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 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
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)
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
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.
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.
- Finkelestein, VA and Goldfarb, DS. Strategies for Preventing Calcium
Oxalate Stones. CMAJ 2006; 174(10) 1407-09.
- Borghi L et al. Comparison of two diets for the prevention of
recurrent stones in idiopathic hypercalciuria. N Engl J Med. 2002