Oxalates are among the best-known antinutrients in foods, along with lectins, gluten, and phytic acid. When oxalic acid binds to calcium, crystals form that cause kidney stones.
Many people do not know that plant foods have risks and side effects.
In this article, you will learn about the dangers of high oxalate foods and how to reduce them with simple methods and an appropriate diet.
What Are Oxalates?
Oxalic acid and oxalates (its salts) occur as end products of metabolism in various plant tissues.
When oxalic acid is bound to sodium, potassium, calcium, or ammonium ions, it is called an oxalate. In this form, oxalic acid is most commonly found in foods.
When consumed, these plants can be detrimental because oxalates bind calcium and other minerals. They can significantly limit calcium intake in vegetarians.
Calcium oxalate is a poorly soluble salt that is slowly excreted.
In ordinary people, about half of the oxalic acid in urine comes from food, and the other half is from the body’s synthesis.
The properties of this antinutrient can lead to problems beyond nutrient deficiency.
Excessive consumption of foods high in oxalic acid leads to calcium oxalate stones in the urinary tract when the acid is excreted in the urine (Noonan et al. 1999).
Side Effects of Oxalates
When oxalates bind to calcium, they can form calcium oxalate crystals. Oxalate crystals prevent the body from absorbing nutrients, such as calcium and iron.
Oxalic acid can bind the following minerals and metals and form a corresponding oxalate:
Because they inhibit nutrient uptake, oxalic acid and oxalates are called antinutrients.
They are natural toxins that protect plants from predators. Oxalate crystals can hurt insects like tiny razor blades, so they often give plants high in oxalates a wide berth.
Calcium oxalate crystals can cause muscle pain, osteomalacia, and human rickets. If they get into the kidneys, they can cause kidney stones.
If there is too much oxalic acid in the body, it is more likely to bind to calcium and form kidney stones. About one in ten people have a kidney stone at least once.
Foods that contain a lot of vitamin C can increase oxalic acid in the body. Few people know that the body converts about 60 mg of vitamin C into oxalates daily (Knight et al. 2016).
Over 1000 mg of vitamin C daily increases the risk of kidney stones by about 40% (Taylor et al. 2004).
Gut bacteria have the task of breaking down oxalates.
However, taking antibiotics can cause these good bacteria in the gut to be reduced. The result is an accumulation of oxalates and an increased risk of kidney stones (Nazzal et al. 2021).
Symptoms of High Oxalates
When there is too much oxalic acid in the body or oxalates in the urine, it is called hyperoxaluria. A distinction is made between primary and secondary hyperoxaluria.
Primary hyperoxaluria is an inherited metabolic disorder. In contrast, secondary hyperoxaluria is an increased intake of oxalates through food or a change in the intestinal microflora, as described above.
The classic sign of hyperoxaluria is a kidney stone.
However, excessive oxalate can manifest itself in different ways. In people with leaky gut, oxalates can cause complications in places of the body where they are not suspected.
Possible symptoms of too many oxalates in the body include:
- Grainy stools
- Frequent urination
- Pain when urinating
- Low urine output
- Blood in the urine
- Back and abdominal pain
- Pain in the bones
- Swollen joints
- Mottled skin
- Gum inflammation
- Poor circulation
- Chills or fever
- Stomach upset or vomiting
When the kidneys can no longer excrete the amounts of calcium oxalate, the crystals begin to be deposited in various organ systems. Possible consequences are recurrent kidney stones, urinary tract infections, and chronic kidney disease (Shah et al. 2022).
Due to their toxic effects, 4 to 15 g of oxalates can be fatal (Noonan et al. 1999).
What Foods Are High in Oxalates?
Grains, legumes, vegetables, fruits, nuts, and seeds can be rich in oxalic acid (Bargagli et al. 2020).
In principle, small amounts of oxalates are found in all plant foods. Thus, avoiding them is impossible, but limiting the intake of foods particularly rich in oxalic acid is possible.
Here is a detailed list of foods high in oxalates:
- Black Tea
- Instant Coffee
- Cocoa products and drinks
- Soy products and drinks
- Brazil nuts
- Pine nuts
- Chia seeds
- Sesame seeds
- Almond Butter
- Peanut Butter
- Lemon, orange, lime peel
- Wheat bran
- Wheat germ
- Whole wheat
- Sweet potatoes
- Summer squash
- Swiss chard
- Black pepper
Foods that contain a lot of oxalates often look more nutritious on paper than they are. Spinach, for example, is a very calcium-rich food.
