Bioavailability of zinc to rats as affected by protein source and previous dietary intake

The bioavailability of zinc from defatted soy flour, dried chicken meat or mixed (50:50 dry weight basis) soy flour and chicken meat included in egg white-based diets was investigated in rats. Following a 6-d experimental diet (9 ppm Zn) feeding period, marginally zinc-depleted weanling rats were fed a test meal, identical in composition to the experimental diet except that the protein source was labeled either intrinsically or extrinsically with 65Zn. Retention of 65Zn from the chicken test meal was significantly higher than that from the soy test meal. Retention of 65Zn from the mixed soy/chicken test meal was midway between the retention values for either protein alone regardless of which protein source was labeled. Intrinsic and extrinsic labeling techniques resulted in similar assessment of zinc bioavailability. Additionally, the influence of previous dietary protein source on zinc retention from a soy test meal was investigated. Retention of 65Zn from an intrinsically labeled soy test meal was higher in rats adapted to chicken protein than in rats adapted to soy protein. The levels of tibia zinc and tibia 65Zn were associated with whole-body retention of 65Zn.