About 80 percent of kidney stones are made up of crystals of calcium oxalate or calcium phosphate. Animal protein also reduces the production of urinary citrate, which is a natural inhibitor of calcium stones. Current recommendations are to eat less than six ounces of meat or fish a day and include plenty of vegetables and fruits in the diet. However, people who have a history of calcium oxalate stones may need to be a bit careful about the type of fruits and vegetables they choose. Certain fruits and vegetables and other foods such as chocolate contain large amounts of the compound oxalate, which can aggravate the tendency to form calcium oxalate stones.
Oxalates are particularly high in spinach, rhubarb, beets, strawberries, nuts and nut butters.
Oxalates are also a by-product of vitamin C metabolism, and people who tend to form calcium oxalate stones are advised to limit vitamin C supplement to 500 mg a day. People who get calcium stones often ask if they need to limit calcium in their diets. In many instances, increasing dietary calcium may actually help to forestall stone formation. Too low a level of calcium in the blood can cause calcium to be pulled from the bones, which leads to more calcium in the urine and an increased risk of stone formation. In addition, this can increase the likelihood of bone disease in women.