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Kidney Stone Diets Compared

A diet with ample calcium, and reduced animal protein and salt is superior to a low-calcium diet for the prevention of recurrent kidney stones.

This is the finding of a five-year comparison of the effects of two different diets for the prevention of recurrent stones in men with idiopathic hypercalciuria.

Although a low-calcium diet is recommended to prevent recurrent stones in patients with idiopathic hypercalciuria, long-term data on the efficacy of a low-calcium diet have been lacking. Recently, the efficacy of a low-calcium diet has been questioned, and greater emphasis has been placed on reducing the intake of animal protein and salt.

In this randomised trial, researchers compared the effects of two diets in 120 men with recurrent calcium oxalate stones and hypercalciuria.

Sixty men were assigned to a diet containing a normal amount of calcium (30 mmol per day) but reduced amounts of animal protein (52 g per day) and salt (50 mmol of sodium chloride per day).

The other 60 men were assigned to the traditional low-calcium diet, which contained 10 mmol of calcium per day.

At the five-year mark, 12 of the 60 men on the normal-calcium, low-animal-protein, low-salt diet, and 23 of the 60 men on the low-calcium diet had had relapses.

Unadjusted relative risk of a recurrence for the group on the first diet versus those on the second diet was 0.49.

In follow-up, urinary calcium levels dropped significantly in both groups by approximately 170 mg per day (4.2 mmol per day).

However, urinary oxalate excretion increased in the men on the low-calcium diet but decreased in those on the normal-calcium, low-animal-protein, low-salt diet.

Thus, in men with recurrent calcium oxalate stones and hypercalciuria, restricted intake of animal protein and salt, combined with a normal calcium intake, provides greater protection than the traditional low-calcium diet, these researchers conclude.

Kidney stones have a lifetime incidence of up to 13 percent in North America. In the United States alone, the stones were responsible for an estimated 1.32 million visits to doctors in 1995 and for US$1.83 billion in health care costs in 1993.

In at least 70 percent of cases, the stones consist of calcium oxalate crystals, often with calcium phosphate or sodium urate.

Once a stone forms, there is approximately a 50 percent probability that a second stone will form within five to seven years in the absence of treatment.

Loris Borghi and colleagues from the Departments of Clinical Sciences and Internal Medicine and Nephrology, University of Parma, Parma, Italy did this work.
N Engl J Med 2002;346:77-84. "Comparison of Two Diets for the Prevention of Recurrent Stones in Idiopathic Hypercalciuria"

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