Diversity of greens, cooking, and oxalic acid

Hey David, welcome to the Permies forum!

I've noticed that a lot of greens (both wild and cultivated, edible and not) tend to have different levels of oxalic acid, which contributes to kidney stone formation in the body and decreases calcium uptake in the body. Notably, spinach, Chenopodium spp., swiss chard, beet greens, sorrel, wood-sorrel, parsley, brassicas, and purslane. I LOVE my greens, and that list includes my favorites: spinach, kale, and beet greens. It has been suggested that oxalates in leaves and shoots may be a natural plant defense against herbivory.

Personally, I would like to eat a broad variety of greens, and growing your own to eat them would seem to fit well with that idea. Do you know of any cooking methods or ingredients that bind with oxalates and/or decrease it's uptake in digestion? With most greens, if we cook them do we love bioavailability of key nutrients? How do you maximize your nutrient uptake while minimizing your risk of giving birth to kidney stones?



Oxalis acetocella, eaten for millenia

sources:
wikipedia: Oxalic acid
Role of Calcium Oxalate Crystals in Plant Defense Against Insects
Oxalates in Biology Book
Paper on oxalic acid as a defense against chewing insects like aphids and leafhoppers

Yes, I agree, i was just looking at all the lush growth of the oca tops wishing I could eat them.

Caleb's questions occurred to me yesterday, as I harvested a row of Swiss chard after a hard freeze. Leafy things grow very well here. Most have oxalates. Half of my production are plants in the offending category.

Here's a good link on the subject: http://healthyonraw.com/should-we-eat-greens-high-in-oxalic-acid/
And a second source: http://www.drweil.com/drw/u/QAA400344/Avoid-Vegetables-with-Oxalic-Acid.html

My brother, who is studying to be a naturopath, says that you can eat some of it raw if you drink enough purified water. So, if you feel like eating a few bunches of high oxalate stuff, drink a lot of purified water for the next 24 hours. But, mostly cook them to convert/leach the oxalates and then get the bulk of your raw plant-chelated minerals from kale, mustard and brightly-colored roots.

Thanks for that info on blanching. Good to know. Dale, my climate on the other end of Canada has the same issue. Brassicas do pretty well here because it's colder. Luckily the article I linked to below says that oxalic acid concentration tends to be higher in young spinach plants and in plants in dry climates. At least that's not a problem here.

I've read elsewhere that consuming dairy or other foods rich in dietary calcium allows the oxalic compounds to bind with calcium and be excreted the unpainful way. The article claimed that eating rhubarb while drinking milk causes a gritty feeling in your mouth--which is supposed to be oxalic acid bonding with the calcium. Has anyone ever experienced this?


The same source also notes that oxalic acid may bond with iron in low doses. The article is great, though. I had no idea that we already have gut flora that can break it down for food.

A lot of interest in oxalic acid content of greens. A few thoughts on the subject Hope they are of some use. People on this forum already seem pretty well-informed on the subject.

Oxalic acid is a naturally occurring organic acid that is commonly made by plants, animals and humans. It is plentiful in many leaf crops and it has two negative impacts on our health. Oxalic acid combines easily with calcium, making calcium oxalate salts. The calcium in these salts is unavailable to us which lowers the total amount of available calcium in our diet. The second impact is also from calcium oxalate salts. If urine becomes overly saturated with these salts, some will precipitate out as crystals. This is akin to adding sugar to tea until it can hold no more, then watching sugar precipitate and settle at the bottom of the glass or pitcher. A small percentage @ of the population has a genetic anomaly that allows these tiny calcium oxalate crystals to form together into extremely painful kidney stones.

@ In the U.S. the proportion of people prone to kidney stones appears to have grown from under 4% in the 1970s to over 5% by the mid-1990s.

There is some controversy within the field of clinical nutrition over the actual risk from dietary oxalic acid. It is estimated that about 85% of the oxalate in our bodies is from metabolic by-products, and only 10–15% is consumed via food. Additionally, many researchers believe the actual loss of available calcium from dietary oxalate is relatively insignificant. And although about 73% of kidney stones formed by adults in the U.S. are calcium oxalate stones, many think that kidney stone formation is largely genetic and that it is not greatly affected by dietary oxalates either.

If you or any member of your family has had a kidney stone, it is reasonable to be very cautious about oxalate content of vegetables. Otherwise the benefit of the greens almost certainly outweighs the problems cause by the oxalic acid. The chart below gives a good picture of the oxalic acid content of many vegetables.

There are a few things that we can do, short of curtailing vegetable consumption, to reduce the impact of oxalic acid from greens. Getting enough calcium in our diets is the best protection against the loss of available calcium for bones and teeth. Unless your calcium intake is marginal or worse it is very unlikely that oxalic acid from foods will cause a deficiency.

