Well I am back in internet land! I wanted to bring up this topic because now is the time many people collect wild foods. Let me first point out this article is about soluble oxalates, not calcium oxalate crystals, found in skunk cabbage, jack in the pulpit - these are a real problem and I will discuss these in a future post. Once you start collecting wild foods you will inevitably run across this topic. You will hear statements ranging from "don't eat to much of those" to "You could die! Fear Fear!!!". In this post I will explain what oxalates are so you can make an informed decision when collecting wild foods.
What exactly are oxalates?
Oxalates or oxalic acids are naturally occuring and found in almost every thing that is living. They are water soluble as sodium oxalate or potassium oxalate salts. They are found in greater quanity in some plant families such as wood sorrel (oxalidaceae) buckweat (polygonaceae) and goosefoot family (chenopodiaceae).
Some of the specific plant that have higher concentrations are sorrels, rhubarb, spinach, wild spinach, docks, Japanese knotweed, black tea, & cocoa to name a few. High concentrations of oxalates are often accompanied by higher concentration of calcium.
Oxalates are a normal part of the diet and amino acid and asorbic acid metabolism.
Where the problem began.
The old literature such as the classic book Poisonous Plants of the United States and Canada by John Kingsbury warns against soluble oxalates. People tend to site this literature word spreads, an it becomes fact, oxalates are bad news. What should be considered is the book is a primarily a review of animal research, with these facts applied to humans. Even the author states in his book "Oxalate poisoning (even in animals) is fundamentally complex and poorly understood" This is my opinion, I am not a fan of animal studies. We (humans) are not cattle or sheep, in physiology or diet habits. Do you eat pounds of grass each and every day? Would you want to even if you had the time? Most of us have a very diverse diet. You can see where the focus on cattle and sheep for data on calcium deficiency in metabolism, comparing this to humans & there complex physiology and metabolism, there is a problem. As far as I know, there have been no verified cases of toxic intakes of the naturally occurring soluble oxalates in humans.
Most dietary oxalates are excreted in the feces. It is true that Oxalates can bind with calcium in the digestive tract making both the calcium and the oxalates unavailable for absorption. However, calcium and oxalate blocking or absorbtion is a complex metabolic process, to specifically say oxalates block all calcium absorbtion would be incorrect. The body is extreamly adaptive over time, and will find a way to absorb calcium to spite stomach contents.
Most documented poisoning can be attributed to rhubarb leaf consuption this is now attributed to anthroquinones, per once rhubarb has about the same amount of oxalates as spinach. In fact, the stalks have more oxalates than the leaves, (rhubarb crisp yummy!)
We convert excess vitamin C into oxalates that get filtered through the kidneys and come out in the urine. High intake of vitamin C results in greater oxalate production than any healthy consumption of vegetables high in oxalates.
If you have a abnormal physiological propensity for kidney stones, chronically undernourished in calcium, vitamin D and Phosphorus, or in the middle of a fast (hard on kidneys) I would watch my consumption of high oxalate foods.
Other than that you can see I think soluble oxalates are not a danger. Enjoy your wild foods!
Referance Wild Foods Adventurer Volume 6 number 3