I used to eat this stuff as a normal and healthy thing to do. Swiss chard and I go way back, ever since my mother told me to plant it in my first garden when I was 10 years old. It germinates easily and it isn’t bothered much by pests. The large leaves are easy to harvest and the plant looks great in the garden. And, most important to my mother, it is a cut-and-come-again plant that yields a continual and bountiful crop. It was good that it was so easy to grow, because grocery stores rarely carried it. All that has changed.
Mountains of Swiss Chard at the Store
Swiss chard has grown popular—very popular, if the amount of refrigerated space allotted to it in our local organic supermarket is an indicator. I was there last week on a hopeless quest for mustard greens. I asked the young man restocking the produce case if they had mustard greens, but like the other stores in town, he said they don’t carry them anymore.
Then I noticed that he was unloading swiss chard—at least 40 colorful bunches, fresh out of their shipping boxes into a 4’ 4’ section devoted solely to swiss chard. The greens looked marvelous, but I could only sigh and worry. In my astonishment at the amount of store space devoted just to swiss chard, I commented on it as he piled it up. He said that they sell a “crazy amount of it”, but he’s never tried it.
Hidden Danger: Oxalate
Swiss chard is a hot trend! It has joined the ranks of kale and spinach as top sellers in the fresh greens department. Too bad. Swiss chard is loaded with a natural toxin called oxalate. Just one half-cup of steamed white-stalked swiss chard has about 500 mg of oxalate and ½ cup of steamed red swiss chard has over 900 mg of oxalate.  Steamed spinach has about 700 mg per ½ cup. That is a lot of oxalate.
Doctors and researchers assume you only consume about 120 mg of oxalate per day! 120 mg is about the amount of oxalate in just one ounce of almonds. But, a ½ cup of swiss chard has 4 to 7 times that amount – far in excess of what is considered “typical” and “tolerable” on a routine basis. That half cup of spinach has about 6 times the daily expectation. Oxalates have enormous health consequences: If you happen to like nuts and swiss chard, spinach, or beet greens you could be heading for physical pain, poor sleep, or kidney stones.
Ignoring a Brain Toxin
Until 2009, I paid no attention oxalates in my foods. I did not know or care that I routinely ate foods loaded with oxalate. I never connected my weird symptoms of nightly hiccups, belching, restless legs, and poor sleep to my diet. Why would I suspect my diet? I was eating fresh, whole, healthy foods—all the time, every day. I served swiss chard about twice a week and sweet potatoes at least five days a week, believing they were good for me. My diet could not be blamed for my health problems.
So later, I was shocked when I accidentally cured my sleep problem by eliminating high oxalate foods like swiss chard (including my beloved sweet potatoes). I learned that oxalates are neurotoxic. That is, they bother the nerves and brain. I also learned from reading medical articles that hiccups are a sign of this neurotoxicity (which covers a spectrum of symptoms including hiccups, convulsions, and death). (Here are a few of those articles: Neto 1998; Chen, Chou et al 2002; Chang, Hwang, et al 2000). There must be a reason the bugs don’t mess with the swiss chard in the garden—it may be too toxic for them, too!
The Danger of Innocence
My ignorance about the oxalate content of foods and about the toxic potential of oxalate in foods left me at risk for self-inflicted poisoning. That turned out badly for me, and for my husband. As a last resort, I corrected this dietary mistake and was surprised at the results as we each recovered effortlessly from chronic health conditions.
Anyone can get into trouble from overdoing the high oxalate foods. This is especially relevant now when high-oxalate foods are growing in popularity and are available year round. The produce aisle has become a loaded gun, and we are the innocent kids who have no idea about the dangers lurking there.
Healthy, Safer Greens
If you want to avoid accidental harm from oxalate, drop the swiss chard, beet greens, and spinach. And tell the produce manager you would buy mustard greens (6 mg oxalate per ½ cup steamed) and other low-oxalate produce, if only they would stock them.
Indeed, there are other good options for cooked greens. For example:
- Lacinato (aka Dino) kale (4 mg ox per ½ cup cooked),
- green cabbage, cooked (4 mg ox per ½ cup),
- arugula, cooked (7 mg ox per ½ cup),
- turnip greens (10 mg ox per ½ cup steamed), or
- dandelion greens (10 mg ox per ½ cup steamed).
Many raw salad greens are also safe:
- romaine lettuce (0.5 – 2 mg per ½ C),
- mache (corn salad) (0.4 mg per ½ C),
- watercress (2 mg per ½ C), and
- arugula (0.7 per ½ C).
What mustard greens and romaine lettuce lack in hipness and glamor, they make up for by letting you sleep at night!
- The values of oxalate content presented here are based on testing performed at the University of Wyoming in Laramie on behalf of the VP Foundation. http://thevpfoundation.org/vpfcookbook.htm
M. Wieland says
What about baby kale; is it also high in oxalates?
Sally K Norton says
The testing of various kale varieties (none are “baby”) suggests that the green kales range from 8 – 18 mg of oxalate per cup. 56 – 76% of the oxalate is a soluble form. The soluble fraction is the part that tends to get absorbed into the body. Dino kale (also called Tuscan kale, lacinato kale, or black kale) test results suggest that it is low oxalate – 2-10 mg per cup when raw and 3-7 mg when simmered and drained (1 cup volume after cooking). These numbers come from data reported by the VP Foundation. One test of purple kale showed that 93% of the oxalate was soluble. This test result was reported by the Autism Oxalate Project.
