Oxalic Acid (oxalate): What It Is, Risks, How To Avoid It, And More

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Medical News TodaySubscribeWhat is oxalic acid (oxalate), and is it dangerous?

Medically reviewed by Alana Biggers, M.D., MPH — Written by Zia Sherrell, MPH — Updated on October 1, 2025

What is it?
Uses
Health risks
Absorption
Consumption
How to avoid it
Summary

Oxalic acid is a naturally occurring compound in many fruits, vegetables, nuts, and whole grains. While small amounts of oxalic acid are not harmful, this compound can inhibit the absorption of other important nutrients.

Due to its ability to reduce nutrient absorption, some people refer to oxalic acid, or oxalate, as an anti-nutrient. In some people, it can also increase the risk of kidney stones.

Certain gut bacteria can metabolize, or break down, oxalic acid. This prevents it from binding to minerals and affecting nutrient absorption.

This article looks at oxalic acid and its associated risks in more detail. It also lists dietary sources of the compound and explains how people can decrease their intake.

What is it?

An image of a piece of spinach. — Flavia Morlachetti/Getty Images

Oxalic acid is a common organic compound. A range of living organisms — including fungi, bacteria, plants, animals, and humans — produce it.

Technically, oxalate occurs when the oxalic acid in plants binds to minerals. However, many people use the terms interchangeably.

The body can either produce oxalate as a waste product or obtain it from the diet.

Oxalate can combine with other minerals in the body to form compounds such as calcium oxalate and iron oxalate. People can then eliminate these oxalate compounds in the urine or stool.

However, some individuals with high oxalate levels may develop kidney stones.

What is it used for?

Laboratories may use oxalic acid and oxalate salts as anticoagulants in blood specimens.

Although oxalic acid naturally occurs in plants and humans, it also has a variety of uses in industry. These uses include:

removing rust
removing stains
stripping and cleaning
removing wax
cleaning wood
dyeing textiles

Health risks

Oxalate is harmless in small amounts. However, higher levels may reduce the body’s mineral absorption and contribute to kidney stone formation.

Nutrient absorption

People refer to oxalates as anti-nutrients. This is because they bind to certain minerals and prevent the body from absorbing and utilizing them.

One good example is spinach. Although it is rich in the important nutrients calcium and magnesium, it is also high in oxalate. The oxalate forms a complex with these minerals and can inhibit absorption.

Kidney stones

The other concern with oxalate is that it can contribute to kidney stones.

Most people have a small amount of oxalate and calcium in the urinary tract at some point. Usually, they remain dissolved, and there are no associated problems.

However, in some people, the compounds form crystals and then kidney stones. Research has shown that this is a particular problem if oxalate levels are high and urinary volume is low.

There are several types of kidney stones, which comprise different minerals, but calcium oxalate is the most common. Therefore, if a person is prone to developing kidney stones, their doctor may advise them to reduce their intake of oxalate-rich foods. They should also consume enough calcium and avoid vitamin C supplements.

»FIND CARE:Find a kidney health specialist near you today

The gut and oxalate absorption

Certain bacteria in the digestive system can metabolize some dietary oxalate before it binds to minerals, preventing its potentially harmful effects.

A type of gut bacteria called Oxalobacter formigenes breaks down oxalate and uses it as energy. Having this bacteria in the gut microbiome significantly reduces the amount of oxalate in a person’s body.

Many people have O. formigenes in their gut. According to research, it is present in the feces of about 60 to 80% of adults.

Some people who experience recurrent calcium oxalate kidney stones have less of this bacteria.

Certain factors, such as taking antibiotics, can reduce the number of good bacteria in the gut. Additionally, people with altered gut function, such as those with inflammatory bowel disease (IBD), have an increased risk of developing kidney stones.

How people consume it

People typically consume oxalate through dietary sources. Almost all plants, including fruits and vegetables, contain oxalates, having the highest concentration in the leaves and seeds. However, the amount they contain varies considerably.

