Kidney Stones Update
Chester J. Zelasko, Ph.D. | May 26, 2006

Kidney stones are painful--just ask anyone who’s had one. Treatment for kidney stones has relied on lifestyle changes that include avoiding calcium. However, that recommendation may be changing when it comes to calcium oxalate stones--a type of kidney stone that afflicts most people who get kidney stones. This Newsletter will review the latest dietary recommendations on preventing calcium oxalate kidney stones published in the Canadian Medical Association Journal (1). It is critical that you talk with your doctors before making any lifestyle changes--they know your specific condition.

Causes of Kidney Stones
The specific cause of kidney stones remains elusive. The risk of developing kidney stones is thought to be a combination of genetic and environmental factors. While the gene or genes have not been discovered, the environmental causes--read that as lifestyle--have been identified for the most part. Here are some things you can do to reduce kidney stones.

Increase Fluid Intake
The key to reducing kidney stones is to increase urine output, and to do that, fluid intake has to increase. How much fluid should you drink? Better Life has always recommended one-half your body weight in ounces; if you weigh 180 pounds, that’s 90 ounces of water per day. That works out to 2.6 liters and fits within the recommended 2.5-3.0 liters per day.

Not all fluids are equal. Some research has suggested coffee can promote the formation of stones, while other research says coffee reduces stone formation. Grapefruit juice seems to increase risk for unknown reasons, while other citrus foods don’t. If either of these were a regular part of your diet before the stones developed, it might be wise to reduce your intake of those liquids and increase others.

Oxalate Intake
Oxalate is the salt of oxalic acid found in various plants. The problem is that once in the body, it can combine with calcium to form calcium oxalate. This substance can’t be readily processed and can result in kidney stones. Rhubarb, spinach, and chocolate are just some of the foods that can increase plasma oxalate levels. Check out the link in Reference 2 for a more extensive list. The goal is to reduce oxalate intake to less than 50 mg per day.

Salt seems to have a role in the formation of kidney stones, perhaps by increasing the excretion of calcium. As sodium intake increases, so does calcium output, and increasing calcium output increases the risk of forming stones. The goal is to reduce sodium intake to less than two grams (2000 mg) per day.

Protein Intake
Animal protein increases the output of calcium and uric acid--both associated with the formation of kidney stones. Reducing protein intake from animal sources to 80 grams or less is recommended to reduce the formation of stones.

As mentioned earlier, lifestyle recommendations have included reduction of dietary calcium because it’s a significant component of the calcium oxalate stones. However, that recommendation might be changing. In a recent study, researchers examined the reoccurrence of stones in men on a diet lower in sodium and protein but with normal calcium intake (1200 mg) compared with men on a diet with low calcium intake (400 mg) but otherwise unrestricted. After five years, those on the diet low in protein and sodium had less recurrence of kidney stones than those who were on the low-calcium diet. While this is not definitive proof, it has prompted many physicians to modify their thinking about calcium.

Bottom Line
What should you do? First and foremost, talk to your medical specialist. While the evidence indicates that you may not have to follow a low-calcium diet, your physician knows your entire treatment plan, including medications. There may be other reasons for following a low-calcium diet.

Can you use calcium supplements instead of eating more dairy--especially if you’re lactose intolerant? The research isn’t clear--the aforementioned study used only dietary calcium. The only recommendation is that if your doctor allows you to take a calcium supplement, take it with meals because less will be excreted. In reducing your risk of further stone formation, the rest of your lifestyle is more important than the form of calcium you take.

  1. Finkelestein, VA and Goldfarb, DS. Strategies for Preventing Calcium Oxalate Stones. CMAJ 2006; 174(10) 1407-09.


  3. Borghi L et al. Comparison of two diets for the prevention of recurrent stones in idiopathic hypercalciuria. N Engl J Med. 2002 Jan10;346(2):77-84.
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