Dietary protein, fat, and minerals in nephrocalcinosis in female rats

Young female rats fed semipurified diets containing casein or a soy protein isolate had extensive nephrocalcinosis at the junction between the outer and inner stripe of the outer medullary zone after 5 wk on the diets, whereas rats fed a diet containing a lactalbumin concentrate did not. Although the percentages of actual protein and of total ash were similar in all three diets, the concentrations of individual minerals were not, owing to methods used in isolating the proteins. Comparison of the individual mineral contents of these diets with those in other laboratories as compiled from the literature suggested that factors other than minerals, including protein, are also implicated. Dietary fat appeared to be another such factor in a series of experiments in which saturated medium-chain triglycerides and corn oil were included in diets containing soy protein isolate. Although these diets had identical mineral compositions, the rats fed medium-chain triglycerides had less severe lesions.