120 men with recurrent calcium oxalate stones and hypercalciuria were enrolled in a five-year randomised trial . They consumed either a diet containing a normal amount of calcium (30 mmol/day) but reduced amounts of animal protein (52g per day) and salt (50 mmol of sodium chloride per day)(group A) or a traditional low-calcium diet that contained 10 mmol of calcium per day (group B). At five years, 12 of the 60 men in group A, but 23 of the 60 men in group B had had relapses of kidney stones (relative risk 0.49, 95% CI 0.24 to 0.98).
Comment: The quality of evidence is downgraded by sparse data and potential for reporting bias (no thorough literature search was performed).