Oxalic acid and oxalates are abundantly present in many plants, most notably rhubarb and sorrel. The root and leaves of rhubarb contain dangerously high concentrations of oxalic acid. Other foods that contain significant concentrations of oxalic acid include – in decreasing order – buckwheat, star fruit, parsley, poppy seed, rhubarb stalks, amaranth, spinach, chard, beets, cocoa, chocolate, most nuts, most berries, and beans.
In our body oxalic acid may also be synthesized via the metabolism of ascorbic acid (vitamin C), which is a serious health consideration for long term megadosers of vitamin C supplements. Read more