my diet(although it is recommended to take magnesium or calcium citrate with meals) and the crystals gradually left. They felt like needles coming though my skin. The tryinglowoxalates group is probably the best source of information. They have the only reliable list of foods and oxalate content.

  9. Seems like the old adage; “do everything in moderation” wins again.

    What is it with Americans, that we’ve become the culture of; “If a little bit is good, then a huge, ginormous amount must be much better.” ? So weird.

  10. Hello, I drink almost every morning a smoothie which includes: 6 leaves of lettuce, a handful of parsley, a cucumber, a banana not too ripped, a bit of avocado and one TBS of grounded chia or flax seeds. I don’t feel too well but think at least I have the opportunity to eat many green veggies. This is not giving me a satiety feeling and I wonder if it is a good idea at all? Any thoughts? Better breakfast suggestions? Thanks Raquel

    • Oddly tests have shown that drinking smoothies do not fill us up as well as eating the ingredients. After much testing they found that eating a smoothly with a spoon made you more full. It is the speed with which a person drinks their smoothies that causes the problem.

  11. In my green smoothie I also, besides the greens, include cauliflower, okra, butternut squash, artichoke hearts, 1 lemon, knob of ginger and water. I make enough for four days and drink about 12 oz. at a time. I have been doing this for a couple of years and I have not had any adverse side effects. So, I am assuming this is a good addition to my diet. (?) when I drink it, it always gives me a spurt of energy and a sense of well being.

  12. Green smoothies can also be just romaine lettuce, herbs, oil such as almond (mine is fresh pressed at home), olive, or hemp and a little pure water, sea salt.

    There are all kinds of green smoothies.

  13. I have a green smoothie every other day. I have kidney stones and I know why. I did a superfood diet for 6 months that caused it. To many oxilates. Now I stop all fad diets. I also try to drink more water. I hope every other day is okay. Thanks for the article.

    • Cathy, if you still have stones, why are you still drinking these shakes? Stop. You’re keeping your “tank” topped off by every other day drinks…you never let your body rid itself of these toxins…

  14. The thallium-kale story:
    http://craftsmanship.net/the-vegetable-detective/
    Thallium is a lot like lead. Organic may not be the answer either, as in paragraph beginning “The more Hubbard nosed around….” in the URL above.

    Having genetically high oxalates (AGXT gene) crossed referenced by urine oxalates testing, I’ve not been drawn to use kale, parsley, spinach, or chard in green smoothies, nor do I juice them. However, 4 oz. spring mix or 5 large leaves of romaine lettuce can work well blended into smoothies. I seem to be fine doing this about 2 days a week for several years now.

    As Hashi-hypoT, I’ve concluded over many years that hypothyroid patients medicated with hormones can be less concerned about goitrogenic vegetables since their hormone med takes sufficient care of their thyroid levels. However over-doing anything is generally not a good idea. It’s amazing the number of otherwise-intelligent people who appear to think that “if doing something is good, then over-doing it is better.”

  15. I read the Hubbard study and was concerned about his findings. Especially since I tested positive for somewhat elevated levels of thallium in a provoked toxic metals urine test after having consumed lots of kale and cruciferous veggies. However, it seems that this study is somewhat controversial and the science behind it has been questioned. Regardless, the combination of even somewhat elevated levels of toxic metals in vegetables and someone who doesn’t detoxify well is a recipe for disaster.

  16. I make smoothies out of cooked greens (almost always a cruciferous veggie) exclusively from my personal organic garden in a liquid of bone broth, so I can’t see a problem with what I’m doing. I also eat kelp or dulse and home made sauerkraut or kimchee every day, so I think I’m safe.

  17. I was really glad to see your article. I never glommed onto this dumb fad – I figured out for myself that most greens, the ones you mention, should be cooked or at least consumed only minimally in their raw state.

    All we have to do is see how our ancestors consumed the greens you mention. They always cooked them. They didn’t have “science” in those days, but they figured things out over millennia.

    Bitter or semibitter lettuces are nice uncooked, of course!

    Thanks so much for this article and I hope everyone listens to you.

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