Different effects of oral glycine and methionine on urinary lithogenic substances.

Nine male healthy volunteers were examined during a control period, during an oral glycine load (45 g/day, 600 mmol) and oral methionine (6 g/day, 40 mmol). Glycine caused a significant increase of urinary oxalate above baseline (from 644 to 797 mumol/day) without change in calciuria (4.74 vs 4.84 mmol/day). In contrast methionine caused no change of oxaluria, but a significant increase in calciuria (from 4.74 to 6.9 mmol/day). Alterations of lithogenic ions in urine after protein ingestion are mediated by different amino acids. The particular lithogenic risk of animal protein may be related to its high methionine/cystine and glycine content.