Dietary fructose vs. glucose stimulates nephrocalcinogenesis in female rats

The effect of dietary fructose vs. glucose on kidney calcification (nephrocalcinosis) was studied in female rats. Fructose or glucose was incorporated into purified diets formulated either according to the nutrient requirements of rats or made nephrocalcinogenic by the addition of phosphorus (19.4 instead of 12.9 mmol/100 g diet) or by restriction of magnesium (0.8 instead of 1.6 mmol/100 g diet). Irrespective of the background composition of the diet, fructose consistently produced higher kidney calcium concentrations than did glucose. Fructose also raised kidney weight, expressed either as wet weight relative to body weight or as absolute dry weight; this greater kidney weight was not explained by the extra calcium. Fructose generally induced greater urinary concentrations of phosphorus and magnesium and lowered urinary pH compared with glucose. The greater urinary phosphorus concentrations in rats fed fructose may be responsible for the nephrocalcinogenic activity of this monosaccharide. Fructose stimulated the absorption of phosphorus and magnesium, which explains the higher concentrations of these minerals in the urine.