As for kidney stones, the best, simplest and surely the cheapest protective measure is to drink more water. Water dilutes the urine and reduces the likelihood of calcium oxalate precipitating and forming painful crystals. Other beverages, especially coffee, wine and beer are also said to be protective perhaps because of polyphenols. Lemonade is especially effective because of the high levels of citrates, whereas heavy tea drinking seems to contribute to the formation of stones. Cooking generally doesn't have much effect on the oxalate content of foods. A decrease of 5–15% oxalate content is the most you are likely to see from cooking high-oxalate greens.
There are two other biological approaches to lowering the level of oxalates in our diet, both involving oxidase. This is an enzyme that quickly breaks down oxalic acid into harmless components. The first technique employs seedlings of rye, wheat or barley that are naturally rich in oxidase. The seedlings are dried at low temperature, ground, and added to foods high in oxalic acid. Tests have shown a 70% decline in oxalates in less than two hours of contact.
The second use of the enzyme oxidase takes place in the field. Over thirty years ago it was discovered that spinach leaves, one of the highest oxalic acid foods, also contain oxidase which could neutralize much of the oxalic acid. It was also discovered that nitrates deactivate this enzyme. Once again the most obvious course of action is to reduce the use of nitrate-based fertilizers, especially for growing greens.
If you want to remove all of the oxalic acid in the leaf crops that you eat, leaf concentrate is your best option. Essentially all of the soluble oxalic acid is washed out with the whey.

Some leaves, such as those of the taro plant, contain insoluble oxalate crystals called raphides. These don't combine easily with minerals and don't contribute to kidney stones or the loss of absorbable calcium. The needle-like raphides, however, can be extremely irritating to your tongue and throat, so it is imperative that taro leaves and those of related plants be cooked well (at least ten minutes) before eating.

Caleb asked, “With most greens, if we cook them do we lose bioavailability of key nutrients? How do you maximize your nutrient uptake while minimizing your risk of giving birth to kidney stones?”

In my opinion people often overestimate the loss of nutrients from cooking greens. Generally, the longer that the greens are cooked and the higher the temperature they are exposed to, the more significant the nutrient loss. Probably the most common loss of nutrients from cooking greens is the leaching of water soluble B vitamins and vitamin C from boiling. Temperatures above 350° F, such as those used in deep frying or baking, quickly damage beta-carotene. The high temperatures of pressure canning also destroys much of the beta-carotene. For example, canned grape leaves have only one-fifth the vitamin A activity of raw grape leaves.

However, quickly steaming or stir-frying often has the opposite effect, optimizing the vitamin A value in leafy vegetables by softening and rupturing cell walls. This makes almost all the nutrients in the leaf more available. Liquefying leaves in a household blender does an even better job of liberating beta-carotene from fibrous cell walls, effectively doubling the bioavailability of the vitamin A. Chewing accomplishes some of the same cell rupture, and thoroughly chewed greens provide more vitamin A than quickly gulped ones.

Certain foods eaten with greens will act to enhance or to inhibit the absorption of the nutrients in the greens. For instance, acidic foods and especially foods rich in ascorbic acid (vitamin C) eaten within an hour or so of the greens will enhance the absorption of iron, while drinking tea inhibits its absorption. A small amount of oil with greens improves conversion of beta-carotene in the greens to vitamin A.

As a general rule most greens should be eaten lightly cooked or raw if their texture makes this enjoyable. Some greens are too tough or harsh flavored for most people and require more cooking. And a few nutritious greens such as cassava, chaya, taioba, and taro require significant cooking to neutralize toxins or anti-nutritional substances.

Thanks for a very thorough and helpful answer, Dave. Very cool.

Dave Kennedy wrote:
Over thirty years ago it was discovered that spinach leaves, one of the highest oxalic acid foods, also contain oxidase which could neutralize much of the oxalic acid. It was also discovered that nitrates deactivate this enzyme. Once again the most obvious course of action is to reduce the use of nitrate-based fertilizers, especially for growing greens.

Chenopodium spp. concentrate nitrates in their leaves; does spinach do that too as an Amaranthaceae?

Dave Kennedy wrote:
Certain foods eaten with greens will act to enhance or to inhibit the absorption of the nutrients in the greens. For instance, acidic foods and especially foods rich in ascorbic acid (vitamin C) eaten within an hour or so of the greens will enhance the absorption of iron, while drinking tea inhibits its absorption. A small amount of oil with greens improves conversion of beta-carotene in the greens to vitamin A.

So homemade vinaigrette (with vinegar or citrus juice and oil) on greens might actually enhances the nutrition? That's fantastic.

Dave Kennedy wrote:
canned grape leaves have only one-fifth the vitamin A activity of raw grape leaves.

I've only ever eaten canned grape leaves. Do you harvest tender leaves in the spring and eat them as a salad green?

