What Are Oxalates?

A 2021 case report in the Journal of Medical Case Reports describes oxalate as a simple dicarboxylic acid often found in a variety of plants and leafy vegetables. The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) says calcium stones, including calcium oxalate and calcium phosphate stones, are the most common types of kidney stones, and that calcium oxalate stones are more common than calcium phosphate stones.

NIDDK says people who have had calcium oxalate stones may want to avoid nuts and nut products, peanuts, rhubarb, spinach and wheat bran to help reduce the amount of oxalate in their urine. It says that even though calcium sounds like it would be the cause of calcium stones, it is not, because in the right amounts calcium can block other substances in the digestive tract that may cause stones, and it advises talking with a health care professional about how much calcium to eat to help prevent more calcium oxalate stones and support strong bones.

Very high intake has been linked to kidney injury in case reports. The 2021 report describes acute oxalate nephropathy associated with eating large quantities of green vegetables in a patient with chronic kidney disease, in whom imaging showed no kidney stone but a kidney biopsy found tubular injury, atrophy and scarring with dense calcium oxalate crystal deposits. A 2024 case report in Cureus describes a patient with oxalate nephropathy who drank a daily blend of green leafy vegetables including spinach and kale with an orange and a lemon, foods the authors say are high in oxalate and contribute significantly to dietary oxalate intake.