Dietary Fructose as Compared to Glucose and Starch Increases the Calcium Content of Kidney of Magnesium-Deficient Rats

Abstract

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.

Fructose consumption and the risk of kidney stones

“…Rats fed a magnesium-deficient, fructoserich diet for 4 weeks had eightfold greater levels of nephrocalcinosis than rats with magnesium-deficient diets with energy derived from glucose or starch. 8 The nephrocalcinosis in the magnesium-deficient fructose diet was accompanied by hypercalciuria and consisted of calcium phosphate, rather than calcium oxalate, deposition. 7 The latter is an intriguing finding given that the initial phase of calcium oxalate stones may be interstitial deposits of calcium phosphate.…”

“…Rats fed high-fructose diets have higher urinary calcium excretion and an eightfold increase in nephrocalcinosis compared to rats fed high-starch diets. 7,8 A study of calcium and phosphorus balance in healthy men consuming controlled diets demonstrated higher urinary losses of calcium as a percentage of calcium intake on a high-fructose versus high-starch diet. 9 In another study on human, intravenous infusion of fructose increased urinary oxalate excretion by 60% compared to glucose infusion.…”

“…10 Of note, the effect of fructose intake on calcium balance and urinary oxalate excretion may vary depending on the intake of magnesium and vitamin B 6 , respectively. [7][8][9]11 Fructose intake may also increase insulin resistance, which is associated with low urinary pH, 12 a major risk factor for uric acid kidney stones. In addition, fructose is the only carbohydrate known to increase the production of uric acid.…”

Evolution of Mg Deficiency in Rats

“…The increase in ash content in kidney (ta ble 4) caused by dietary Mg deficiency has been convincingly shown to result from the formation of calcium phosphate and calcium oxalate deposits [4,15,16]. This appears to be dependent on the Mg/Ca ratio in the renal tubule, low ratios being associated with an increased risk of kidney stone formation [17].…”

Update on the medical management of stone disease

“…Experimental studies on rats have shown that high fructose consumption increases urinary calcium excretion and induces nephrocalcinosis [22,23]. Additionally, healthy men given high-fructose diets or an intravenous infusion of fructose developed hypercalciuria, hyperoxaluria, and hyperuricosuria [24,25].…”