Background Patients with idiopathic calcium oxalate stones are advised to consume a low-oxalate diet to prevent recurrence. In this study, on patients with calcium oxalate stones we have attempted to determine the effect of calcium content of diet on the formation of calcium oxalate crystals in urine by in vitro supersaturation study of fresh postprandial urine samples and observing the morphology of the crystals formed using polarized optical microscopy. Methods The trial was conducted as a prospective interventional randomised crossover clinical trial in a repeated measures design. Sixty patients with calcium oxalate stones and no metabolic abnormalities in urine treated by lithotripsy at a tertiary care centre during the period May 2016 to May 2019 were recruited. Following a 14 h overnight fasting, urine samples were collected after providing the patient with either a low- or high-calcium meal for breakfast followed four hours later, by high-oxalate meal for lunch. Urine was tested for multiple parameters including urine pH, specific gravity, calcium/creatinine ratio and supersaturation of urine with sodium oxalate followed by optical density measurement by spectrophotometry and microscopic analysis of crystals formed. Results Optical density values and calcium/creatinine ratio of urine samples obtained after high-calcium meal are significantly higher than in corresponding sample obtained after low-calcium meal (p < 0.001). These findings were reflected in the morphology of formed crystals in their size, shape and number. When urinary calcium levels were low, no crystals were formed during supersaturation study of postprandial urine samples following a high-oxalate diet. Conclusions High calcium content in diet significantly contributes to kidney stone formation. There is a lower risk of kidney stone formation with a low-calcium meal even on consumption of a high-oxalate diet.

BackgroundDietary supplementation with citrate-containing juices may serve as an effective alternative to potassium citrate therapy for preventing calcium oxalate stone recurrence. This study was performed to evaluate whether consumption of lemon–tomato juice can decrease the tendency for stone formation in the urine of calcium oxalate stone formers.Materials and methodsThe study was conducted as a prospective interventional randomized crossover clinical trial with a repeated-measures design. Twenty-two patients with calcium oxalate stones and no metabolic abnormalities in the urine treated with lithotripsy at a tertiary care center from August 2017 to July 2018 were recruited. After a 14-hour overnight fasting, urine samples were collected after the patients consumed either milk only or milk and lemon–tomato juice. Their urine was tested for multiple parameters, including urine pH, specific gravity, calcium–creatinine ratio, and supersaturation with sodium oxalate, followed by optical density measurement via spectrophotometry.ResultsThere were no significant differences in the background characteristics between the 2 groups. The optical density of the urine samples obtained after consumption of milk only was significantly higher than that after consumption of milk and lemon–tomato juice (mean = 0.131 for milk only vs. 0.053 for milk and lemon–tomato juice, p < 0.001). The urine calcium–creatinine ratio was similar between the groups (mean = 0.141 for milk only vs. 0.076 for milk and lemon–tomato juice, p = 0.019).ConclusionsThe addition of lemon–tomato juice as a source of citrate in the diet significantly decreases the established risk factors for calcium oxalate stone formation in patients. This study was prospectively registered at CTRI under number CTRI/2017/04/008312 on April 7, 2017.

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