Know Your Stones...Protect Your Kidneys

Author: Betty Kovacs, MS, RD
Medical Editor: William C. Shiel Jr., MD, FACP, FACR

Do you know your kidney stone?

The unfortunate thing about kidney stones is that once you have had one there is a significant chance that you will have another one. Fortunately, there are things that you can do that may help prevent future occurrences.

One of the keys to prevention is to learn about your previous kidney stones. If you pass a stone and can save it, your doctor can have it analyzed to determine precisely what kind of stone it was. Your doctor may order blood and urine tests as well. The tests will be checking your urine volume and levels of acidity, calcium, oxalate, sodium, citrate, creatinine, and uric acid. Knowing what caused your stone will make preventing future stones more likely.

How can your diet increase the risk for calcium stones?

Approximately four out of five kidney stones are calcium stones. These stones are often a combination of calcium and oxalate, but can also be a combination of calcium and phosphate or a combination of all three. A great deal of research has uncovered dietary factors that can lead to the development of these stones.

The beef about animal protein: Protein is an essential nutrient needed for numerous functions in our body. The average American consumes about twice the RDA for protein each day with the majority of it coming from animal sources. Some research has shown a link between kidney stones and diets high in animal protein, while others have found no difference in stone formation in animal versus plant protein consumption. If the majority of your meals contain a source of meat (for example, chicken, turkey, eggs, beef, seafood, pork, or dairy foods), then the recommendation would be to cut back on the quantity and/or frequency that these are consumed. Here are some ways to get protein from plant sources:

  • Soy cheese
  • Tofu
  • Beans
  • Chic peas
  • Lentils
  • Soy milk
  • Whole grains
  • Vegetables
  • Nuts (if oxalates are not a problem)

Shake off the salt. Research is clear on the fact that the sodium found in salt can cause problems by increasing the amount of calcium that you excrete in your urine, which in turn increases your risk of another kidney stone developing. The recommendation is to consume a maximum of 2,000 to 3,000 milligrams (mg) of sodium a day. The main source of sodium in our diets comes from processed and prepared foods. The sodium is used as a preservative and taste enhancer in foods such as canned foods, frozen foods, and cold cuts. Many of these products are now available in low-sodium versions, so be sure to read the label. The food label guidelines for sodium are as follows:

  • Sodium-free: less than 5 mg per serving


  • Very low sodium: 35 mg or less per serving or, if the serving is 30 grams (g) or less or 2 tablespoons or less, 35 mg or less per 50 g of the food


  • Low-sodium: 140 mg or less per serving or, if the serving is 30 g or less or 2 tablespoons or less, 140 mg or less per 50 g of the food


  • Light in sodium: at least 50% less sodium per serving than average reference amount for same food with no sodium reduction


  • Lightly salted: at least 50% less sodium per serving than reference amount


  • Reduced or less sodium: at least 25% less per serving than reference food

The salt that you add while cooking or eating can easily put you over your limit for the day. Each teaspoon of salt contains about 2,300 mg of sodium. Some techniques for keeping your sodium intake down are:

  • Prepare food yourself when possible


  • Choose fresh or frozen vegetables


  • Limit or avoid processed, cured or pickled foods


  • Try sodium free seasonings for flavor. Some great options are pepper, fresh garlic, garlic power, fresh onion, onion powder, lemon juice and vinegar


  • Replace high sodium sauces with dry mustard, vinegar, or homemade low sodium sauces


  • When eating out, ask for the sauce on the side and add it sparingly

Too much of a good thing: When it comes to vitamins, more is not always better. For this reason, tolerable upper limits (UL) have been set to let people know what level they need to stay below to avoid any harmful health consequences. There is some evidence to suggest that ascorbic acid (vitamin C) taken in high doses can increase stone formation in people who are at risk. In order to avoid this increased risk, you will need to stay below the UL of 2,000 mg/day that has been set for ascorbic acid. An 8-ounce cup of orange juice contains only about 130 mg of vitamin C, so the most likely way to exceed the safety limit would be through supplements. If you do take a vitamin supplement, be sure to read the labels carefully and speak with your physician if you have any questions.