Oxalate is a compound commonly produced as a by-product of human metabolism. Unfortunately, once oxalate is produced, the human body can no longer efficiently break the molecule into other products. Therefore, in order to remove oxalate from the body, it must be filtered by the kidneys and excreted in the urine. Additionally, numerous foods have high oxalate content and this increased oxalate load must be filtered by the kidneys. This can lead to large amounts of urinary calcium oxalate crystals. For a patient with recurrent calcium oxalate stones, another dietary modification that may help prevent further stone formation would be to limit the level of dietary oxalate.
Foods high in oxalate content include the majority of green, leafy vegetables such as beet greens, rhubarb, spinach, and swiss chard. Also, preparations containing chocolate and cocoa have relatively high levels of oxalate. (click table to enlarge)