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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.

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.

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Join the conversation

  1. Thank you for including oxalate as an important concern and reason for caution and hesitation around green smoothies (and juicing too). Fantastic! The unbridled promotion of smoothies is based on a faith in fresh plant foods that lacks any meaningful scientific backing or consideration of possible harms.
    You are right that oxalate fosters inflammation and related troubles beyond the kidneys and urinary tract. Oxalates can play a significant role in problems with chronic pain, digestion, connective tissue instability-i.e.: osteoporosis, and autoimmune diseases. Oxalate also contributes to mineral deficiencies and calcification in the soft tissues of the body, including plague in the arteries.
    And, you don’t need a juicing or smoothie practice to overdo oxalate, because nuts, beans, potatoes, bran, chocolate, tea, and many spices are also loaded with bioavailable oxalate. Given this fact and the lack of any real study, it is unlikely that rotating in low oxalate greens is any guarantee of keeping oxalate intake under 250 mg/ day. Plus, it is the occasional high oxalate meal that can set the stage for a persistent problem of oxalate accumulation in the body. (I discuss this problem in my recent article: http://jevohealth.com/cgi/viewcontent.cgi?article=1085&context=journal )
    Along with many other factors, genetic variations likely influence not only how oxalate impacts your health, but how much oxalate you can tolerate in your diet before trouble erupts. The many moving factors influencing the effects of the oxalate you eat are complicated. The biggest complication is that oxalate can damage your health and function in a fairly silent fashion – not unlike the period of silent formation of kidney stones – they don’t hurt until they move, even then, they don’t always cause noticeable or severe symptoms. Symptoms or not, oxalate does impact your tissues and long-term wellbeing in serious ways that are under appreciated in medicine and public health. I thank you for mentioning it here.

    Chris, I have to ask you to please be careful with lists of high oxalate foods. Your list of 9 items within the text of this article includes cabbage. However, cabbage one of the lowest greens at 2 mg of oxalate per ½ C raw (The VP Foundation Newsletter, The Low Oxalate Diet Addendum Summer 2012 p. 23.). Unfortunately, this type of error is endemic in peer-reviewed academic articles too (including the ones you cite), contributing to mass confusion about what foods are low or high in oxalate. Casual, error-prone, partial food lists can be distressing and harmful to those who need reliable information to manage oxalate in their diet.
    Please be aware too that supplementing with Lactobacilli and Bifidobacteria has not been proven to assist with the tolerance of a high oxalate diet. Whatever help this might be is limited by several factors: 1) these healthy flora reside chiefly in the colon, but oxalate absorption can occur anywhere along the alimentary canal, beginning in the mouth and stomach (where the acidic environment may promote the movement of oxalate ions into the body); 2) colonization of healthy bacteria is somewhat dependent on a whole ecosystem of gut flora which is disrupted in most of us; and 3) excessive amounts of oxalate in the gut can kill off these same bacteria.

    Please continue to inform your readers about oxalate. Tell them: anyone could get into trouble with oxalate, and the most health conscious among us may be most at risk. The unnoticed, subtle, or even invisible symptoms of oxalate accumulation make it difficult to know when oxalates are a problem for any given individual. You might not realize the damage being done until you become very ill. It’s so sad that lost vitality, disease, and damaged kidneys can be the unintended consequences of sincere efforts to be healthy.

  2. I’m all for eating meat and avoiding green smoothies (just to be on the safe side).

  3. Hi Chris

    Thank you for this article. I have enjoyed green smoothies and eat alot of these types of vegetables as well. Would you be able to tell me how to get oxalates and thallium tested.

  4. It says here that “Cooking cruciferous vegetables stimulates the production of an enzyme called myrosinase that helps to deactivate goitrogenic glucosinolates.” However, in the cited article (abstract) it says, “it is suggested that this lack of activity of cooked Brussels sprouts is due to inactivation during cooking of myrosinase, the specific glucosinolate-degrading enzyme,” which clearly implies the exact opposite and is in agreement with everything else I have read about myrosinase being inactivated by cooking.

    • Steaming, more so than “cooking” does the same thing. I thought that was common knowledge among the health-food aficionados. Consuming GREENS “raw” was not advised… going back as far as Adele Davis.

  5. The following comment appeared here:

    “People who have certain illnesses benefit from smoothies in all kinds of ways I won’t go into here”.

    I very much want to know what illnesses benefit from smoothies that no other method can provide. Can someone enlighten me? Thanx.

  6. What I would like to know is if you are taking thyroid hormones, is it okay to take iodine or eat kelp also.

    • Google this question. There is a spectrum of beliefs on this but my personal experience was that taking a drop of Lugol’s Solution daily was putting flames on the fire of my autoimmune thyroiditis. I did serial measurement of my thyroid antibodies and they climbed up 10-fold in the brief time I took iodine. Thyroid hormones contain iodine but I’m not sure if this is a significant source of iodine.

