Bioavailability of zinc to rats from soybeans and casein as affected by protein source and length of adaptation

Abstract

The effect of basal diet and length of adaptation on bioavailability of zinc from soybeans hydroponically grown and intrinsically labeled with 65Zn and casein extrinsically labeled with 65Zn was investigated. Thirty-day-old male rats (Sprague Dawley) were adapted to soy or casein basal diets for 8,32 or 56 days. At the end of each adaptation period, a soy or casein test meal was fed to rats adapted to both soy and casein basal diets. Whole body retention of 65Zn from the soy test meal remained constant over the entire adaptation period in rats adapted to the soy basal diet, suggesting that adaptation or lower zinc status offset the natural decrease in absorption with age. In contrast, retention of 65Zn from both the casein and soy test meals in rats adapted to the casein basal diet dropped over the adaptation period as zinc status and age of the rats increased. To the extent that the rat is a good model of human zinc metabolism, this study suggests that adaptation and enhanced absorption due to marginal zinc status may prevent zinc deficiencies in vegetarian populations.