Theoretical and laboratory investigations of the effects of hydroxyproline ingestion on the metabolic and physicochemical risk factors for calcium oxalate kidney stone formation in a small group of healthy subjects

Rodgers A, Cele P, Ravenscroft N, Edmonds-Smith C, Jackson G · International Urology and Nephrology

The counterweight to the Wake Forest result, at the same 30 g gelatin dose. Urinary glycolate rose significantly, confirming the hydroxyproline is being metabolised — but oxalate excretion and the relative supersaturation of calcium oxalate did not change, and ionised calcium fell as urine pH rose. The authors attribute the divergence to the mixed-ancestry composition of their group and suggest metabolic pathway preference differs between individuals.

Population

Three healthy white and two healthy black males, Cape Town

Intervention

30 g gelatin daily for 3 days, 24-hour urines at baseline and after

Limitations

Five men and three days, which is too small to overturn a controlled crossover and is described by its own authors as exploratory. No stone formers were studied. The glycolate rise without an oxalate rise is unexplained.