Practical Practitioner
By: Pamela Egan, FNP-C CDE
Kidney Stone Prevention
Dear Pam,
Is it true that one shouldn’t eat calcium products once they’ve had a kidney stone?
Experts now think that limiting calcium in your diet is not necessary to prevent kidney stones. This is important because the risk of developing osteoporosis as you get older is much greater if you don’t get enough calcium.
Oxalate is another substance that is excreted in the urine. Experts now think that too much oxalate in the urine is very important in kidney stone formation. Oxalate is formed by the body, but it is also found in food.
When eating foods that contain oxalate, the oxalate is absorbed and then excreted in the urine. Dietary calcium can help because calcium binds up the oxalate in the gut. When this happens, the bound oxalate is not absorbed.
There are several dietary changes that can help prevent kidney stones, depending on what type of stones you have.
Don’t change your diet without talking with your healthcare provider first. Together, you can decide which diet changes are best for you. There is also medication to help prevent kidney stones.
Getting plenty of fluids is extremely important, and water is best. Fluids help to dilute the urine and flush away substances that form kidney stones.
Crystals are much less likely to form when the urine is dilute. You should try to drink 2 to 3 liters per day.
If you have calcium oxalate kidney stones, you may want to limit how much animal protein and sodium you eat. Eating too much animal protein and salt increases you chance of forming kidney stones. Limit your intake of foods high in oxalate.
Decreasing the amount of oxalate you get from the foods you eat will decrease the amount of oxalate that is absorbed.
Examples of these types of foods are nuts (walnuts, peanuts, almonds, hazelnuts, etc.), spinach, okra, beets, rhubarb, strawberries, cranberries, soy, wheat bran, brown rice, chocolate, coffee, tea and cocoa.
A good calcium supplement is calcium citrate (Citracal, etc.). Citrate is one of the substances in the urine that can help prevent kidney stones from forming. You’ll need to take calcium supplements with meals, so that the calcium is available to bind the oxalates in the intestines.
Hypercalciuria is an important and common risk factor for the formation of kidney stones.
In fact, about 80 percent of kidney stones contain calcium and most of these are made up of calcium oxalate. Some calcium stones contain calcium phosphate.
A smaller proportion of stones contain uric acid, are struvite stones (caused by urinary tract infections), or are cystine stones. Once a kidney stone forms, there is a 50 percent probability that another stone will form within five to seven years without treatment. Initial treatment of recurrent kidney stones generally involves changes in dietary habits.
The most current studies provide good evidence that a normal-calcium, low protein, low-salt diet more effectively reduces the risk of recurrent kidney stones than a diet low in calcium.
This article was originally published August 26, 2002 in The St. Tammany News.
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