Are Raw Green Smoothies Really Healthy?

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Kale Smoothie

Recently I was giving a talk on spring greens to a gardening group in my community. I was extolling the virtues of dandelion (Taraxacum officinale), so I wandered into my usual semi-rant about people eating raw greens. Dandelion doesn’t have any oxalic acid in its greens, so it can be eaten without irritation. In contrast, spinach and kale do. Spinach contains much more than kale, but nonetheless, both should be eaten raw only sparingly.

Eating a Raw Spinach or Kale Smoothie?

When I was a teenager, spinach salads were all the rage. We learned through the diet gurus of the time that no one should be caught with regular lettuce in their salads. Instead, it was much healthier to use spinach as our raw greens. Recently, the kale smoothie has caught on. I’m not quite sure where that leaves spinach, but I suspect it’s not going anywhere.

The truth is that both spinach and kale are very healthy for you. Unfortunately, it really needs to be steamed before it’s eaten. Steaming or cooking deactivates the oxalic acid content that they have, making them more nutritious. Oxalic acid binds with the calcium in our food making it unavailable for digestion. Over time this can lead to a plethora of health issues, osteoporosis among them. The acids can also irritate the kidneys.

After I finished speaking, a woman approached me. She shared that she had been having the same breakfast smoothie every day for a couple years now. At about the same time each day she began to have pain in her kidneys. She had been to several doctors who had not found anything specifically wrong, and yet the same symptom appeared every day like clockwork a couple hours after breakfast. Her smoothie was made with raw kale.

How to Use Greens in a Smoothie

Does this mean that everyone should stop using spinach and kale in their morning smoothies? Absolutely not! I LOVE to mix greens and fruit in a smoothie. It’s a delicious way to get a powerful punch of vitamins and minerals.

To use greens in your smoothie you just need to steam them first. This may seem like a strange texture, but bear with me. Usually, we make smoothies when we are on the run. There isn’t enough time in the morning to steam your greens and add them into the blender. Instead, I like to steam enough for the week and then freeze a supply. Each morning I take a handful of frozen greens from the bag. They not only add the nutrition I want, but I also don’t have to add ice cubes.

How to blanch your kale and spring greens

  1. Set up a pot of boiling water with a steamer basket insert.
  2. Fill the steamer basket with your greens and immerse them into the boiling water.
  3. Blanch for 2 minutes.
  4. Remove the steamer basket from the boiling water and immediately plunge into an ice water bath.
  5. Remove the steamer basket from the ice water bath and put the greens into a strainer to drain.
  6. After they are well drained, move the greens to a clean, dry towel. Pat dry as best as you can.
  7. Spread the greens out onto a tray and transfer to the freezer.
  8. Once frozen, the greens can be broken up and placed in a zipper top freezer bag for storage in the freezer. The small chunks of greens are easier to portion out for small recipes or smoothies than if you had just placed the wet greens into a freezer bag and frozen them as one large chunk.

Be sure to label your greens so you know what you are reaching for. If your freezer is anything like mine, once these early spring harvests go in they look like everything else!

Are you eating raw green smoothies?

If so, did you know about the importance of steaming your greens first?


About Dawn Combs

Dawn is a wife, mother, farmer, author, ethnobotanist, professional speaker, and educator. She has over 20 years of ethnobotanical experience, is a certified herbalist, and has a B.A. in Botany and Humanities/Classics. Dawn is co-owner of Mockingbird Meadows Farm. Her books include Conceiving Healthy Babies and Heal Local.

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  1. Hannah says

    Thanks so much for this! I love smoothies, and just bought a bunch of greens to try out different ideas for integrating them. Carrots and Kale are on the list!

  2. Kaye says

    Love this article! Yes, it IS true that you can reduce the oxalic acid in these food by boiling them first. Unfortunately, you cannot keep the water you used for boiling as the oxalic acid goes out into the water. Your boiled greens must be rinsed to get rid of the oxalic acid. I love the idea of blending them and freezing them into ice cube trays! Using fresh water, instead of the water they were boiled in will fulfill the desired goal of less oxalic acid!

  3. Mary Wimmer says

    I add two cups of boiling water to the handfuls of raw kale or spinach and let it sit for a few minutes before adding the other ingredients and blending – that way the water soluble vitamins aren’t lost in the steam or left behind in the water 🙂 enjoy!!

