Q. A 24-year-old man comes to the physician complaining of repeated episodes of severe abdominal pain that he describes as "coming and going in waves." His medical history is unremarkable, except for similar episodes of pain over the past two years. During one of these episodes, a stone was removed from his urinary tract and analyzed, revealing it to be primarily composed of cystine. Which of the following measures will be most effective in preventing the recurrence of his symptoms?