Thursday, January 17, 2013

Spinach: the gritty truth

You may remember when supermarket spinach was a recognizable plant, with leaves attached to stems. You dunked and swished it in a basin of water and the grit would fall from the crinkled leaves. You would separate the leaves from the stems, tossing the tough, fibrous stalks into the garbage and chopping the not-so-tough stems for cooking. A second dunking and swishing followed and maybe even a third. But still, a grain or two of grit would sometimes spoil the sensory feel of eating the soft green leaves, steamed for only the number of seconds it took for them to wilt.  

I always supposed that spinach was grown in sandy soil, and that the grit that clung tenaciously to the savoyed leaves was sand that resisted my dunking and swishing. But now, as I harvest spinach leaf by leaf throughout the winter months, I have reason to doubt that assumption. The first leaves of fall are rounded and tender—the same as the baby greens pre-washed and packed in 5-ounce bags and shipped from California (but they hold their freshness for days longer … without irradiation). As the weeks pass the leaves change their shape; they acquire waves and ridges, and develop a more substantial feel. At some point in their maturation, I begin to feel a grittiness on the backs of the leaves, even though my soil is not at all sandy. When I examine the leaves very closely I see constellations of crystals concentrated on the leaf veins, and spreading outward. Spontaneous eruptions of salt.
Do you see the crystals?

I now suspect that some of that grit I was unable to wash off came from the spinach leaves themselves.

Spinach is renowned for its health benefits—its vitamin A content is through the roof, and B9, C, and K amounts are more than respectable. But there’s one nutrient spinach does not offer us, even though it has plenty of it, and that is calcium. The calcium robber—otherwise known as the antinutrient—is oxalate, an organic acid contained in fruits, vegetables, nuts, grains, chocolate, and even in our own bodies. 

(Our cells produce it and it’s in chocolate. How bad can it be?)

In the spinach plant, and in many other plants as well, the oxalate binds with the calcium to make crystals, effectively seizing the calcium for the plants’ own functions. These crystals are the salt-like particles I feel on the backs of the leaves. Nobody’s exactly sure what good the calcium-oxalate crystals do for the plant. After all, we don’t know everything. But one theory is that they deter chewing insects. 
Now you see them!

Even though, as I mentioned, our bodies always contain oxalates (our cells routinely convert Vitamin C to oxalates) this antinutrient has gotten a bad reputation in some circles. It is blamed for kidney stones, though this has not been proven. In one recent study of about 250,000 men and women the researchers concluded that “data do not support the contention that dietary oxalate is a major risk factor for incident kidney stones.”(1) Instead, other complex factors are at work, which I cannot pretend to understand. The Harvard Health letter recommends drinking plenty of fluids to keep mineral concentrations lower, eating calcium-rich foods to bind oxalates that might otherwise cause trouble, and avoiding calcium supplements. Calcium in food and calcium in pills apparently act differently, proving that we have a lot to learn about calcium and our bodies. And spinach, no doubt.

There is one more twist—if you’re still with me. Here is the plot so far: A green plant chemically holds back its calcium from animals for reasons of its own. We (humans, that is) would like the calcium to benefit our bones and teeth, and are a little leery of the plant’s materials and methods. We don’t trust oxalate. At all. We fear that it will cause us pain, and whether or not the plant is at fault is not all that important. The plant contains the antinutrient, the calcium robber.

So what do we do?

We take back the calcium!  
That’s right. Researchers are looking into genetically manipulating the oxalate levels in plants. Natural mutants that lack crystals, they say, grow just as well. And if we eliminate the oxalates, our teeth and bones will get the calcium.

Here is my message for those researchers:
I humbly submit that there’s a better idea. We should recognize that we’re not that smart. We should remember that we don’t know everything. Maybe, just maybe, spinach has a good reason for making calcium oxalate crystals. And, the truth is, we can have our spinach (and its vitamins A, B9, C, and K) and our calcium too if we just eat more kale, and carrots, and bok choy, and turnip greens. And drink more milk.   

And, by the way, don’t even think about messing with chocolate.

(1)Taylor, E., Curhan, G. 2007. Oxalate Intake and the Risk for Nephrolithiasis. JASN 18:7


  1. Thanks for these insights, Pam. I had heard about oxalates as a possible issue with wild greens but never thought about spinach. Nice writing!

    1. It wasn't until I began feeling the crystals that I began investigating them. Questions remain ... such as, how do the pre-formed crystals pass through the body? Are they different than those that are formed in the body? Sometimes the research doesn't quite satisfy. (We don't know everything)
      Thanks for your comment!

  2. A wonderful post Pam. The lab I worked in for graduate school often used spinach (the good ol' type with stems and grit) for experiments. I was new in the lab and the head scientist asked if I knew how to determine if the leaves were good for an experimental procedure. I expected a technical explanation to follow, when he took a handful from the pile and put them in his mouth and chewed away. With a big grin, he said you can tell from the crunch and taste!

    I never had fresh spinach growing up, but have been a big fan since that moment in my education. The taste and crunch and color can't be beat. And yes, the leaves are full of great health benefits for us as well.

    1. Thanks for your comment, Diane. I grew up in the era of frozen spinach also. No wonder Popeye had to convince us it was good to eat!

  3. Thanks for this post Pam. I just harvested some spinach that's been under a row cover all winter and started to grow again. I noticed it had a lot of crystals on the leaves though, and was wondering if it would be good to eat or if it will leave us with even more of that funny feeling on our teeth... it sounds like you are eating it anyway! It seems like maybe more stress equals more crystals....?

    1. I was not able to get the bottom of that question, Deb (good research project for a horticulture student). Calcium oxalate that forms in the kidneys can result in stones ... but there doesn't seem to be hard evidence that oxalate-containing foods are a big contributing factor. When already-formed crystals like those found on spinach leaves (which I've read are insoluble) are consumed, I suspect they are expelled. But, I have nothing to cite on that. I've eaten leaves with crystals (cooked because they're not the tender young leaves) and I live to tell about.

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  5. I know this post is older, but I wanted to say that I always wash my spinach in a mixture of cold water and apple cider vinegar. The crystals wash off easily, even when they might not with just plain water.

  6. Thanks, Anon. I guess that is the safe course of action, if you're prone to kidney stones.

  7. And drink your stinging nettle tea as it helps dissolve kidney stones :-D

  8. Fascinating - thanks for sharing!