The Dark Side of Leafy Greens

By The Bone Babe Jan 20, 2025

For some of us, spinach may conjure an image of Popeye, the spinach-loving Sailor with bulging muscles who scarfed cans of the green stuff and sang, “I’m strong to the finich, ‘cause I eat me spinach.” But did that spinach really make him strong? 

We are told by nutrition experts and health enthusiasts on IG and Tik Tok to “eat your leafy greens,” but before ordering your next raw kale salad, there are a few things you need to know when it comes to leafy greens and bone health.

Is that what that is?

Certain foods contain a compound called oxalic acid (aka oxalates) which are considered an anti-nutrient. Sounds bad, right?  Well, it can be. An anti-nutrient is basically a plant’s survival mechanism; it’s the plant’s way of saying, “hey, don’t eat me!” Oxalates bind to certain minerals in the foods you eat, such as calcium and magnesium, and can prevent the body from absorbing and utilizing them. You know that weird feeling you get in your mouth when you eat spinach or Swiss chard, like you’ve swabbed your teeth with chalk, yep, that’s oxalic acid! 

Spinach, beet greens, chard & collards are all examples of high-oxalate greens. Although some of them contain high levels of calcium and magnesium, because these minerals bind to oxalic acid, it makes them less bioavailable, meaning, less able to be absorbed. Spinach, chard and beet greens have higher amounts of oxalic acid, while kale is on the lower end of the spectrum.

So why is this a problem? 

Oxalic acid binds with calcium, magnesium and iron in order to be excreted by the body. Calcium and magnesium are key minerals vital for bone health, among other bodily functions. Our depleted soils and SAD diets already make us deficient in these minerals so eating foods that can further deplete them is a problem, particularly for those of us with compromised bone health.

If you are someone with an impaired digestive system, whether it’s from frequent antibiotic usage, celiac disease, gluten sensitivity, taking NSAID’s or antacids, you may be even more susceptible to oxalates. 

So, do I have to stop eating greens?

Some studies suggest that it is the calcium to oxalate ratio that matters. Thus, if you consume enough daily calcium, the oxalates will not block its absorption. But the studies do not seem to be conclusive and, how many of us, especially post-menopausal women, are really getting enough calcium daily? 

But before you ditch your darling greens, there is a way you can reduce their oxalate content and make the calcium and other minerals they contain more bioavailable. Give them a bath! 

Cooking methods and hacks

In a study that looked at the effect of cooking methods on the oxalate content of various foods, blanching leafy greens for 10 minutes produced the best results in terms of reducing their oxalate content. For those who like to geek-out on the why, the anti-nutrient content is highest on the superficial layer of the vegetables and blanching ruptures this layer. Pressure cooking for 15 minutes came in second, but, have you ever seen what spinach looks like after 15 minutes in a pressure cooker?! 

To reduce the oxalate content in your greens yet still have them resemble something that used to grow upright in the ground, I’d stick with steaming, boiling, or blanching them. Drain them thoroughly and perhaps give them a little rinse, and don’t save the cooking water as all the oxalic acid that has leached from your greens is floating around in there. 

If you want to add them to soup or stews, remember, if you add them in raw, the oxalic acid will leach into the broth, so precook as per the above instructions before adding them. And no more raw spinach or kale in your smoothie. You can steam them, squeeze them, freeze them (say that fast 3 times) so they’ll be ready when you need them.

Mix it up!

You can also enjoy a number of leafy greens which do not have a high oxalate content, including: arugula, dandelion greens, mizuna, mache (lamb’s lettuce,) nettles, turnip greens and romaine as well as other lettuces. 

How much calcium is really in there? 

Many health Influencers love to sing the praises of spinach, in particular, for its high calcium content. So how much calcium does it actually contain? Spinach has about 115 mg of calcium per half cup cooked, but because of its oxalic acid content, you would need to eat about 16 cups of raw spinach or 8 cups cooked to get the same amount of calcium contained in one cup of yogurt because the oxalic acid in the spinach means the calcium it contains is not bioavailable. So, the next time your friend tells you she’s getting plenty of calcium from her diet while daintily picking at her spinach and roasted beet (also high in oxalates) side salad, you might ask her if she’s planning to order 8 more! 

Traditional wisdom

According to Dr. Josh Axe, Doctor of Natural Medicine & Clinical Nutritionist, pairing oxalate foods with calcium-rich foods, could help with excreting oxalates out of the body. So the good news is, there is a raison-d’etre for that delicious Southern specialty, creamed spinach. Or add some fresh goat cheese to that aforementioned spinach salad. 

Like many issues around nutrition, there are conflicting opinions on whether or not oxalates are problematic but I’m not willing to potentially risk my bone health, are you? So although you may have to give up your beloved raw spinach salad or raw kale smoothie, steaming your greens, or choosing from the many delicious varieties with low oxalate content is a small compromise to allow you to have your greens and eat them too! 

As always,

 Bone Santé