  4. Mary says

    I started using frozen spinach in my smoothies because fresh would go bad before I could use it all. It’s nice to know I was doing the right thing all along!

  5. Dave Parrent says

    Do you know if the action of drying kale or spinach eliminates the problems with oxalic acid? I have dried kale (coated with a bit of olive oil and sea salt) to take on a backpacking trip as a snack.

  6. Dr Wendy Dearborne says

    Excellent blog! It addresses an important issue with RAW green smoothies! As an author of a book and expert on green smoothies, it is not necessary to steam your greens to deactivate the oxalic acid. In fact, steaming will destroy some vitamins and minerals present in your green leafy vegetables, it will not deactivate the oxalic acid. If you are wanting to consume green smoothies daily, you need to ensure that you frequently rotate the greens that you’re choosing to use. This is the way to prevent any issues that may result from over usage. Also, your body gives you natural signals when you have over used a particular green leaf; nausea, bloating, joint pain and disinterest to name but a few. It’s also important to point out that all fruits and vegetables contain oxalic acid…so do we as humans. So, if you are a green smoothie drinker…remember periodically rotate everything you are blending.

    • Brenda Quick Hedstrom says

      Thank you for your addition to this conversation. I find this information quite interesting. I have been using kale, spinach, collards, arugula, just about any green I can get my hands on to put in my smoothies. I eat them everyday and have for three years. I have suffered no ills. As a matter of fact, I have been able to completely stop taking calcium suppliments which is important as a post menopausal woman. If it is important to blanch or steam these greens, should we stop eating salads? I think we all need to do what works for our own bodies. There is never one solution for all.

  7. Charlotte says

    Dawn said “That is yet another example of the natural defense that plants put together to keep ruminants from mowing them down.”

    I believe our Creator designed a little bit of different “poisons” into plants so critters would not exterminate a whole species. Also, the Victoria Boutenko family, (the green smoothie lady) learned about eating kale day-after-day for three months. They all became sick. So the trick is to not eat the same green continously! Simple. I have been alternating betweens raw Vitamix blended greens on a weekly basis for years and never had a problem.

  8. Kelli says

    I REALLY appreciate this article!! I followed the trend of green smoothies faithfully for two years. With a ton of kidney pain, I went in to the Dr. and they found that I had an 8 mm kidney stone. (I was able to pass it with natural products instead of the insisted surgery, yay!)
    When I got pregnant, the thought of a green smoothie made me gag so I stopped drinking them. Somewhere along the way, I was drawn to a list of things that contribute to kidney stones. Sure enough, spinach and kale were on the list. I was glad I had stopped! However, I have had my baby and in the interest of getting rid of the baby weight and my tastes changing again, I am wanting green smoothies. This article makes so much sense and is very timely. I will be sure that throwing raw spinach and kale in the smoothie is on a rare occasion. Thank you so much!

      • Kelli says

        I used Chanca Piedra. It took patience and diligence, but I know it worked! You can google it for lots of testimonials. That’s how I made my decision to try it 🙂

  9. Ginelle says

    Hi! This is some interesting info. I would like to see your sources for you info, though. Could you post them please? In the spirit of learning (and respect), I would like to read these sources for myself. (Please, do not take this as an insult or that I don’t think it is credible. I just like to get as much info as I can and, since I have never heard this, I would like to read more. Thank you for your time).

    • Dawn says

      Hi Ginelle,
      I’d have to send you a bunch of book titles, but I’ll start with one off the top of my head- Nourishing Traditions by Sally Fallon.

      Dr. Weil has a great article online-

      Here is one that is solely concerned with disproving an association between oxalic acid containing foods and kidney stones. It is very useful if you’re a researcher though because it does go into some of the benefits we see with a small amount of ingestion of oxalic acid. I would also point out that most of the kidney stone correlation that we see is with folks who consume a high amount of vitamin C in conjunction with a high amount of oxalic acid. They can still prove to be an irritant to the kidneys either way… but in the interest of playing devil’s advocate in your research…

      As you research, be aware of who is writing… someone who is pushing a smoothie lifestyle may be more interested in “proving” that using raw greens aren’t a bad idea. While I tend to stay away from suggesting wikipedia as a source, they have a nice chart of foods and their oxalic acid contents if you google “oxalic acid”.

