Diet, but not oral probiotics, effectively reduces urinary oxalate excretion and calcium oxalate supersaturation

Abstract

We examined the effect of a controlled diet and two probiotic preparations on urinary oxalate excretion, a risk factor for calcium oxalate kidney stone formation, in patients with mild hyperoxaluria. Patients were randomized to a placebo, a probiotic, or a synbiotic preparation. This tested whether these probiotic preparations can increase oxalate metabolism in the intestine and/or decrease oxalate absorption from the gut. Patients were maintained on a controlled diet to remove the confounding variable of differing oxalate intake from food. Urinary oxalate excretion and calcium oxalate supersaturation on the controlled diet were significantly lower compared with baseline on a free-choice diet. Neither study preparation reduced urinary oxalate excretion nor calcium oxalate supersaturation. Fecal lactobacilli colony counts increased on both preparations, whereas enterococcal and yeast colony counts were increased on the synbiotic. Total urine volume and the excretion of oxalate and calcium were all strong independent determinants of urinary calcium oxalate supersaturation. Hence, dietary oxalate restriction reduced urinary oxalate excretion, but the tested probiotics did not influence urinary oxalate levels in patients on a restricted oxalate diet. However, this study suggests that dietary oxalate restriction is useful for kidney stone prevention.

Trial registration: ClinicalTrials.gov NCT00587041.

Figure 1

Changes in urinary oxalate on a free-choice diet compared with a controlled metabolic low-oxalate diet. Urine oxalate (a) and CaOx SS (b) values fell on the controlled metabolic diet for the majority of subjects. Other key determinants of SS, including urinary calcium excretion (c), citrate excretion (d), and urine volume (e), did not change. *P<0.001 time zero versus baseline. CaOx, calcium oxalate; SS, supersaturation.

Figure 2

Changes in urine composition while on AKSB and Oxadrop compared with placebo. Urine oxalate (a) and CaOx SS (b) did not change after 4 weeks on either study drug or placebo. CaOx, calcium oxalate; SS, supersaturation. AKSB, Agri-King Synbiotic.

Figure 3

Study design. Baseline urine collections to qualify for the study were collected on a free-choice diet. Patients were placed on a controlled metabolic diet on the first and last week of the study. Two time zero 24-h urine samples were collected on days 5 and 6 of the first week on the controlled metabolic diet (time zero urines) before study preparation was initiated. The probiotic or placebo was then administered for 4 weeks (weeks 2–5). Patients were next placed back on the controlled metabolic diet for the final week of the study (week 5), with two more final urine sample collections on days 5 and 6 of that week (final urines).