Nutrition and magnesium absorption

The influence of various nutrients present in dairy products and soybean-based products on absorption of magnesium has been investigated. The studies demonstrate that soybean protein versus casein lowers apparent magnesium absorption in rats through its phytate component. However, true magnesium absorption was neither affected by soybean protein in the diet nor by supplemental phytate. The inhibitory influence of soybean protein and phytate on apparent magnesium absorption was found to be caused by stimulation of fecal excretion of endogenous magnesium. The loss of magnesium was compensated for by depressed urinary magnesium excretion so that whole-body magnesium retention was left unchanged. Lactose in the diet raised both apparent and true magnesium absorption in rats. Phytate and lactose, as intrinsic component of milk and soybean beverage still exerted their influence on apparent magnesium absorption in rats. The stimulatory effect of lactose is most likely due to the lactase-deficiency of these animals. Microbial fermentation of lactose in the intestine may have caused the observed decrease in intestinal pH. This might result in increased magnesium solubility in the ileal lumen, which in turn stimulates magnesium absorption. The concentration of soluble magnesium in the intestinal lumen, at least at low concentrations, is the major determinant of the amount of magnesium absorbed. In lactose-tolerant humans possessing lactase in the intestine, lactose did not affect magnesium absorption. Increasing intakes of calcium may reduce apparent magnesium absorption, depending on the phosphate: magnesium ratio in the diet. High ratios favor the formation of an insoluble magnesium-calcium- phosphate complex in the intestine after consumption of extra calcium, so that magnesium absorption is impaired. This mechanism speaks against a common mechanism for transport of magnesium and calcium across the intestinal mucosa.