Diet, fluid, or supplements for secondary prevention of nephrolithiasis: a systematic review and meta-analysis of randomized trials.

CONTEXT: Although numerous trials have evaluated efficacy of diet, fluid, or supplement interventions for secondary prevention of nephrolithiasis, few are included in previous systematic reviews or referenced in recent nephrolithiasis management guidelines.

OBJECTIVE: To determine efficacy and safety of diet, fluid, or supplement interventions for secondary prevention of nephrolithiasis.

EVIDENCE ACQUISITION: Systematic review and meta-analysis of trials published January 1950 to March 2008. Sources included Medline and bibliographies of retrieved articles. Eligible trials included adults with a history of nephrolithiasis; compared diet, fluids, or supplements with control; compared relevant outcomes between randomized groups (eg, stone recurrence); had > or = 3 mo follow-up; and were published in the English language. Data were extracted on participant and trial characteristics, including study methodologic quality.

EVIDENCE SYNTHESIS: Eight trials were eligible (n=1855 participants). Study quality was mixed. In two trials, water intake > 2 l/d or fluids to achieve urine output > 2.5 l/d reduced stone recurrence (relative risk: 0.39; 95% confidence interval: 0.19-0.80). In one trial, fewer high soft drink consumers assigned to reduced soft drink intake had renal colic than controls (34% vs 41%, p=0.023). Content and results of multicomponent dietary interventions were heterogeneous; in one trial, fewer participants assigned increased dietary calcium, low animal protein, and low sodium had stone recurrence versus controls (20% vs 38%, p=0.03), while in another trial, more participants assigned diets that included low animal protein, high fruit and fiber, and low purine had recurrent stones than controls (30% vs 4%, p=0.004). No trials examined the independent effect of altering dietary calcium, sodium, animal protein, fruit and fiber, purine, oxalate, or potassium. Two trials showed no benefit of supplements over control treatment. Adverse event reporting was poor.

CONCLUSIONS: High fluid intake decreased risk of recurrent nephrolithiasis. Reduced soft drink intake lowered risk in patients with high baseline soft drink consumption. Data for other dietary interventions were inconclusive, although limited data suggest possible benefit from dietary calcium.