Nutritional Availability of Zinc Contained in Phytin in Rats with Adequate and Low Zinc Status

抄録

In cereals and legumes, phytic acid is present as phytin bound with magnesium and zinc. In this study, the nutritional availability of zinc-containing phytin as a zinc source was compared between rats with an adequate zinc status and those with a low zinc status. Twenty-four male 4-week-old Wistar rats were divided into four groups (AZ, AZP, LZ, and LZP): the AZ group was fed a basal AIN93G diet containing adequate amounts of zinc (zinc concentration, 35.6 mg/kg), the AZP group was fed a phytin-supplemented basal diet (40.7 mg/kg), the LZ group was fed a low zinc diet (5.0 mg/kg), and the LZP group was fed a phytin-supplemented low zinc diet (10.2 mg/kg) for 4 weeks. The LZ group showed significantly lower feed intake, body weight, organ weights, organ and serum zinc concentrations, and serum alkaline phosphatase activity than the AZ group, indicating that they were moderately zinc-deficient. In the LZP group fed the phytin-supplemented low zinc diet, the apparent absorption rate of zinc was lower than in the LZ group, but the amount of apparent absorption was higher than in the LZ group, and feed intake, body weight, and organ weights recovered to the same levels as in the AZ group. Organ and serum zinc levels in the LZP group were also significantly higher than in the LZ group. On the other hand, although the AZP group consumed more zinc than the AZ group, they excreted markedly more zinc in their feces, and the apparent amount of zinc absorption was significantly lower than that of the AZ group. In addition, serum and femoral zinc concentrations and serum alkaline phosphatase activity were significantly lower in the AZP group than in the AZ group. These results indicate that zinc-containing phytin is utilized as a zinc source in the presence of a low zinc status, but inhibits zinc utilization when the zinc status is adequate.