03/27/2002 - Articles

Diet Can Cut the Recurrence of Kidney Stones

By: Tufts University

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People who experience recurrent bouts of kidney stones are often told to limit their intake of calcium. That's because calcium is a component of the most common type of kidney stones, called calcium oxalate stones.

But new research indicates that limiting animal protein and salt, instead of calcium, may actually be more effective in preventing calcium oxalate stones. The results are published in a recent issue of The New England Journal of Medicine .

Comparing diets

Researchers in Italy studied 120 men who had a history of kidney stones and randomly divided them into two groups of 60 each. In one group, the men were instructed to eat a low-calcium diet (400 milligrams calcium), by strictly limiting their intake of milk, yogurt, and cheese. The other group was instructed to eat a diet containing a normal amount of calcium (1,200 milligrams), but to keep their intake of animal protein to approximately 52 grams per day (roughly the amount in 2 cups of milk and 5 oz of meat) and their salt intake to 3 grams per day.

Men in both groups were instructed to drink adequate amounts of water (2-3 liters a day) and to limit their consumption of oxalate-containing foods, such as spinach, rhubarb, parsley, and chocolate, because oxalate is another component of kidney stones.

At the end of five years, nearly twice as many men following the low-calcium diet developed kidney stones as those who followed the normal-calcium diet. Twelve of the men in the low-protein, low-salt, normal-calcium group experienced relapses, whereas 23 men in the low-calcium group did.

How the diet may work

The researchers speculate that the reason for the difference in the effects of the two diets has to do with how much oxalate accumulated in the men's urine on each. While a low-calcium diet may be effective in reducing the amount of calcium in the urine, the researchers say this diet may actually increases the amount of oxalate in the urine. This is because less calcium in the intestinal tract allows more absorption of oxalate into the system, which has to be excreted in the urine.

The low-protein, low-salt, normal-calcium diet, however, reduced amounts of both calcium and oxalate in the urine, thereby reducing the risk for formation of calcium oxalate stones.

Further research necessary

While the results of this study are promising, further studies of larger groups of people are needed to confirm them. The researchers point out that their results were only obtained after five years of study, so it is not know whether this diet would be effective in a shorter period. Also, the current study included only men, so it is unclear if the results would have been the same in women.

Advice to consumers

A diet that can prevent the recurrence of kidney stones is an attractive concept, but most consumers would need some diet-planning help to be able to follow the calcium, protein, and salt intake guidelines that produced positive results in this study. Those who suffer from recurrent kidney stones and are currently following a low-calcium diet, however, may want to discuss other diet options with their physician.

Source

Comparison of two diets for the prevention of recurrent stones in idiopathic hypercalciuria.
L. Borghi, T. Schianchi, T. Meschi,  et al., N Eng J Med, 2002, vol. 346, pp. 77--84

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Created on: 03/12/2002
Reviewed on: 03/27/2002

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