Nutrient Energy Intake, Fasting Serum Insulin, and Urinary Oxalate Excretion
Some investigators consider oxalate excretion to be the most critical factor in urine for determining the risk of formation of calcium-oxalate (CaOx) stones. Since urinary oxalate comes largely from endogenous sources, it has been suggested that animal proteins or refined carbohydrates are dietary sources of oxalate precursors in metabolism. However, dietary studies reported from a number of laboratories, including ours, have provided contradictory results. We have re-examined human data, published by Nordenvall et al. (1) and obtained by us in studies of dietary variation in healthy volunteers (2) and parenteral nutrition in cancer patients (3), and found that oxalate excretion (nmol/day.kJ intake) is a function of nutrient energy intake (kJ/day.kg body weight) with y = 488.1x−0.523 (r=0.79, p<0.001, n=152). That is, dietary energy intake explains 60% of the variance in oxalate excretion. Urinary oxalate excretion (mmol/day) can, therefore, be expressed as 0.034 ((total kJ intake/day)/(body weight in kg))0.477. It did not correlate with protein or carbohydrate intake but did correlate with urinary urea excretion (mmol/day), with y=0.184+0.00032x (r=0.47), and with fasting serum insulin (μU/ml), with y=0.164+0.015x (r=0.59). It also correlated with fasting blood glucose and, negatively, with cortisol, but insulin did not correlate with glucose.