Oxalates are okay for most people, but people with altered bowel function may want to limit their intake. Research does not show that oxalates cause autism or chronic vaginal pain, but they may increase the risk of kidney stones in some people.
Oxalic acid is an organic compound found in many plants, including leafy greens, vegetables, fruits, cocoa, nuts, and seeds (1).
In plants, it often combines with minerals to form oxalates. The terms “oxalic acid” and “oxalate” are used interchangeably in nutritional science.
Your body can produce oxalates on its own or get it from food. Vitamin C can also be converted to oxalate through metabolism (2).
When ingested, oxalates can combine with minerals to form compounds including calcium oxalate and iron oxalate. It mainly occurs in the colon, but can also occur in the kidneys and other parts of the urinary tract.
However, for sensitive people, a diet high in oxalates may increase the risk of kidney stones and other health problems.
Oxalate is an organic acid found in plants, but it can also be synthesized by the body. It binds to minerals and is linked to the formation of kidney stones and other health problems.
One of the main health concerns associated with oxalates is that they can bind to minerals in the intestines and prevent them from being absorbed by the body.
For example, spinach is rich in calcium and oxalates, which prevent the body from absorbing large amounts of calcium (4).
However, it is important to remember that only some minerals in foods bind to oxalates.
Although calcium absorption from spinach is reduced, consuming milk and spinach together does not affect the absorption of calcium from milk (4).
Oxalates can bind to minerals in the intestines and interfere with the absorption of some of them, especially when combined with fiber.
Normally, calcium and small amounts of oxalate are present together in the urinary tract, but they remain dissolved and do not cause any problems.
However, sometimes they combine to form crystals. In some people, these crystals can lead to stone formation, especially if oxalate levels are high and urine output is low (1).
Small stones usually do not cause any problems, but large stones can cause severe pain, nausea, and blood in the urine as they pass through the urethra.
Therefore, people with a history of kidney stones may be advised to minimize their intake of foods high in oxalates (7, 8).
However, complete oxalate restriction is no longer recommended for all patients with kidney stones. This is because half of the oxalate found in urine is produced by the body rather than absorbed from food (8, 9).
Most urologists now prescribe a strict low-oxalate diet (less than 100 mg per day) only to patients with elevated urinary oxalate levels (10, 11).
Therefore, it is important to test from time to time to determine how much restriction is necessary.
Foods high in oxalates may increase the risk of kidney stones in susceptible people. Recommendations for limiting oxalate intake are based on oxalate levels in urine.
Others suggest that oxalates may be associated with vulvodynia, which is characterized by chronic, unexplained vaginal pain.
Based on the study results, researchers believe that both conditions are unlikely to be caused by dietary oxalates (12, 13, 14).
However, in a 1997 study where 59 women with vulvodynia were treated with a low-oxalate diet and calcium supplements, nearly a quarter experienced improvement in symptoms (14).
The study authors concluded that dietary oxalates may aggravate rather than cause the disease.
Some online anecdotes do link oxalates to autism or vulvodynia, but few studies have examined the possible connection. Further research is needed.
Some people believe that eating foods high in oxalates can cause autism or vulvodynia, but current research does not support these claims.
Some proponents of the low-oxalate diet say it’s best for people to avoid foods rich in oxalates because they can have negative health effects.
However, everything is not so simple. Many of these foods are healthy and contain important antioxidants, fiber, and other nutrients.
Many foods containing oxalates are tasty and healthy. For most people, avoiding them is unnecessary and may even be harmful.
Some of the oxalates you eat are broken down by bacteria in your gut before being combined with minerals.
One of these bacteria, Oxalobacterium oxytogenes, actually uses oxalate as an energy source. This significantly reduces the amount of oxalate absorbed by the body (15).
However, some people don’t have as many of these bacteria in their gut because antibiotics reduce the number of O. formigenes colonies (16).
Additionally, studies have shown that people with inflammatory bowel disease have an increased risk of developing kidney stones (17, 18).
Likewise, elevated levels of oxalate have been found in the urine of people who have had gastric bypass surgery or other procedures that alter bowel function (19).
This suggests that people taking antibiotics or experiencing gut dysfunction may benefit more from a low-oxalate diet.
Most healthy people can eat foods rich in oxalates without problems, but people with altered bowel function may need to limit their intake.
Oxalates are found in almost all plants, but some contain very large amounts and others contain very small amounts (20).
Serving sizes may vary, meaning that some “high oxalate” foods, such as chicory, may be considered low oxalate if the serving size is small enough. Here’s a list of foods that are high in oxalates (more than 50 mg per 100-gram serving) (21, 22, 23, 24, 25):
The amount of oxalate in plants ranges from very high to very low. Foods containing more than 50 milligrams of oxalates per serving are classified as “high oxalate.”
People on a low-oxalate diet because of kidney stones are usually asked to consume less than 50 milligrams of oxalate per day.
A balanced and nutritious diet can be achieved with a daily oxalate content of less than 50 mg. Calcium also helps reduce the absorption of oxalates.
However, healthy people who want to stay healthy don’t need to avoid nutrient-dense foods just because they’re high in oxalates.
Our experts continually monitor health and wellness and update our articles as new information becomes available.
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