Effects of Dietary Chitosan and Genistein on Calcium and Bone Metabolism in Ovariectomized Rats

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Effects of both chitosan, a cationic dietary fiber, and genistein, a soybean phytoestrogen were investigated on bone status and Ca metabolism in ovariectomized (OVX) rats as a model of postmenopausal women.1. Lowering effects of chitosan on the bone mineral density (BMD) and the mechanism by which it decreases BMD; Chitosan caused a significant reduction in BMD and stiffness in femurs and vertebrae of OVX rats fed a low Ca diet for 40 days, as compared to cellulose. There was no remarkable difference in intestinal Ca absorption between chitosan and cellulose, whereas chitosan significantly decreased P absorption. The bone loss in rats fed chitosan was accompanied with a marked increase in urinary Ca excretion and a decrease in serum Ca level, and with a significant increment in serum PIH and 25(CH)_2D_3. Chitosan also significantly increased vitamin D receptor and Ca binding protein D9K mRNAs of the duodenum. These results indicate that dietary chitosan possibly induces the decrease in BMD by enhancing urinary Ca excretion through depressed P absorption, which causes the lowering of serum inorganic P level resulting in the increase in circulating PIH and 1, 25(CH)_2D_3.2. Suppressive effects of genistein dosage and resistance walking on postmenopausal bone loss; Genistein dosage at 5mg/day for 4 weeks to OVX rats significantly lowered the postmenopausal decrease in BMD of femurs, but not of vertebrae. For complementing the preventive function of genistein to vertebrae loss, the effects of different moderate exercises were evaluated. Resistance exercise constituted of 1-min walking interspersed with 1-min rest with 100g weight on the back successively reduced the postmenopausal BMD decrease in vertebrae, but not in the case of ordinary walking. The combined treatment of genistein and resistance walking acted independently to the prevention of postmenopausal bone loss.