Influence of the Dietary Protein Level on the Magnesium Requirement

The effect of the dietary protein intake upon the magnesium requirement of the chick and the rat was investigated. When magnesium was limiting, an increase in the dietary protein level retarded growth and increased mortality in the chick. Similarly, the higher level of protein restricted weight gain in the rat at a low level of magnesium intake. A classic symptom of magnesium deficiency, vasodilatation, was observed in the rats fed 36% protein and 200 ppm magnesium, a level of this mineral which is normally considered adequate. A balance study in the rat failed to produce evidence of an effect of dietary protein on apparent absorption although urinary excretion of magnesium was increased with the higher protein diet. Urinary calcium was elevated following an increase in either dietary protein or magnesium. Analyses of rat liver and kidneys showed that differences in the magnesium content of the former, but not the latter, occurred at different intakes of magnesium so long as appreciable growth was achieved. Kidney calcium was increased markedly by a decrease in dietary magnesium. Changes in total serum protein and in the urinary excretion of leucine, isoleucine and valine were observed which were suggestive of an important role for magnesium in protein and amino acid metabolism.