Is oxalic acid in spinach bad for you?

Spinach is well known as a super healthy vegetable that is high in vitamins, minerals, and antioxidants. However, spinach also contains significant amounts of oxalic acid, which has caused some controversy regarding the health effects of eating spinach.

What is Oxalic Acid?

Oxalic acid is an organic compound found in many plant foods like leafy greens, nuts, grains, fruits and vegetables. It plays a role in the metabolism processes of plants and animals.

In plants, oxalic acid helps to get rid of excess calcium by binding with it. It also provides protection against insects and fungal infections. In the human body, oxalic acid binds with minerals like calcium and iron to form crystals that can contribute to kidney stones.

Oxalic Acid Content in Spinach

Spinach contains higher levels of oxalic acid compared to most other vegetables. In 100 grams of raw spinach, there is approximately 0.97g of oxalic acid.

Cooking spinach significantly reduces its oxalate content. Boiling spinach can reduce oxalates by 30-87%, while steaming reduces oxalates by 8-53%.

Frozen spinach generally has lower oxalate levels than fresh spinach. However, canned spinach typically has higher oxalate levels because the leaves are cooked directly in the can, which helps to better extract oxalates.

Benefits of Oxalic Acid

Although it can promote kidney stones in excess, oxalic acid is not entirely bad and actually has some benefits when consumed in moderation from whole foods like spinach.

Potential benefits of oxalic acid include:

• Antioxidant activity – Oxalic acid acts as an antioxidant, helping to protect cells from damage
• Chelation of heavy metals – Binds to heavy metals like lead and mercury to make them easier to eliminate from the body
• Antimicrobial effects – Oxalic acid may have antimicrobial actions against some bacteria, fungi and enveloped viruses

Negative Effects of Oxalic Acid

There are also some potential negative effects of oxalic acid to be aware of:

• Kidney stones – Oxalate can bind with calcium to form calcium oxalate kidney stones. Those with a history of kidney stones may need to limit high-oxalate foods.
• Mineral absorption – The oxalic acid in spinach can inhibit absorption of some minerals like calcium, magnesium and iron.
• Vulvodynia – Some women are sensitive to oxalates and get vulvar pain after eating high-oxalate foods.
• Oral absorption – Oxalic acid can cause burning and irritation when raw spinach is eaten in large amounts.

Oxalates and Kidney Stones

One of the biggest concerns with oxalic acid is its ability to promote kidney stones in susceptible individuals. Kidney stones develop when urine becomes too concentrated, allowing minerals like calcium and oxalates to crystalize and form stones.

About 75% of kidney stones are primarily composed of calcium oxalate. Even small amounts of oxalates in the diet can contribute to kidney stone development in those prone to them.

Research shows that consuming foods high in oxalates like spinach does appear to increase the risk of calcium oxalate kidney stones. One study found that consuming the highest amount of dietary oxalate increased kidney stone risk by 20% compared to the lowest intake.

However, other nutrients in spinach like magnesium and potassium may help offset this risk. One study found that while higher oxalate intake was linked to more kidney stones, eating more spinach was associated with a lower risk.

Who May Need to Limit Oxalates?

For most healthy adults, moderate amounts of oxalates from spinach and other healthy plant foods are not a major concern. However, some individuals may benefit from restricting dietary oxalates.

Those who may want to limit oxalates include:

• People with a history of calcium oxalate kidney stones
• Individuals with malabsorption issues like Crohn’s disease or gastric bypass
• People with vulvodynia or oxalate sensitivity
• Anyone with impaired kidney function

For people prone to kidney stones, the recommendation is generally to keep total oxalate intake under 40-50 mg per day. Consuming vitamin C supplements along with foods rich in oxalates can increase kidney stone risk as well.

Tips to Reduce Oxalates in Spinach

Here are some effective ways to reduce oxalates while still enjoying spinach:

• Boil, steam or sauté spinach instead of eating it raw
• Pour out the boiling water after cooking spinach
• Use frozen spinach where the oxalates have been leached out into the water
• Limit portion sizes of spinach to 1-2 cups per day
• Drink plenty of fluids to dilute urine
• Increase intake of calcium, magnesium and potassium

Healthy Ways to Eat Spinach

Here are some healthy, low-oxalate ways to incorporate spinach into your diet:

• Add handfuls of spinach to omelets, frittatas and egg scrambles
• Stir chopped spinach into soups, stews and chili
• Mix spinach with lentils, beans or chickpeas for extra protein
• Blend cooked spinach into hummus, dips and sauces
• Add a cup of cooked spinach to smoothies
• Make a spinach salad with baby spinach, strawberries, avocado and nuts

The Oxalic Acid in Spinach: Final Thoughts

Here is a summary of the key points regarding oxalic acid in spinach:

• Spinach contains higher amounts of oxalic acid than many other vegetables
• Oxalic acid may interfere with mineral absorption and promote kidney stones when consumed in excess
• Cooking spinach significantly reduces its oxalate content
• People prone to kidney stones may need to limit dietary oxalate sources like spinach
• For most people eating a healthy diet, oxalates in moderation are not a major concern
• Enjoy spinach as part of an overall healthy and balanced diet, focusing on variety and proper cooking techniques

In general, spinach is a very healthy food that provides protein, vitamins, minerals, and antioxidants. Despite containing oxalic acid, spinach can be part of a healthy diet when portion sizes are controlled and preparation methods are used to reduce oxalate levels.

Oxalic Acid Levels in Spinach

Food	Serving Size	Oxalic Acid (mg)
Raw spinach	1 cup	656
Boiled spinach	1 cup	102
Canned spinach	1 cup	843
Frozen spinach	1 cup	459

As shown in the table, cooking spinach significantly reduces the oxalic acid content. Boiling spinach can lower oxalates by 70-90% compared to raw leaves. Canned spinach retains more oxalates due to the cooking method.

Conclusion

Overall, while spinach does contain oxalic acid, it is still considered one of the healthiest vegetables you can eat. The nutrients, vitamins and health benefits of spinach far outweigh concerns about its oxalate content.

Using proper cooking techniques and not over-consuming spinach should keep oxalates at a safe level for most healthy people. For those prone to kidney stones, limiting dietary oxalate sources like spinach may be wise.