However, because spinach is also a high oxalic acid food, the body can absorb almost none of the calcium (Noonan et al. 1999).
Although it is difficult to set a limit, most healthcare providers recommend no more than 50 mg of oxalates per day in the diet.
Therefore, reducing the foods listed above that are high in oxalic acid makes sense.
For example, 100 g of raw spinach can have an oxalate content of 330 to 992 mg (Borgren et al. 2003).
Therefore, half a kilogram of raw spinach could already be fatal for some people. Fortunately, there are methods to reduce oxalic acid in foods.
How to Reduce Oxalates in Food
According to studies, there are several ways to reduce oxalic acid in foods (Noonan et al. 1999):
- Soaking: Leaching in water can reduce oxalate levels in foods. This method alone is not among the most effective. However, soaking could reduce oxalic acid in yam tubers by 40-50% combined with cooking.
- Steaming: In contrast, subsequent steaming of yams could only reduce oxalates by 20-25%.
- Baking: Baking depleted yams in the tube was even less effective. It could reduce oxalic acid in the food by 12-15%.
- Cooking: Although cooking is most effective for reducing oxalic acid, it simultaneously removes water-soluble minerals from the food. Boiling is particularly effective for legumes (Akhtar et al. 2011).
- Roasting: Roasting is the least effective method. Roasting chicory roots increased their oxalate content.
- Sprouting: soaking and sprouting can lower oxalic acid in soybeans. Additional cooking can further lower oxalate levels. However, soaking and cooking are not as effective as sprouting.
- Hulling: In horse beans, hulling is highly effective. It reduced the oxalate content in the seeds by 38%.
The crux of reducing oxalates in foods is that almost any effective method also loses nutrients.
Hulling is the exception in this regard. On the one hand, it is very effective; on the other hand, there are even more antinutrients, such as lectins, in the peel. Finally, the shell has the task of protecting seeds from predators.
However, you cannot hull all foods high in oxalates. Spinach is an excellent example.
Avoiding high-oxalate foods is the most effective way to minimize the risks of oxalic acid and prevent kidney stones.
Low oxalate diets are also used to treat vulvodynia, which causes chronic pain in the female abdomen (Konstantynowicz et al. 2012).
In addition, there is evidence that reducing oxalic acid in the diet may prevent autism. Autistic individuals have significantly higher levels of oxalic acid in their blood (Sadownik 2014).
Consequently, it may be healthy to limit dietary oxalate intake for various reasons. Here is a list of foods that contain minimal oxalates:
- Passion fruit
- Egg noodles
- White rice
- Dijon mustard
The Bottom Line
The focus on marketing the benefits of plant foods is so high that people forget about possible risks and side effects.
Oxalic acid and its salts are part of plants’ natural pest defenses. Oxalate crystals can also cause harm to the human body in excessive amounts. The most common example of this is kidney stones.
While some sources also recommend increased calcium consumption as a strategy against kidney stones, I am highly skeptical (Ferraro et al. 2020).
Finally, oxalic acid binds to calcium. The results are oxalate crystals, which are the origin of kidney stones. Therefore, whether the combination of foods with many oxalic acids and calcium is advisable may be doubted.
In many nutritional problems, an excess of one substance cannot compensate for the overconsumption of the other, even if many people wish it could.
Those who suffer from gastric, inflammatory bowel disease, or autoimmune disorders and want to eliminate oxalates should look at my Carnivore Diet Plan.
Frequently Asked Questions (FAQ)
What foods neutralize oxalates?
Peeling, sprouting, soaking, cooking, steaming, and baking can neutralize food oxalates.
What are the highest oxalate foods to avoid?
Spinach, rhubarb, buckwheat, rice bran, and almonds contain very high amounts of oxalates.
How do you flush oxalates out of your body?
To get rid of oxalates in your body, follow a low-oxalate diet and hydrate properly.
Mag. Stephan Lederer, MSc. is an author and blogger from Austria who writes in-depth content about health and nutrition. His book series on Interval Fasting landed #1 on the bestseller list in the German Amazon marketplace in 15 categories.
Stephan is a true man of science, having earned multiple diplomas and master's degrees in various fields. He has made it his mission to bridge the gap between conventional wisdom and scientific knowledge. He precisely reviews the content and sources of this blog for currency and accuracy.
Click on the links above to visit his author and about me pages.