Journal of Evolution

Journal of Evolution

World-wide, our contemporary health crisis involves the popularity of foods that
cause both toxicity and nutrient deficiencies. Usually we think of sugar, trans-fats,
and artificial ingredients as central culprits. Yet, one of the most potent toxins that
people regularly ingest is naturally occurring oxalic acid and its oxalate salts. In the
body, food-borne oxalates not only generate direct toxicity, they also deplete
nutrients. This commentary argues for increased awareness of oxalates in foods and
cautions against promotion of and regular use of foods high in oxalate.

Toxic Mechanical Injury Due to Calcium Oxalate Crystals in Plants
The insoluble calcium oxalate crystals in plants come in a wide array of sizes and
shapes, including bundles of double pointed needles called raphides18. These
calcium oxalate crystals are relatively stable minerals serving as durable
microfossils of some archaeological interest, being found where other plant
residues are no longer evident19.
Raphides are known to cause skin irritation, and oral and upper respiratory
injury20. The non-food plant, Dieffenbachia, is a long-recognized and dramatic
example. Excellent photographic illustration of oral and upper respiratory damage
is offered in a recent report of a poisoning case requiring a 9-day hospitalization
due to injuries sustained from brief exposure to a drop of Dieffenbachia sap21.
Dieffenbachia possesses a system described as a defensive ‘microscopic blowgun’
whereby the tightly bundled raphides are forcefully ejected (assisted by turgor
pressure of cell contents) for a distance of two to three cell lengths when the cells
are disrupted. The “Needle Effect” of raphides has been demonstrated countless
times, whereby traumatic injury results from the release of the raphides combined
with the effects of proteases, soluble oxalate, and other chemical toxins carried on
their surfaces and in their grooves in a defensive synergism22.
In many plants, including many that we eat, calcium oxalate crystals are
present, although there is limited research on the specific forms and quantities of
these crystals in foods. Hard and sharp-edged, oxalate crystals take many forms, in
varying sizes, beyond the raphide23–26. They have the potential to inflict mechanical
injury to skin20, teeth27, and the mucosal linings of the alimentary canal28. These
crystals may play an unrecognized role in the etiology of gut-associated illness.
This type of localized oxalate toxicity involves mechanical abrasion and does not
depend on absorption into the body.

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