Simple dietary advice targeting five urinary parameters reduces urinary supersaturation in idiopathic calcium oxalate stone formers

Among 208 kidney stone patients referred within 2 years, 75 patients (66 men, nine women) with truly idiopathic calcium oxalate stones (ICSF) were recruited. Dietary advice (DA) aimed at (1) urine dilution, (2) reduced crystallization promotion (lowering oxalate), and (3) increased crystallization inhibition (increasing citrate). We recommended higher intakes of fluid and calcium with meals/snacks (reducing intestinal oxalate absorption) as well as increased alkali and reduced meat protein (acid) for increasing urinary citrate. The intended effects of DA were elevations in urine volume, calcium (U-Ca) and citrate (U-Cit) as well as reductions in oxalate (U-Ox) and uric acid (U-UA). We retrospectively calculated an adherence score (AS), awarding + 1 point for parameters altered in the intended direction and − 1 point for opposite changes. Calcium oxalate supersaturation (CaOx-SS) was calculated using Tiselius’ AP(CaOx) index EQ. DA induced changes (all p < 0.0001) in urine volume (2057 ± 79 vs. 2573 ± 71 ml/day) and U-Ca (5.49 ± 0.24 vs. 7.98 ± 0.38 mmol/day) as well as in U-Ox (0.34 ± 0.01 vs. 0.26 ± 0.01 mmol/day) and U-UA (3.48 ± 0.12 vs. 3.13 ± 0.10 mmol/day). U-Cit only tendentially increased (3.07 ± 0.17 vs. 3.36 ± 0.23 mmol/day, p = 0.06). DA induced a 21.5% drop in AP(CaOx) index, from 0.93 ± 0.05 to 0.73 ± 0.05 (p = 0.0005). Decreases in CaOx-SS correlated with AS (R = 0.448, p < 0.0005), and highest AS (+ 5) always indicated lowering of CaOx-SS. Thus, simple DA can reduce CaOx-SS which may be monitored by AS.