      I wouldn’t have kelp more than once a week e.g. sushi. I have a miso soup with kelp about once a week and have iodised sea salt. I have read a teaspoon of this daily will give you sufficient iodine stores. Unfortunately in my ignorance in years past, I moderated my salt intake. Not a good idea for a New Zealander as our soils are deficient in this, selenium and molybdenum.

  7. Among all you health-conscious people here, nobody mentions – and Chris only did sort of – that the GREENS in question should only be consumed as ORGANICALLY grown. Many are listed being among the “Dirty Dozen” = meaning are highly polluted with pesticides, etc., if you buy them commercially.

  8. What about microgreens? My understanding is that the antinutrients are much lower in microgreens than in mature versions of the same plant. Plus, there are a lot of microgreens that are not members of the brassica family, like sunflowers and the numerous types of lettuce.

  9. What about drinking ‘green drinks’ made out of the powdered vegetables and fruits? Does it depend on if the foods were cooked before being ground down?

  10. This is a shocker! Green smoothies are so famous as a diet food, everybody is having them. I had started consuming these since a month ago, I had no idea they could have side effects! I will definitely quit them now, they don;t even taste good!

    • Try eating those veggies in a salad, with some olive oil, garlic, natural vinegar, pepper, etc. Then, eat those delicious ripe berries on their own, not emulsified with kale and beets. They will all taste wonderful! How can anything taste good when you smoosh a bunch of incompatible ingredients to a vile-tasting slurry? Plus, when you eat the veggies and fruit in their natural, solid form, your appetite will be more satisfied. What’s next? Dinner smoothies? Put 4 oz of grass-fed steak, your salad, and your grilled veggies into the food processor. Add your salad dressing and pulse into a smooth glop. Slowly add a glass of red wine and blend until you have a nice, smooth slop that a hog wouldn’t touch. Yuck!

      • Hi Annie Laurie, I laughed, too, reading your post. I support your comments. I have tried to include green smoothies in my diet, but it just didn’t seem natural at all, not even as a breakfast option. I love blueberries, but taste wise they seem wasted to me in a smoothie, as you don’t feel the taste of them at all. I eat all of those vegetables listed by Chris, but either steamed, stir fry or in salads, sometimes raw, sometimes cooked. Cheers! Cristina M.

      • Unless you’re one of the rare individuals who have esophageal strictures that make pureeing food a necessity if you don’t want to spend 18 hours a day chewing your food into a puree. It’s a survival strategy when you have difficulty swallowing.

        • As a matter of fact, I DO have a hereditary esophageal constriction. It necessitates that I chew my food adequately, and eat in a relaxed mode.
          Both these are things, of course, that we all should do. On the rare occasion when I eat too fast and do not chew adequately, I regret it. However, it does not take 18 hours a day to do this. I highly doubt, although I have never timed it, that the chewing takes as much as 18 MINUTES a day. If chewing food adequately takes someone 18 hours a day (obviously a gross exaggeration), how dang much are they eating???

    • I can’t imagine consuming most of the green smoothie recipes I see others gulping down. Such a ghastly combination of things that just don’t go together. Why not just place them on your plate and eat them the normal way.

      • Exactly! I see some people are putting avocados in their smoothies. Avocados, really!!??? At close to 2 bucks for a little avocado, I am going to ripen it perfectly and enjoy every creamy, heavenly microgram, savoring the taste and eating it slowly. And strawberries? They aren’t cheap, either. What beats the taste of ripe, succulent strawberries? That is also something to be savored, slowly and mindfully. Eating is one of life’s greatest pleasures. Of course, maybe the smoothie fanatics have never tasted the unbelievable deliciousness of some of these fruits and veggies. Why treat some of the most wonderful-tasting foods on earth like cod-liver oil, where one might want to mask the taste?

        • LOL. I hope we’ve converted a few people here to trying the strange practice of – wait for it – EATING. You are right about strawberries, that is for sure. I work like an animal picking them on the farm and believe me, I am ready to burst a few hours later from “tasting”. More in my stomach than in the bucket.

        • “Some people” would be me. I put avocados and strawberries in my smoothies and drink them. It has nothing to do with masking the taste. I also eat avocados and strawberries (with my teeth), just like you. Most people who drink green smoothies also eat meals where they actually chew their food, the smoothies are one small part of their daily food intake. People who have certain illnesses benefit from smoothies in all kinds of ways I won’t go into here. Maybe you don’t have those illnesses. It’s easy to make fun of people and feel like a “superior eater” when you don’t know all of the details about why people do what they do. I think it’s safe to say that everyone commenting here knows how to enjoy, chew, appreciate, and savor different fruits and vegetables just like you do.

