In many plants, oxalate crystals are present. These relatively large microcrystals have the potential to inflict mechanical injury. On the other hand, ionic, soluble, and nano-crystal forms of oxalate are readily absorbed. Bioaccumulation in humans is well documented. Crystals and ionic oxalate are associated with pain and both functional and chronic disorders.
Today’s many health challenges have led people to select foods purported to be healthier, many of which are high in oxalate. Modern dietary approaches have placed great emphasis on the health benefits of vegetables, nuts, and spices. Many of these are high oxalate foods that are now distributed through a global food system in which seasons have been erased, making harm from dietary oxalate more likely now than ever before. Lack of awareness of this potential creates fertile ground for continued increases in human suffering and public health problems.
Norton, Sally K.
"Lost Seasonality and Overconsumption of Plants: Risking Oxalate Toxicity,"
Journal of Evolution and Health:
3, Article 4.