      Hope that’s enough to get you started, but let me know if not!

    • laura woodford says

      There are some great websites about people with thyroid issues. for one.

  10. Mike says

    Great article Dawn, thanks. Green smoothies are definitely a favorite of mine! I like my romaine lettuce. What are your thoughts on Goitrogens and thyroid suppression being more of the concern with raw kale as opposed to the lower amount of Oxalic acid in it?

    • Dawn says

      Yes, that would be another concern for me. That is yet another example of the natural defense that plants put together to keep ruminants from mowing them down. Goitrogens are also deactivated with heat, but usually need to be eaten in large amounts by people who are already deficient in iodine and/or selenium to be a big issue. Definitely something to keep in mind!

  11. Melissa says

    We juice everyday and use kale and spinach daily. Is juicing the veggies harmful too??

    • Dawn says

      Juicing would not reduce the oxalic acid content as they would still be “raw”. Again, a little and occasionally would not be a concern…. if you’re juicing these vegetables often I would find another way to include them.

  12. Marisa osodo says

    Glad to contribute to this discussion soon after signing up to this website just a few days ago.I come from a country where Kale is consumed in big quantities. It is actually a national vegetable,and the Swahili word for kale is “Sukuma wiki”
    I must say even at home in Kenya it is never eaten “raw”.Generally food tends to have a better taste when cooked rather than eaten raw.To cook sukuma wiki, it is steamed in boiling water for not more than 5 min, after which it is mixed with fried onions and tomatoes and a little salt to taste.Some people might want to add, cream, peanut butter or coconut milk if they want. It can be eaten as it is or served with any carbohydrate food available. Enjoy a great Sukuma wiki, Kale day!

  13. Danny Fisher says

    I buy and use a powdered raw greens formula in my smoothies. Are these formulas generally blanched before being dried?

    • Christine says

      Danny – typically processed raw greens are cooked at low heats for a long period of time (a dehydrator is specifically used for raw products) which should help against the oxalate count.

  14. Gabie says

    Thank you for the insight! I don’t have one often but certainly this will make it more convenient and healthier … who needs more health issues as a byproduct?

  15. sherri says

    Well, this explains a lot about what might be going in in my body! Thank you for the info! Another alternative would be to stream the greens, blend the greens with the water it was steamed in and then freeze in ice cube trays.

  16. Shelley says

    I had heard this before, but I also heard from another source that it’s ok to eat spinach and kale raw. I have been drinking green smoothies with raw kale or spinach, but only occasionally, not every day. Sometimes it does feel as if I don’t feel right afterwards, so I am thinking your advice to steam and freeze sounds right. Thanks.

  17. Isabella says

    I usually make smoothies with frozen fruits, and only add in a handful of raw greens. Should I still be steaming my spinach, or does this apply only if you are making a fully green smoothie?

    • Dawn says

      It applies any time you are using a green that contains oxalic acid. A bit of them raw occasionally won’t hurt, but if you are using them everyday you can create an issue.

  18. Marie Ernst says

    I have been blending a combination of herbs (sage, 2 mints, oregano, lemon balm, French sorrel) from my garden each morning, along with yogurt, flax and chia seeds. It gives a powerful punch, but this article sets me to wondering if there are some cautions in these ingredients as well.

    • Dawn says

      Marie, the only one in that list I might watch is the french sorrel. Most of the sorrels contain oxalic acid which is what gives them that tart flavor. I wouldn’t worry about a little bit of sorrel, raw, here and there. If you’re using it every day though it might be worth mixing it up a bit and steam/freezing it for your blender like I suggested above.

    • laura woodford says

      you should google cruciferous vegetables. mostly these include broccoli, kale spinach, cauliflower, brussels sprouts, etc. they dont include herbs per se.

  19. Claudia says

    Very good to know. I just bought a Vitamix so this information is very timely.

  20. Michele says

    I have never heard of the need to steam them before! This explains so much. Thank you for letting us know!

    • candace says

      I have also found out that if you have thyroid issues eating raw greens is not a good thing.Also cruciferous vegetables should be cooked before using.

      • laura woodford says

        I just read about that as well, but heard about it a long time ago from doctor. He said eat those veggies in moderation, as well as avoiding too much soy. these can block thyroid hormones. now i use lettuce instead.