By: Marina Biljak

Oxalates: do natural food items hide the danger of kidney stones?

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Today’s prevalent belief is that oxalates – harmless compounds found in many plants – can cause kidney stone formation.

Because of that, many nutritionists recommended avoidance of food items containing oxalates.

But is that really the truth?

Should we, because of the fear of kidney stone formation, avoid useful and nutritive food items such as spinach, parsley, raspberries and even cocoa?

What are oxalates?

Oxalates are natural compounds found in plants, animals and humans. From chemical aspect, they are placed in a group of organic acids.

Our body always contains a certain amount of them because our cells convert some other nutrients (such as vitamin C) into oxalates.

Oxalates can come into our bodies from the outside - from certain food items that contain various amounts of them.

Among fruits, vegetables and other food items the biggest oxalate sources are:

• blackberries
• blueberries
• raspberries 
• strawberries
• grapes
• fig
• spinach
• chard 
• parsley 
• leeks
• pulses
• almond
• cashews
• cocoa
• black and green tea

Of all plant parts, almost in all cases leaves contain the most oxalates, while roots and stems usually contain significantly lower amounts. 

Oxalates are mostly present in plant food items, while animal origin food items contain negligible amounts of these compounds.

It is assumed that oxalates in plants are used for removing excess calcium. But, according to some studies, plants also use oxalates for protection against infections and parasites.

Oxalates and kidney stones – a myth or a reality?

Oxalic acids have a potential to form strong bonds with various minerals such as potassium, sodium, magnesium and calcium. When that happens, compounds created in such manner are called salt oxalates. 

Salts of sodium and potassium oxalates are soluble in water and are ejected from our organism via our urine, but calcium oxalate is practically insoluble. 

That is why calcium oxalate, when there is enough of it in the body, has a tendency of forming crystals in kidney or inside the urinary tract. 

It is believed that this crystal can contribute to the formation of kidney stones that obstruct the functioning of kidney channel.

According to researches, as much as 80% of kidney stones found in adults were created by calcium oxalate. 

But there is no scientific confirmation that oxalate intake from our diet is to be blamed for kidney stone formation. 

Unfortunately, many nutritionists today recommend strict decrease of intake of the food containing oxalates as a form of preventing kidney stone formation.

Researches show that oxalate intake with people that already have kidney stones does not have any influence, since the stone was already formed. 

People that do not have kidney stone problems do not show any correlation of their health and oxalate intake, according to research.

Therefore, there is no need for limiting the intake of useful and healthy food items such as green tea, cocoa, spinach and grapes because of fear of kidney stone formation.

When you do need to limit oxalate intake

Despite the fact that the amounts of oxalates we intake are very small, there are several relatively rare health states that require a strict limitation of oxalate intake.

Such states include hypercalcemia (increased level of calcium in the blood) and primary hyperoxaluria (increased oxalate production in organism).

In such cases, oxalate intake should be limited to 50 mg a day.

But, how much is 50 mg of oxalates a day?

For example, one cup of raw spinach contains about 200 mg of oxalates. So, patients with such rare diagnosis are allowed only 1/4 of a cup of a spinach a day.

Oxalate content in 100 grams of raw food items:

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