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What Is Calcium Oxalate?

By Shelley Moore ; Updated April 18, 2017

Calcium is an essential mineral, while oxalate is a bitter component of certain plants. The two bind together in the digestive system. The combination can cause calcium oxalate kidney stones when an individual susceptible to this problem consumes too much of these substances, and does not drink enough fluids to flush calcium oxalate crystals from the kidneys.


Approximately 80 percent of all kidney stones are made of calcium oxalate, according to Brigham and Women's Hospital. Kidney stones consist of minerals that normally leave the kidney through urine, but these crystals can lodge in the kidney and grow larger. Five percent of Americans develop kidney stones, as noted by Brigham and Women's Hospital. Men and individuals with a family history of kidney stones are more prone to the disorder. The risk continually increases after age 40.


Oxalate is a much bigger factor in kidney stone formation than calcium is, according to Brigham and Women's Hospital. Consuming 1,000 to 1,200 mg of calcium per day can help prevent kidney stones, because calcium binds with oxalate in the digestive tract and prevents the oxalate from being excreted in urine. Free oxalate in the urine increases the tendency to form kidney stones.

Foods to Eat

Because too much calcium also can increase the chances of forming calcium oxalate stones, it's best to obtain your calcium through diet rather than supplements. Good sources of calcium, as noted by Brigham and Women's Hospital, include low-fat or fat-free dairy products, including milk, cheese and yogurt. You can also obtain calcium by eating broccoli, collard greens, sardines, almonds, black beans, tofu, and calcium-fortified orange juice and soy milk.

Foods to Avoid

Limiting foods and spices high in oxalate content also can help prevent calcium oxalate stones. A list of oxalate-containing substances compiled at Dr. Duke's Phytochemical and Ethnobotanical Databases includes leafy green vegetables and many other vegetables, soybeans, lentils, pumpkin, star fruit, bananas, buckwheat, almonds, oats, wheat, black and white pepper, poppy seeds and ginger.


Drink 8 to 12 cups of fluid per day to prevent calcium oxalate and other types of kidney stones, as advised by Brigham and Women's Hospital. This can include coffee. Drinking sufficient fluid also can flush out an existing stone if it is not too large. Larger stones may require lithotripsy, which is a procedure that breaks up the stone with shock waves, or a minor surgical procedure to remove them.

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