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The available information on oxalic acid is confusing and varies with every source. According to one source our regular breakfast (oatmeal, dried figs, blueberries, wheat germ, flaxseed, and soy milk), our favorite dinner vegetables (spinach, beets, okra, and beans), and our regular snacks (almonds, peanuts, and berries) ALL contain high levels of oxalic acid.
Aside from the danger of getting kidney stones, most sources are undecided about the effect of high levels of Oxalate in one's diet. Some say that it prevents absorption of calcium, iron, and other minerals but the extent of this problem is uncertain. Should we be concerned?
For most folks high oxalic foods are not an issue. There are some people who are prone to calcium oxalate kidney stones and there's a feeling that limiting foods high in oxalate might help with treatment. The general recommendation for those people is no more than 50 mg of oxalic acid per day.
There is not a lot of available information about oxalate content because the USDA has not measured this as extensively as other nutrients. Here's a reliable source of information on the oxalate content of foods, from the Children's Hospital of Dayton: Oxalate Content of Foods.
Thanks for writing,
Timothy S. Harlan, MD, FACP