Stratum 1: Hypocitraturia (urinary citrate excretion >320 mg/24 h) Stratum 2: Normocitraturia (urinary citrate excretion <320 mg/24 h) Within each stratum, patients will be randomized on a 1:1 basis to two-year treatment with lemon juice supplemented to standard recommended diet or to standard diet alone. All patients in the hypocitraturic stratum will also be prescribed potassium citrate 2g twice daily. Due to the Prospective, Randomized, Open, Blind Endpoint (PROBE) design of the study, patients and physicians in charge of patient care and monitoring will be aware of patient treatment, while all the Investigators involved in data handling and analyses will be blinded to patient treatment allocation.