Should You Avoid Oxalic Acid?

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Recently, we encountered a suspicious claim: that cruciferous vegetables (like kale, broccoli and radishes), spinach, nuts and many other healthy foods should be avoided because they contain oxalate/oxalic acid. The reason given was that oxalic acid forms calcium oxalate crystals throughout the body, leading to kidney stones, muscle pain, arthritis and various other problems. While oxalic acid is involved in kidney stone formation, the idea that you should avoid healthy foods that contain it is bad health advice. Let’s take a look at the science and dispel any myth surrounding these foods.

What Is Oxalic Acid?

Oxalic acid is a naturally occurring acid found in many foods. Unlike amino acids and fatty acids, oxalic acid cannot be used by the body for energy, meaning that most of the oxalic acid that is absorbed into the blood will be excreted in the urine alongside other waste. If the urine contains too much oxalic acid dissolved in too little water, oxalic acid can bind to calcium to form solid calcium oxalate crystals, which are the most common form of kidney stone.

Oxalic acid is also described as an ‘antinutrient’, because it binds to minerals like calcium and iron in the gut to form calcium or iron oxalate crystals, which can’t be absorbed.

Why You Shouldn’t Cut Out Foods Containing Oxalic Acid

Oxalic acid doesn’t sound so great, so why not cut out all foods containing it? Simply put, the downsides of consuming oxalic acid are slimmer than you might think, are easily mitigated by other practices and are outweighed by the health benefits of the foods that contain them.

Most foods containing oxalic acid are very healthy, so avoiding them because they might slightly harm your mineral absorption isn’t worth it – it’s much more important to have a balanced and diverse diet. Cutting out oxalic acid also won’t eliminate the risk of kidney stones, because 50% of the oxalic acid in the urine is actually produced in the body as a result of amino acid and vitamin C metabolism. Even people with kidney stones are not always advised to restrict oxalic acid consumption. Oxalic acid may make kidney stones more likely, but proper hydration is still the key to avoiding kidney stones, and there are also other methods listed below that can effectively limit the potential harm done by oxalic acid.

How To Mitigate The Effects Of Oxalic Acid

• Drink more water: As already mentioned, calcium oxalate crystals form when the urine contains too much oxalic acid and not enough water. Drinking more water will help prevent these crystals from forming, and will help small crystals to be passed in the urine before they have a chance to become large crystals.
• Consume foods high in calcium alongside oxalic acid-containing foods: This might sound counter-intuitive, since calcium is what oxalic acid binds to to form calcium oxalate crystals. However, consuming calcium and oxalic acid together increases the chance that crystals will form in the gut, preventing the oxalic acid from reaching the blood and then the kidneys. One small study found that in those people consuming the recommended daily calcium intake, high oxalic acid intake did not increase the risk of kidney stones at all.
• Avoid consuming too much protein or vitamin C: Oxalic acid is produced within the body as a byproduct of amino acid and vitamin C metabolism, so avoid consuming more than required in order to reduce oxalic acid levels.
• Consume less sodium: High sodium intake leads to more calcium in the urine, which could increase the risk of calcium oxalate crystals forming.
• Avoid consuming fibre and oxalic acid at the same time: Fibre is very important, but there’s some evidence that it enhances the antinutrient properties of oxalic acid.
• Look after your gut: Some gut bacteria are able to metabolise oxalic acid, so maintaining a healthy gut microbiota may reduce the amount of oxalic acid that reaches the blood.

Other Conditions And Reasons To Avoid Oxalic Acid

What about the claim that oxalic acid can cause other problems like arthritis? There are some situations in which oxalate crystals might form outside of the kidneys, such as in the joints or skin. This rare condition is called oxalosis and can only happen in people with other chronic conditions. There are also a few specific cases in which you might want to pay more attention to oxalic acid intake. Below are some examples. If you have a reason to think you would benefit from avoiding oxalic acid-containing foods, ask your doctor about it.

• Genetic conditions: Some people have a genetic condition that causes them to produce too much oxalic acid.
• Kidney failure: Since the urine is the only route by which oxalic acid can be removed from the body, kidney failure will result in oxalate crystals forming elsewhere.
• Kidney stones: If you have kidney stones and oxaluria (high oxalate in the urine), you may be advised to reduce oxalic acid intake.
• Gastrointestinal conditions: Conditions that affect the absorption of fat in the gut, such as inflammatory bowel diseases, may increase the amount of oxalic acid that reaches the blood.
• Vulvodynia: Some women experience persistent vulval pain in a condition called vulvodynia. The cause is not known, and studies so far have found no relationship between oxalate and vulvodynia. However, there is a small amount of evidence that reducing oxalic acid consumption might reduce symptoms.

The Take-Home Message

Unless you are consuming a lot of them or have certain medical conditions, there’s no reason to avoid healthy foods containing oxalic acid. The downsides of oxalic acid can be counteracted, mainly by consuming more water and calcium.