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. Lorna says

    Thank you for this great blog post and all the comments.
    I have a question.
    If you are not supposed to use the water that the greens are blanched in because of the acid in the water, what happens to the acid when you cook them in other ways like frying etc? Thanks.

  2. Suz says

    Thank you so much for sharing this information. I was getting back into Green Smoothies for the summer and this came at the perfect time.

  3. Traci says

    Thank you for getting this information out to people. I was juicing kale and spinach for years and was constantly battling kidney stones. I do miss my green drinks but I do not miss those painful stones. I might try your suggestion about blanching the greens first.
    Thanks again,

  4. Evelyn says

    I would tell you to watch out for the ready made drinks B-12.
    The form of B12 that you’ll find in most B12 products – even the B12 injections your doctor may administer – is cyanocobalamin. Can you guess how this form of B12 gets its name? Cyanocobalamin is comprised of a cyanide molecule attached to a cobalamin (B12) molecule. Cyanide is a toxic poison that the body cannot metabolize, and over time, it can accumulate in brain tissues with disastrous results.[17]

    For reasons I’ll never fully understand, way too many B12 supplements on the market today are made with this virtually worthless form of B12. My guess is that these companies are just out to save money at the expense of your health, which is truly a shame.

    What you want to take is a supplement made with the methylcobalamin form of B12, which research has shown to be the safest and most effective.

  5. Vicki Sawyer says

    Very interesting information…thank you. I have recently started drinking the Naked brand Green Machine drink for breakfast or lunch. How would you rate this for someone who does not do much cooking and is trying hard to improve her diet, lose weight, and improve her health?
    Thank you,

  6. Joy says

    Thanks for this article. I make a spinach smoothie for my kids every day after school, and one of the children has recently been complaining of moderate and fleeting low back pain, with no other symptoms. Makes me curious as to whether it could be the spinach and his kidneys…. If we start steaming , can the affects of oxalic acid be reversed?

    • Dawn says

      Lots of water to help flush out any accumulation (approx. 6-8 cups a day in non-sugary food and beverage form). Or you could add dandelion (Taraxacum officinale) to your smoothies for a bit to help the kidneys flush and strengthen them at the same time. There isn’t too much of a concern about needing to “detox” or anything. Your child may just have been experiencing a mild irritation from these acids, not necessarily any type of syndrome. Some are more sensitive to them than others. Changing the family’s habits when it comes to raw greens will most likely be all you need to see the recurrent irritation disappear.

  7. Sandi says

    Wonderfully useful info – thanks! However, I would like to clarify something… steaming and blanching are NOT the same thing and the two tems shouldn’t be used interchangeably. A steamed vegetable does not touch the water but is in a steamer basket or strainer ABOVE the boiling water so it is cooked by the steam. A blanched vegetable is submerged IN the boiling water. The instructions say blanched, and rightly so, but the word steamed is used throughout the rest of the blog, which can be confusing.

    • Dawn says

      Right you are Sandi,
      I use blanching in the recipe because it is the best way to prepare your greens for freezing. I use steaming throughout the rest of the article because you can either steam or cook (blanch, saute, fry, bake, etc.) your greens to deactivate the oxalic acid. I often steam them and then use them in a smoothie and don’t freeze, so I believe I put the two together just before I introduced the recipe. Sorry for the confusion!

  8. jules says

    Hello, I am new to smoothies since having my gallbladder removed. I have read all the comments and am more confused than ever. I thought if you steam something it takes all the goodness out of it. I don’t eat much at all so use smoothies to keep me from not eating at all. The talk of kidney stones scares me I have already had my gallbladder removed. I might just steer clear of greens in my smoothies and just have fruit ones. Thanks for the information.

  9. Trish says

    Oh no! I have been blending and drinking green smoothies weekly for a long time. I use what is in my garden. Usually beet greens, chard, spinach , kale, mint, parsley, and stevia. If I omit the raw kale and spinach are the rest okay?

    • Dawn says

      Trish, unfortunately the beet greens and chard are also oxalic acid culprits as well. You may try steaming a blend and adding it or try rotating greens as others have suggested. I don’t know what I think about that as I haven’t seen the studies that support that idea though. In my house I would use all four of those greens sparingly in their raw form and steam/freeze them more often.