Calcium metabolism in young undernourished rats fed diets differing in protein and calcium content.

The purpose of this study was to examine the relationship between protein intake and calcium metabolism in young rats. Just weaned rats were fed diets with different protein content, combined with normal and low-calcium intake. The food consumption and bodyweight gain were low but equal in all experimental groups. After five weeks on the experimental diets 40 animals were given an intraperitoneal injection of, 45Ca, 40Ca, and 45Ca in urine and feces were determined for three consecutive days, respectively. The high-protein diets exerted a strong calciuric effect in animals fed both a normal- and low-calcium diet, but there was no significant influence of the protein intake on the resorption of calcium. A high-protein content of the diet was associated with a significant although moderate increase in bone mass; paradoxically, the accretion rate was not influenced by the protein content of the diet. Despite conditions associated with growth, dietary protein does not alter the resorption or accretion of calcium, but does significantly influence the excretion of calcium.