I eat them fairly regularly. They are more fibrous than most other leaves. I slice them very thinly and add them to salads, soups, and stews or casseroles. They are a traditional part of Middle Eastern cooking, in which typically, the newer leaves are wrapped around a mixture of say, rice and meat. Obviously, vegetarians could wrap rice and something else with grape leaves. I believe they are normally steamed in this process. Grape leaves have a light, tart flavor. I have also put them in my sauerkraut. I still slice them thinly (chiffonade) when I put them into sauerkraut. They are also put into sauerkraut to keep the vegetables crisp.
JohN S
PDX OR

I'm glad to hear that oil helps us absorb beta carotene. My vegetables are a handy butter delivery system.

Waou Dave, you are realy giving pricise and usefull tips, thanks!

Dave Kennedy wrote:There are two other biological approaches to lowering the level of oxalates in our diet, both involving oxidase. This is an enzyme that quickly breaks down oxalic acid into harmless components. The first technique employs seedlings of rye, wheat or barley that are naturally rich in oxidase. The seedlings are dried at low temperature, ground, and added to foods high in oxalic acid. Tests have shown a 70% decline in oxalates in less than two hours of contact.

Ooch, not good for gluten free diet!

The second use of the enzyme oxidase takes place in the field. Over thirty years ago it was discovered that spinach leaves, one of the highest oxalic acid foods, also contain oxidase which could neutralize much of the oxalic acid. It was also discovered that nitrates deactivate this enzyme. Once again the most obvious course of action is to reduce the use of nitrate-based fertilizers, especially for growing greens.

Nitrogen is what is making big green leaves... so what? Get little leaves in poor ground? Do we really have to do this?

Some leaves, such as those of the taro plant, contain insoluble oxalate crystals called raphides. These don't combine easily with minerals and don't contribute to kidney stones or the loss of absorbable calcium. The needle-like raphides, however, can be extremely irritating to your tongue and throat, so it is imperative that taro leaves and those of related plants be cooked well (at least ten minutes) before eating.

I also have Chaya that you mention, and cassava.
Cooking time is really an issue because I have never found the same information.
Can it be checked with tasting?
I mean if there is some picking of the mouth, then it is not enough....
Whenn you say "at least"... what would be ideal?
...I had in mind something like 30mns

And... do we have to get rid of the cooking water?
Or is it just the cooking that is needed?

Thanks, these are very important informations I was lacking!

If you want to remove all of the oxalic acid in the leaf crops that you eat, leaf concentrate is your best option. Essentially all of the soluble oxalic acid is washed out with the whey.

Sorry, I do not understand.

Is the leaf concentrate, what you told us about germinated cereals?

Did I miss something about whey? It has nothing to do with leaves, so what is it?
How do you use whey for this purpose?

OK! I edit because you refer to what I have seen in the website leaves for life, and the technic of the leaf concentrate, some drying of the extract5ed juice if I understand my 1st quick reading.

It's quite common, here where I live, to have a bottle of calcium chloride solution (calcium chloride, water and lactic acid) in the cupboard to add to spinach and rhubarb dishes. One uses 2 tsp. per kilo, either while cooking or afterwards, in order to neutralize the oxalic acid. I don't remember something like that being generally available when I lived in the US, but it might be worth checking. It doesn't seem to be used for raw greens, however. I don't know if it would have the same effect without heat.

Xisca Nicolas wrote:

The second use of the enzyme oxidase takes place in the field. Over thirty years ago it was discovered that spinach leaves, one of the highest oxalic acid foods, also contain oxidase which could neutralize much of the oxalic acid. It was also discovered that nitrates deactivate this enzyme. Once again the most obvious course of action is to reduce the use of nitrate-based fertilizers, especially for growing greens.

Nitrogen is what is making big green leaves... so what? Get little leaves in poor ground? Do we really have to do this?

I watched a video recently by Graeme Sait, a guy from the Australian permaculture scene, and he mentions that not all nitrogen is created equal. He claims in the video below (which is super info dense) at around minute 7 that current agricultural practices with nitrate ( NO3−) fertilizer means that our food crops contain 75% nitrate and only 25% (roughly) ammonium nitrogen (NH4+), when the natural balance should be the opposite. I've started another thread here that discusses N sources more.

I'd be interested to know, from Dave or someone else, whether NH4+ or NH3 have the same effect on the oxidase.

This could be important for us as designers because the Frankia bacteria in leguminous root nodules produce NH3, and our animal (and human) N inputs from urea are NH4+.

Graeme Sait's video (comments on N-balance of food and toxicity at around 7:00):

"When grown with soluble nitrogen fertilizer, amaranths can accumulate dangerous levels of nitrates in their leaves. This problem is worse during dry weather or when the plants are grown in a greenhouse. Nitrates are especially a problem for babies and young children. "

Caleb Worner wrote:current agricultural practices with nitrate ( NO3−) fertilizer ...

This could be important for us as designers because the Frankia bacteria in leguminous root nodules produce NH3, and our animal (and human) N inputs from urea are NH4+.

Seems the problem linked to N when with O? And not with H...

so depending on what goes into sauerkraut it could be higher or lower in oxalates... does the lactic acid in it help to lower oxalates?