Kidney Stones - Prevention

Calcium Supplements. Evidence on calcium supplements is mixed, although in general many studies suggest that they reduce oxalate levels and so help prevent calcium oxalate stones. One study suggested that taking 500 mg of calcium supplements a day regularly may "reprogram" the intestines to absorb less calcium and so be protective. Experts generally advise that calcium supplementation within dosage recommendations, approximately 1,200 mg per day, remains safe. In one study, however, women who took calcium supplements had a 20% higher risk for stones. Research indicates that dosages of calcium above 2,000 mg per day are clearly associated with the formation of stones. Some experts speculate that this higher risk may occur because supplements are often taken in the morning, either without food or with breakfast, which is typically low in oxalates. Taking supplements with later meals may not incur the same risk.

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Calcium Restriction in Certain Cases. Some calcium stone patients may need to restrict calcium, such as those whose stones are caused by genetic defects in which the intestine over-absorbs calcium. More studies are needed to define this group precisely.

Fiber-Rich Foods and Their Compounds

Fiber may be beneficial for people with kidney stones. In addition, some fiber-rich foods may contain compounds that help protect against kidney stones. A wide variety of high-fiber plant foods contain a compound called phytate (also called inositol hexaphosphate, InsP6, or IP6), which appears to help prevent crystallization of calcium salts, both oxalate and phosphate. Phytate is found in legumes and wheat and rice bran. (Soybeans are also rich in phytate but they are also very high in oxalates, so the overall effects of soy on kidney stones are not clear.)

Purine Restriction in People at Risk for Uric Acid Stones

A high intake of purines can increase the amount of uric acid in the urine, so those at risk for uric acid stones should reduce their intake of foods that contain purines. They include beer and other alcoholic beverages, anchovies, sardines, yeast, organ meats (e.g., liver, kidneys), legumes (e.g., dried beans, peas, and soybeans), mushrooms, spinach, asparagus, cauliflower, and poultry.

Oxalate Restriction in Hyperoxaluria

Most people with calcium oxalate stones should not avoid oxalate-rich foods unless the doctor specifically recommends a restrictive diet. Oxalate binds with calcium in the intestine, which may actually reduce calcium absorption. Some studies, in fact, indicate that eating foods containing oxalates and calcium together may reduce the risk of stones. Most of the foods that contain oxalates are very important for good health. Restricting oxalates may be particularly harmful in people with bowel disorders marked by malabsorption.

Foods high in oxalic acid include beets, soy, beet tops, black tea, chenopodium, chocolate, cocoa, dried figs, ground pepper, lamb, lime peel, nuts, parsley, poppy seeds, purslane, rhubarb, sorrel, spinach, and Swiss chard.
Foods containing moderate amounts of oxalates include beans (green and wax), blackberries, blueberries, carrots, celery, coffee (roasted), concord grapes, currants, dandelion greens, endive, gooseberries, lemon peel, okra, green onions, oranges, green peppers, black raspberries, strawberries, and sweet potatoes.