          • Preach it Karen! I chew fresh veggies all day, but like to supplement with green smoothies and other veggie laden beverages because I am trying to add as many vegetables and calories as possible. Sometimes I’m out of time, my jaw hurts from chewing, or I’m so exhausted all I can do is drink my food. Though, when I have fresh strawberries and perfectly ripe and delicious avocado, you better believe I want to be tasting those on my tongue and not in my smoothie. I certainly will be using this new information to inform my green smoothie consumption though.

    • The traditional (folk) method of preparation is to boil the kale in lots of water and then throw away (onto the compost pile, or use to water your plants) the dark yellow water it was cooked in. Tried & true & good for you. Probably better than raw or lightly-sauteed.

  11. I’m wondering about spinach. Should it be cooked or eaten raw? I recently read if it’s cooked that’s when you have the oxalate problem?

  12. Does the same apply with cucumber and cilantro? (Organic) I have sulphur issues so I don’t do kale etc anyhow but given cilantro is good for detoxing I wondered if the same thing applies?

  13. I just found some info on a person’s experience in drinking high oxalate chard juice – and how he neutralized it. He added rejuvelac, a cultured probiotic-rich drink made by fermenting freshly sprouted grains in water. Here is where I got this info:


    Nevertheless, I won’t be juicing my greens anytime soon, except maybe for adding some romaine lettuce to some fruit juice to cut the sweetness. I still think that greens should be eaten (you know – where you use your teeth) and most of them (obviously not lettuces) should be cooked first and, as done traditionally, consumed with dairy product. In every older cookbook I have, spinach or swiss chard are made with cream or cheese one way or another. I guess that this, being an old practice, was a way to deal with the antinutrients.

  14. Amazing how everyone who’s addicted to them comes out in their defence… Attacking Chris for the information, ridiculing because… well it’s just like eating a salad… or asking, but if I just do this, it’ll be ok, right?

    Why is it so difficult to get?

    A regular dose of raw ‘greens’ blended up and drunk is neither Paleo, not recommended by Traditional Chinese Medicine. It’s not natural food and is not what our ancestors would have eaten!

    If you don’t like ‘hearing’ that your precious green smoothie might not be healthy, you have issues!

    You could just leave the greens out, OR eat like your ancestors and EAT a variety of ‘some raw, some cooked’, seasonal foods, instead of the same raw blended greens every day.

    • Right on Lucy. Some folks just prefer to live in the realm of Confirmation Bias. Its a right turn, then another from Alternative Facts County.

    • We are not attacking Mr. Kressler. We are saying that his article takes a negative approach to green shakes. It is one thing to give the information re Kidney stones, etc and cruciferous vegetables and shakes. It is another thing to instill fear about eating or crushing them. A kale shake with lemon w or 3 times a week does not have the effects he names. Everyday use however would, like everyday use of almost any food. My suggestion is that Mr. Kressler approach writing us information with a more positive approach.

      • Why should Chris write his information “with a more positive approach?” For your benefit? He’s doing all of us a great favor with it, that is, all of us who are not afraid of “reality intrusion!”

      • Sublime…thats silly. Would you find a more positive approach to a smoking warning acceptable? Not everyone who smokes gets lung cancer, etc…so “maybe its sort of a health issue, but not always…” ?

        A more positive approach is spinning to make some people feel better about their chosen activities and dietary choices, not provide a useful data backed commentary…on a diet-fad. A fad with little scientific research. Just mostly celebrities, and tabloid magazine support…and of course those who sell mixers, juicers, etc. Nutri bullet does not have labs, or lab-coated researchers on their payroll!

        Can you prove that over time, consuming 3-ish times a week wont add up to the issues presented! Maybe its okay to smoke a few times a week…

        Youre deep in the self diagnosis, self prescribing camp.

        And what exactly would be “a more positive approach” wording..?

  15. This is absolutely obnoxious. Not saying green smoothies are healthy but to demonize a recipe that calls for 2 cups leafy greens (average salad) and one cup broccoli (average side for lunch or dinner. Any paleo template eater can eat this on a regular basis while making zero smoothies. Yes. Smoothies are easy to over consume. But if that recipe is considered troublesome to have once daily (yes most people are not drinking more then one smoothie, I don’t care about your one outlier friend who drinks 7 a day) then every person who strives to follow a paleo type diet who reads Kresser, MDA, etc easily will be in equal trouble eating a “big ass salad” daily and a side of broccoli, cauliflower or some sauerkraut. If anything. The average paleo type will eat more then what’s in that recipe.

      • Yes, I’ve been scoffing home-grown perpetual spinach and chard as a nod to Dr Terri Wahl’s automimmune paleo diet and my thallium levels are up. I need to get my soil tested. My partner keeps chanting that industry may have taken place on this site and he’s nervous about eating the garden produce.

        7 years ago 200 bricks exploded onto the garden from our western house wall in a 7.1 richter scale earthquake and there were bits of mortar in there that I picked out but who knows?