The influence of diet on urinary risk factors for stones in healthy subjects and idiopathic renal calcium stone formers

The daily intake of 103 recurrent idiopathic calcium stone formers and 146 controls was assessed by means of a computer-assisted 24-h dietary record. Timed 24-h urine samples were collected over the same period to assess the relationship between dietary intake of nutrients and urinary risk factors for calcium stones. After standardisation for sex, age and social status a total of 128 subjects underwent final statistical analysis; 64 renal stone formers and 64 controls. Significant increases in the consumption of animal and vegetable protein and purine were identified as the nutritional factors that distinguished renal stone formers from controls. As expected, the daily urinary excretion of calcium and oxalate was higher and the daily urinary excretion of citrate was lower in stone formers than in controls. No difference with respect to daily urinary uric acid excretion was recorded. Daily urinary excretion of calcium was correlated to dietary protein intake while daily urinary oxalate was correlated to dietary vitamin C intake. It was concluded that renal stone formers could be predisposed to stones because of their dietary patterns. A link between the protein content of the diet and urinary calcium was confirmed, but dietary animal protein had a minimal effect on oxalate excretion.