Eating Right to Prevent Pain:
How Diet can Prevent Kidney Stones
Thomas J. Stormont, MD
It is often said that a kidney stone attack is the most painful event a human can experience. Unfortunately for us, stones are common, unpredictable and tend to recur (50% reform within 5 yrs if untreated with diet or medication). So if you have ever had a stone, have a family history of stones, or just want to know how to prevent them, this article is for you. The following will be a brief discussion of general dietary recommendations for the most common stones - calcium oxalate and uric acid.
What makes kidney stones?
Stone formation is complicated and does involve a genetic component (some people unfortunately make stones even when they do everything right). Generally however, their production can partly be understood by basic chemistry. Low volume, highly concentrated urine results in the precipitation of crystals, which can aggregate and lead to stone formation. Consider an attempt to dissolve salt (a solute) in a glass of water (the solvent) - a few grains of salt - will easily dissolve in a glass of water, but a tablespoon will have more trouble. This is because the water gets saturated with the salt, and at a certain concentration, the water can dissolve no more. Simply put, dietary prevention is thus focused mainly upon increasing the solvent (water) and decreasing the salt (calcium, oxalate) in the urine.
The most important factor - Fluids!
Generally it is recommended increasing urine volume to at least 2 liters/daily, although some recommend trying to achieve 3 liters. Keep in mind that it is not the amount of fluid consumed, but rather the amount of fluid voided that is important. This is because people who live in hot environments or exercise more will require more fluid intake to achieve the 2 liter/day minimum. Since it isn't often practical to measure the daily volume of urine, keeping it clear and "pale" yellow is a good indicator that you are well hydrated. Also, it is important to remember that this dilution of urine should be all day long, which may require more trips to the bathroom at night.
The simple answer to what fluid is best is water. There is no good data on how the mineral content of water affects stone formation, so while the type of water is not critical, the amount ingested clearly is.
Although there is some controversy, in general, stone formers should avoid excess caffeine, black tea, grapefruit and apple juices. Alcohol and milk in general have not been shown to cause stones. Lemonade clearly is the best fluid besides water, because it is rich in citrate, a stone inhibitor.
Calcium Intake
Sufficient calcium is required to prevent osteoporosis, so while reducing urine calcium should be a goal for stone formers, it should NOT be done by reducing dietary calcium. In fact, recent studies have shown that adequate calcium intake, especially when combined wth other dietary measures mentioned in this article, actually is associated with decreased stone formation. The U.S. Recommended Daily Allowance of calcium is generally 1000 mg/day for men and women - ideally by ingesting calcium rich foods rather than with supplements.
Dietary Oxalate
It is clear that urinary oxalate levels are more important than urinary calcium levels, in the formation of the most common type of stone, calcium oxalate. Patients with these stones should avoid foods high in oxalate. The highest levels are found in chocolate, nuts, black tea, beans, beets and spinach. Also, megadoses of Vitamin C should be avoided.
Sodium
High sodium intake is associated with greater calcium levels in the urine. Sodium is a common preservative in many foods, so even if you don’t salt your foods it is easy to exceed the 2,000 mg/day that is recommended for stone formers.
Animal Protein
Like sodium, high dietary protein leads to increased calcium excretion in the urine, along with uric acid. As expected, vegetarians form stones at less than 1/2 the rate of those eating a mixed diet. Thus reduction of animal protein to 12 ounces/day is recommended, and protein from plants can be substituted without problem, keeping an eye on the oxalate content (nuts, beans).
Weight Loss
There is gathering evidence that increased body weight is a risk factor for stone formation.
Conclusions
While talking about dietary changes is easier than actually doing them, clearly the most important thing to do is to keep the urine dilute. Diet alone can reduce the chance of making new stones, but for some there may be more testing with special blood and urine chemistry studies to help direct more specific dietary changes or medications.
