Before you sign off on the green veg adventure, consider that things may not be as they seem as the supposedly naughty Oxalic Acid occurs more generally than just in spinaches.
Nonetheless, there are still plenty of green leafy things out there to tempt you if you seek to isolate your kidneys.
The Leaf for Life project has some preparation suggestions here: LINK.
Taken from the document 21st Century Greens. A must read.
You gotta read their resources as they make for a great green veg bible --such that the info can be life changing -- at least lifestyle changing..
As LfL points out:
Oxalic acid is a naturally occurring organic acid that is commonly made by plants, animals, and humans. It is plen-tiful 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.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. About 75% of kidney stones formed by adults in the U.S. are calcium oxalate stones. However, many experts think that kidney stone formation is largely genetic and that it is not greatly affected by dietary oxalates.If you or any member of your family has had a kidney stone, it is reasonable to be very cautious about oxalate content of vege-tables. Otherwise the benefit of the greens almost certainly outweighs the problems cause by the oxalic acid....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 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 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. Recently, it has been discovered that the intense irritation is actually due to the effect of the sharp raphides puncturing the tissues of the mouth and throat, combined with proteases (enzymes that break down proteins) attacking the punctured tissues
Access individual PDF files from the list below:
Here is an old but comprehensive list of oxalates in food...
As an aside -- a supplementation -- seaweeds are also green and leafy. With some bonuses. See here.
They may register low on the oxalate spectrum but they also tick really high with calcium.
I'm sure seaweeds' content will vary depending on the bay or ocean they were harvested from -- but here's an indicative break down:
The point that strikes me is that if you combine seaweed with green leafy terrestrial plants, you -- like the Japanese and Koreans -- you maybe onto something. -- umami aside.