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Old 02-08-2011, 05:56 PM
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Hey guys,

I was reading about Oxalic Acid on the interwebz (albeit a cited article), and I was suprised to learn that it was potentially deadly, seems to be the cause of kidney stones, and is in many wild foragables, like rhubarb, mustard, spinach, watercress, dandelion, etcetera.

This article goes on to say that oxalic acid is detrimental to plants, too, but that the plants oxalic acid occurs in have an enzyme (protein) that breaks oxalic acid down, and, when you cook plants containing oxalic acid, it denatures the protein and causes your body to absorb the non-neutralized oxalic acid.

Granted, the danger of overdose seems distant, considering the article cites 11 pounds of rhubarb as a lethal dose, but, if a person were in a sustained foraging situation, the danger posed by oxalic acid seems like it would be more pertinent considering that oxalic acid-poisoning symptoms include fatigue, shock, vomitting, and many more.

So, to the questions:

1. Is this article accurate? Are certain cooked veggies higher in oxalic acid because the protein that usually neutralizes it within the plant is destroyed?

2. Does boiling constitute "cooking"? (It seems like it would)

3. Will eating raw uncooked vegetables (that are naturally high in oxalic acid) eliminate the danger of oxalic acid poisoning?

4. Cumulatively, am I warranted in worrying about the "dangers" of oxalic acid in a sustained foraging situation?

I appreciate any input anybody might have! Thanks!

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Old 02-09-2011, 11:30 AM
Chaosult Chaosult is offline
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As I understand it, oxalic acid in normal plant-sized doses is pretty readily excreted from the body unless you suffer from some kind of kidney problem.

The lethal dose of oxalic acid is something like 600 mg/kg, an amount you're very unlikely to intake, even in a survival situation.

Oxalic acid poisoning symptoms may occur at a much smaller dosage though. I can't seem to find any info on exactly how much oxalic acid one would need to ingest for symptoms to occur.
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Old 02-09-2011, 03:19 PM
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We have a lot of Japanese Knotweed which produces a lot of oxalic acid.
Old 03-27-2011, 04:49 PM
edibleplantguy edibleplantguy is offline
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Greetings twyggy and all,

Many plants contain oxalic acid as you correctly pointed out. As you also mentioned, it occurs in many well-loved and conventional vegetables as well (spinach, strawberries, rhubarb, and others). I certainly would not call oxalic acid deadly. You found someone posted a lethal dose of rhubarb would be 11 pounds/person. I don't know about you, but I would have a hard time ever eating 11 pounds of anything at a sitting. Oxalic acid is an organic acid (technically the simplest of the dicarboxylic acids) and they are related to fatty acids in their formation chemistry. They are but one of a class of materials often identified as oxalates. Oxalates come in two basic kinds: soluble, and insoluble. Oxalic acid is soluble and not dangerous in moderate quantities. However, there are other oxalates.

The biggest single problem for someone eating significant oxalic acid is that it binds to (and makes inaccessible to the body) your serum calcium. Calcium is an enormously important nutrient, not just to your bones and teeth. If you eat a diet high in oxalic acid, long term, your calcium levels will become insufficient to be healthy.

Here's the big thing. When calcium combines with oxalic acid it forms calcium oxalate which occurs in non-soluble crystals. These crystals come in two forms: botryoidal (solid round balls), and acicular (sharp penetrating needles). One reason to at least be aware of how much oxalic acid is in one's diet is because if you have a personal or family history of kidney stones you could be setting yourself up (especially if you aren't getting good quantities of water) for the botryoidal calcium oxalate crystals in your kidneys.

The acicular form is what makes your throat and tongue feel burning and itching when you stray into the Araceae (philodendron) family plants such as skunk cabbage or improperly prepared taro. Some inadequate edible plant books say one can eat these plants after simple boiling. But, not so. Remember, these crystals are insoluble; boiling is not the answer. The solution is usually high-temp roasting or long term drying (9 months plus).

So, if you are eating lots of plants in the rhubarb (buckwheat) family [Polygonaceae] be sure and track down some calcium supplements.

I hope this brings some clarity. Thanks for reading.

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Old 03-27-2011, 06:05 PM
lanahi lanahi is offline
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Spinach is high in oxalic acid. You would have to eat large amounts of it every day to be adversely affected by it, normally. Cooking and the use of dairy products with it neutralizes it.
Old 03-27-2011, 09:27 PM
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Unless your family has a history of calcium kidney stones it isn't really an issue at all. Lethal dose is around 2 pure ounces which translates into 10 to 30 pounds or more at one meal of various leafy vegetables. More so, as one doctor said, no one dies of such poisonings anymore. In my classes I simply say if you avoid spinach this is a plant you shoulg also avoid.


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