Vegetables that are particularly high in oxalate include:

spinach
kale
swiss chard
sweet potatoes
rhubarb
beets
potato skins

Other dietary sources rich in oxalate include:

black tea
soy
cocoa
nuts, such as almonds, Brazil nuts, and pine nuts

The amount the body can absorb from foods depends on the quantity of soluble oxalates the foods contain and the bioavailability of these oxalates. For example, tea has a significantly higher rate of oxalate absorption than spinach or rhubarb.

The method of food preparation and cooking can also affect the oxalate content. Soaking certain vegetables and legumes can reduce the amount of oxalate they contain.

How to avoid it

The best way to avoid oxalate is to reduce the intake of oxalate-rich foods.

It is important to eat a variety of fruits and vegetables. However, if a person is concerned about the number of oxalates in certain foods, they can replace them with low oxalate alternatives. Some examples include:

High oxalate food	Low oxalate alternative
kale	broccoli
spinach	asparagus
potatoes	cauliflower
rhubarb	apples
beets	cherries
black tea	fruit tea
dark chocolate	white chocolate

Boiling vegetables also reduces their oxalate content. Research shows that boiling could remove up to 76% of oxalates, depending on the vegetable.

It is also important to eat enough dietary calcium. This mineral can bind to oxalate in the digestive system and reduce how much the body absorbs. Therefore, eating milk, yogurt, or cheese alongside foods containing oxalates can reduce the likelihood of developing issues such as kidney stones.

Summary

Oxalate is a compound present in many plant-based foods, including spinach, chard, and kale.

In the digestive system, oxalate can form complexes with minerals such as calcium and interfere with their absorption. Additionally, a high oxalate diet may lead to some people developing kidney stones.

Doctors may advise some individuals to consume a low-oxalate diet. They can do this by replacing high-oxalate foods with low-oxalate alternatives, boiling vegetables, and eating foods rich in calcium alongside high-oxalate foods.

Biology / Biochemistry
Nutrition / Diet

How we reviewed this article:

SourcesMedical News Today has strict sourcing guidelines and relies on peer-reviewed studies, academic research institutions, and medical journals and associations. We only use quality, credible sources to ensure content accuracy and integrity. You can learn more about how we ensure our content is accurate and current by reading our editorial policy.

Akter S, et al. (2020). Interactions between phytochemicals and minerals in Terminalia ferdinandiana and implications for mineral bioavailability.https://www.frontiersin.org/articles/10.3389/fnut.2020.598219/full
Arias-Rico J, et al. (2020). Study of edible plants: Effects of boiling on nutritional, antioxidant, and physicochemical properties.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7278626/
Calcium oxalate stones. (n.d.).https://www.kidney.org/atoz/content/calcium-oxalate-stone
D'Alessandro C, et al. (2019). Which diet for calcium stone patients: A real-world approach to preventive care.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6566930/
Joshi V, et al. (2021). Regulation of oxalate metabolism in spinach revealed by RNA-seq-based transcriptomic analysis.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8157348/
Kidney stone diet plan and prevention. (n.d.).https://www.kidney.org/atoz/content/diet
Mitchell T, et al. (2018). Dietary oxalate and kidney stone formation.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6459305/
Oxalobacter formigenes. (n.d.).https://www.sciencedirect.com/topics/immunology-and-microbiology/oxalobacter-formigenes
Palmieri F, et al. (2019). Chapter two — oxalic acid, a molecule at the crossroads of bacterial-fungal interactions.https://www.sciencedirect.com/science/article/abs/pii/S0065216418300510
Shi L, et al. (2018). Changes in levels of phytic acid, lectins and oxalates during soaking and cooking of Canadian pulses.https://pubmed.ncbi.nlm.nih.gov/29580532/

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Medically reviewed by Alana Biggers, M.D., MPH — Written by Zia Sherrell, MPH — Updated on October 1, 2025

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Tag » What Is Oxalic Acid Used For

Oxalic Acid (oxalate): What It Is, Risks, How To Avoid It, And More

What is it?

What is it used for?

Health risks

Nutrient absorption

Kidney stones

The gut and oxalate absorption

How people consume it

How to avoid it

Summary

How we reviewed this article:

Latest news

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