Oxalic Acid in Vegetables

Although there seems to be consensus on the fact that many vegetables contain oxalic acid, and that too much of this chemical may be bad for you, opinions seem to wildly diverge after that point. Oxalic acid (or oxalates) give some plants, such as rhubarb and sorrel, their sour flavour, but they can also severely irritate the tongue and throat. There is also some speculation that they contribute to the formation of kidney stones, and they are thought to inhibit the absorption of calcium. 

Despite all these things warnings, plants containing oxalic acid are still edible. Oxalates probably inhibit the absorption of calcium found in the same food, but not in other foods eaten at the same time. Cooking will decrease the amount of oxalates in a food (it goes into the cooking water). Some plants that are probably somewhat high in oxalic acid are amaranth, chives, lambsquarters, parsley, purslane, rhubarb and spinach, and possibly beet greens and swiss chard.

So what about rhubarb leaves, which contain high oxalic acid, and have caused reported deaths when eaten, even cooked? They apparently also contain anthraquinone glycosides, which alone, or together with the oxalates, are what likely causes the poisoning. So go ahead and eat plants containing oxalic acid, but if you worry about these things, don't eat five pounds, raw, in a single sitting.

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