High animal
protein intake is a risk factor for
calcium oxalate stone disease. The effect of
dietary protein on the urinary excretion of
calcium,
acid and
citrate is well established. However, its effect on
oxalate excretion is unclear, due in part to an inadequate control of dietary
oxalate intake in previous studies. This relationship warrants clarification due to the proposed important role of the metabolism of
amino acids in endogenous
oxalate synthesis. In this study, 11 normal subjects consumed controlled
oxalate diets containing 0.6, 1.2 and 1.8
g protein/kg
body weight/day. The analysis of 24 h urine collections confirmed that as
protein intake increased, urinary
calcium and
glycolate increased and urinary pH and
citrate decreased. The increased
glycolate excretion was due in part to an increased
hydroxyproline, but not
glycolate consumption. Total daily urinary
oxalate excretion did not change. When indexed to
creatinine there was a small but significant decrease in
oxalate excretion. This is most likely due to hyperfiltration. These results indicate that as
dietary protein intake increases, the catabolism of diet-derived
amino acids is not associated with an increased endogenous
oxalate synthesis in normal subjects.