For context: A low oxalate diet aims for a daily total of 50 mg. day (about 15 mg per meal). A hypothetically “typical” oxalate diet is 3 times that much or about 50 per meal. A salad made with one cup of raw baby spinach has about 300 mg oxalate (or 6 times the amount that researchers think you are eating per meal). If you love kale, Dino kale is your low oxalate choice.
Thank you for that timely and very helpful response!
Here I’ve been having raw chard in salads and sandwiches every day for almost 2 weeks. My sleep has been awful and the last salad burned my throat so bad, I knew something must be off. Thanks for this article – it seems like this oxalate issue goes mostly ignored by grocery stores and health food blogs. Hopefully I can heal quickly as you.
Sally K Norton says
I’m glad you are learning about oxalate and swiss chard being horrible for us! I’m glad you think 5 years is a quick healing! I feel like I am 35 years younger now, but the process was bumpy. Our inattention to this is tragic, given how easily we could avoid oxalate related health problems.
Laura Weir says
also are organic hemp hearts high in oxalates. Thanks for any info on this
Sally K Norton says
Hemp hearts from Manitoba Harvest were tested back in 2014 by the Trying Low Oxalate group (Autism Oxalate Project), and they were fairly high (78 mg per 100 grams, of which 38 or 50% is soluble, meaning 50% is easily absorbed into the body).
Bob’s Red Mill Hemp Protein powder tested even higher in oxalate (104 mg per 100g). You could probably use hemp seeds in very small quantities (a tablespoon, 9 grams, is about 7 mg total oxalate). Keep in mind that all seeds are difficult to digest. Sprouted seeds are better in terms of phytates but other anti-nutrients like oxalate are generally not reduced by sprouting.
Boiling swiss chard and beet greens for 6-8 minutes can reduce oxalates considerably. It has made a big difference for me. I dont feel the side effects any more.
Sally K Norton says
That is really interesting that you notice a difference with less symptoms if you boil these high oxalate greens. For me, your observation does raise the question: Could it be that the oxalate that is leached out from the boiling process is the very same oxalate (fraction or variety) that would otherwise be most easily absorbed or be most noxious to your digestive tract? Impossible to know, perhaps, but within the realm of possibility. It is also possible that some other compound other than oxalate (tannins? there are thousands in plants) that was causing your immediate symptoms.
Here is some info on the testing of cooked vs raw chard:
Testing performed at the University of Wyoming and published in 2005 found that a full 12 minutes of boiling (timed after the full boil was achieved) did change the oxalate content by 63% and 65%. That sounds impressive enough.
Red chard leaves (similar to Beet Greens): total oxalate changed from 1170mg raw to 430mg after boiling; soluble oxalate changed from 810mg to 120mg after boiling.
White stemmed /Green chard leaves: total oxalate changed from 960mg raw to 335mg after boiling; soluble oxalate changed from 620mg to 98mg after boiling.
It’s good that you are boiling your veggies. With broccoli and Brussels sprouts, a 12-minute makes a very meaningful difference. Take a look at that data:
Broccoli total oxalate changed from 14mg raw to 5mg after boiling; soluble oxalate changed from 5.3mg to 2.3mg after boiling.
Brussels sprouts total oxalate changed from 15mg raw to 6mg after boiling; soluble oxalate changed from 10mg to 2.6mg after boiling.
The main drawback with a 12-minute boil is that your broccoli became mush at 4 minutes, and by 12 minutes you have soup suitable for a toothless person.
Keep in mind some key points.
1. Symptoms are not always a reliable indicator of the effects of eating oxalate. If they were, it would be easier to identify oxalate as a disease-causing agent, and this oxalate problem would be common knowledge. The various problematic effects of oxalate don’t always generate symptoms (on the way in, or when stored by tissues), especially when you are keeping your intake at a moderately-low level. In fact, oxalate accumulation in the body is a notoriously low-to no symptom problem, until it finally breaks though as kidney stones, chronic constipation, or arthritis, or mental fatigue. Even then, no average doctor would tell you that these problems had any connection to your vegetable selections.
2. You are boiling for 6-8 minutes, which perhaps would remove a somewhat smaller fraction of oxalate, as was the case in the study by Savage et. al. in New Zealand. They boiled beet greens for 8 minutes and found a 17% reduction in total oxalate (from 792mg/100gm raw to 660mg/100g boiled).
3. A level of 430mg (120mg soluble) in 12-min-boiled beet greens or red chard, and 335mg (98mg soluble) in green chard are still extremely high oxalate levels in these foods. High enough to be a concern for anyone with digestive issues, pain, fatigue, or a history of UTIs, irritable bladder, or kidney stones.
4. The longer the cooking time, the greater the loss of other minerals in those foods
5. Most other greens (except spinach, sorrel, purslane) are low in oxalate. I would suggest you select them as safer alternatives. Examples include lettuce, watercress, arugula, cabbage, turnip greens, mustard greens, most kales, even pea greens.
Chai, W., and Liebman, M. (2005). Effect of Different Cooking Methods on Vegetable Oxalate Content. J. Agric. Food Chem. 53, 3027–3030.
Savage, G.P., Mason, S.L., Vanhanen, L., and Busch, J.M. (2004). Oxalate content of raw and cooked silverbeet. Proceedings of the Nutrition Society 29, 27.