Should You Worry About Oxalates?

You might have heard that you need to reduce your intake of oxalates, and that eating too much causes kidney stones, vaginal pain, autism, and more. 

But is there any truth to these worrying claims, and what are oxalates anyway? Here, we investigate.

Oxalates: What and where are they?

Oxalates — also called oxalic acid — naturally occur in plants and are classed as an antinutrient.

Antinutrients compete with your body’s ability to absorb the nutrients in food. That sounds bad, but don’t worry, we’ll come back to it.

Here are some of the plants that contain particularly high levels of oxalates:

This list provides two important insights:

So, what sparked the health concerns and is there any evidence?

Antinutrient abilities

Oxalates are called antinutrients because they bind to minerals, including sodium, potassium, and calcium, and prevent your body from absorbing them. 

It’s true that consuming too much oxalates can be fatal. In fact, we’ve known about its toxicity since the early 19th Century.

Researchers have estimated that it would take 0.77 ounces (22 grams) of oxalic acid to kill you. 

If you’re eating a well-rounded diet, including adequate vitamins and minerals, oxalates won’t be a problem for most people. Because they occur in many plants that contain a wide range of nutrients, the benefits far outweigh the dangers of consuming them.

Now, let’s look at the specific claims surrounding the role of oxalates in kidney stones, vaginal pain, and autism.

Kidney stones

The majority of kidney stones contain calcium oxalate, which is calcium bound to oxalate. Research shows that people who have more oxalate in their urine are at an increased risk of developing kidney stones.

So, concerns about oxalate intake and its links to kidney stones are understandable.

Similarly, another study showed that one of the major dietary risk factors for kidney stones is a lack of calcium. So, what’s going on?

Paradoxically, it seems that oxalate’s antinutrient activity may actually help prevent kidney stone formation: When calcium binds to oxalates in the gut, it prevents either of them from being absorbed into your blood. 

And if they can’t get into your blood, they can’t reach your kidneys to create a stone — they exit in your poop. As we mentioned, higher oxalate levels in urine are linked to kidney stone risk. But if you eat enough calcium, oxalate binds to it and it leaves in your stool instead.

So, rather than cutting out oxalates, simply upping calcium intake may mitigate this increased risk.

Dairy products, soy, nuts, seeds, and calcium-set tofu are great sources of calcium.

Interestingly, some plants that are high in oxalates are also rich in calcium, like broccoli, beans, and Brussels sprouts, making them inherently balanced to help support your health and reduce your risk of kidney stones.

Oxalates and gut bacteria

Before we move on from kidney stones, there’s another factor that makes this relationship more complex.

Certain gut bacteria, like Oxalobacter formigenes, which are present in 60-80% of adults, can break down oxalates. 

So, if your gut microbiome contains a thriving population of O. formigenes, eating oxalates is even less likely to be a problem.

Importantly, if you are at increased risk of kidney stones or have another medical condition, your doctor may suggest you try a low-oxalate diet. And you should follow their advice. But for most people, this isn’t a huge concern. 

Scientists are still debating how useful a low-oxalate diet is for people with kidney stones, as the titles of these two scientific papers from 2021 demonstrate:

Oxalates and vaginal pain

Unlike the links between oxalates and kidney stones, which required a deep dive into the science, rejecting the links to vaginal pain is much easier.

This claim appears to come from a paper published in 1997 on urinary oxalate excretion and its role in vulvar pain syndrome — a condition marked by burning, pain, or discomfort in the vulva.

The researchers recruited 130 people with vulvar pain syndrome and 23 without. Of the people with vulvar pain syndrome, 59 had high levels of oxalates in their urine. When they treated these women to reduce oxalates, around one-quarter of them reported improvements in symptoms.

Indeed, the authors write that oxalates are unlikely to cause the condition, but they might make it worse.

A study in 2008 revisited this relationship. The researchers recruited 242 people with vulvar pain syndrome and 242 controls, concluding that “dietary oxalate consumption does not appear to be associated with an elevated risk of [vulvar pain syndrome].”

Oxalates and autism

The theoretical link between autism and oxalates is relatively new. A study from 2012 was particularly influential. 

This research involved 36 children and adolescents with autistic spectrum disorder (ASD) and 60 control participants without ASD, matched for age, sex, and various body measurements.

Although this is a surprising result, it doesn’t show that autism is caused by elevated oxalate levels. And there’s currently no evidence at all to suggest that oxalates cause autism.

It’s also important to mention that the 2012 study hasn’t been replicated, so it may not hold true when scientists look at larger groups.

However, some experts do think that a subset of people with ASD may have dysfunctional oxalate metabolism.

Consequently, some suggest trying a low-oxalate diet to see if it helps, although there seems to be little evidence that this approach works, aside from one survey:

In 2009, the Autism Research Institute published data from a survey of over 27,000 parents of children with ASD. The survey asked them about medications and other interventions they had tried, including a low-oxalate diet.

This implies that some may find it beneficial, but this was a survey rather than a scientific study. Parents only rated behavior changes using a 6-point scale, and we have no information about which symptoms were influenced and whether the improvements lasted. 

So, whether the diet works or not, no experts are suggesting that dietary oxalates increase the risk of autism. Rather, certain people with ASD may have problems with oxalate metabolism and might benefit from reducing their intake. 

As it stands, the evidence in support of a low-oxalate diet for ASD is virtually non-existent.

Who should avoid oxalates?

Oxalates consumed in plants are safe for the vast majority of people. However, doctors may advise some people to reduce their intake. That includes people with:

• A family history of kidney stones.

• Certain bowel conditions, like short bowel syndrome and inflammatory bowel disease (IBD): These conditions increase the risk of kidney stones.

• Primary hyperoxaluria: Rare genetic disorders that cause a buildup of oxalates in the kidneys. 

• Weight-loss surgery: This can increase the rate of kidney stone growth.

What should you do?

Beyond the conditions mentioned above, consuming oxalates as part of a well-balanced diet doesn’t seem to be in any way dangerous. 

The current media attention that oxalates are receiving is misplaced. For the vast majority of us, consuming plants containing oxalates is entirely safe and will actually support your long-term health.