Bioavailability of magnesium contained in roasted and ground soybean (kinako) as evaluated by serum and bone magnesium contents, kidney calcification, and magnesium absorption.

The bioavailability of roasted and ground soybean (kinako) magnesium (Mg) in Fischer 344 strain male rats with respect to serum Mg level, bone Mg contents, kidney calcification, and Mg absorption was evaluated. Four-week-old male rats were divided into four groups of six rats each. The four groups were the control (20SC), Mg-deficient diet (1/3 Mg20SC), 20SCK diet, and 20SCDK diet. The 20SCK and 20SCDK diets were prepared to contain amounts of Mg equal to that in the 20SC diet with kinako or defatted kinako as the Mg source, respectively. After a 4-week experimental period, rats were decapitated and blood serum, right femur, and right kidney were collected, and Mg, calcium (Ca), and phosphorus (P) concentration in those tissues were determined. The Mg balance was also investigated. The serum Mg concentration in the 1/3 Mg20SC group was half the level in the 20SC group, and the serum Ca concentration was higher than in the 20SC group, indicating apparent hypercalcemia. Serum Mg and Ca concentrations in the 20SCK and 20SCDK groups did not significantly differ from those in the 20SC group. Femur Mg concentration in the 1/3 Mg20SC group was lower than in the 20SC group. Femur Mg concentrations in the 20SCK and 20SCDK groups were lower than in the 20SC group, but significantly higher than in the 1/3 Mg20SC group. The kidney Ca concentrations in the 20SCK and 20SCDK groups were significantly higher than those in the 20SC and 1/3 Mg20SC groups, and there was also kidney calcification. These results indicated that kinako and defatted kinako Mg were used effectively as a serum and femur Mg source, but that kinako and defatted kinako carry a risk of kidney calcification when used as the only Mg source.