General and dietary oxalate restriction advice reduces urinary oxalate in the stone clinic setting

Abstract

Background: Idiopathic hyperoxaluria is a risk factor for developing calcium oxalate nephrolithiasis. Dietary oxalate’s effect on urinary oxalate is not well  studied. The aim of this study is to assess the effect of advice focused on reducing dietary oxalate in a cohort of idiopathic hyperoxaluric patients.

Methods: Patients referred to the Groote Schuur Hospital Stone Clinic from 2015 to 2017 were considered eligible, if they were an idiopathic  hyperoxaluric stone former, excreting > 40 mg/d of urinary oxalate on a pre-intervention 24-hour stone study urinalysis. Patients were asked to adhere to  a diet sheet which included general stone prevention advice (low salt diet, increased fluid intake and moderate protein intake) and specific low oxalate  diet advice. A post-intervention 24-hour urinalysis was performed at six weeks.

Results: Nineteen patients had hyperoxaluria (eight men and 11 women) with a mean age of 49 years (range 25–76 years). The mean BMI of the group  was 28.4 kg/m2 (17.4–50). All patients had mean number of 1.9 range prior stone episodes (range 1–6 stone episodes). Fourteen (14/19) patients  completed the study. The mean pre-dietary advice urinary oxalate was 53.2 mg/24 hours (n = 14), SD while the post-intervention was 29.6 mg/24 hours  SD (p = 0.0002). Only 3/14 patients who completed the assessment failed to normalise their urinary oxalate on the diet.

Conclusion: In the stone clinic setting, general advice of low salt diet, increased water intake, moderate protein intake and specific oxalate restriction can  significantly reduce oxalate excretion in hyperoxaluric stone formers. Sustained reduction of oxalate excretion and longitudinal clinical benefit are worthy  of study in larger cohorts.