Effects of lemon–tomato juice consumption on crystal formation in the urine of patients with calcium oxalate stones: A randomized crossover clinical trial

BACKGROUND: Dietary 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 METHODS: The 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. RESULTS: There 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). CONCLUSIONS: The 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.