Dietary fructose as compared to glucose and starch increases the calcium content of kidney of magnesium-deficient rats.

The effects of feeding diets containing fructose, glucose or starch with or without added magnesium (Mg) on tissue levels of calcium (Ca) in weanling rats were investigated. Rats were fed their respective diet for 4 wk and then fasted overnight. After decapitation, blood was immediately collected, and liver, kidney and heart were removed to determine their Mg and Ca content. Relative kidney and liver weights were greatest in the rats fed the fructose diet. Hypomagnesemia was observed in all animals fed a Mg-deficient diet regardless of carbohydrate source (1.71 vs. 2.27 mg Mg/dl plasma for Mg-deficient vs. Mg-adequate groups, respectively). Among Mg-deficient groups, starch-fed rats had the highest level of plasma Mg, while fructose-fed rats had the highest level of kidney Mg. Although plasma and liver Ca levels were not significantly different among the groups, Ca content of the kidney and heart was greatest in animals fed a Mg-deficient diet with fructose. This was especially evident in the Ca content of the kidney, which was 8- to 9-fold greater than that of all other experimental groups. The results of the present study demonstrate the presence of a synergistic interaction between fructose and Mg deficiency that increases Ca levels in certain soft tissues, especially the kidney.