Meal protein and zinc levels interact to influence zinc retention by the rat

Abstract

The relationship between the effect of egg white protein and zinc in a meal on zinc retention was examined by feeding test meals labeled with Zn-65 to rats and monitoring retention of radioactivity with a whole body counter. Corrected retention (an estimate of absorption) was determined by extrapolating to zero time the semilogarithmic plot of Zn-65 retention between 5 and 26 days after the meal. Test meals contained fixed amounts of sucrose, cornstarch, corn oil, and variable amounts of egg white and zinc chloride. Fractional zinc retention was reduced by increasing the usual dietary zinc intake or zinc in the meal, and was enhanced by increasing protein in the meal. Meal zinc and protein interacted, such that with more zinc in the meal, more protein was needed to observe enhanced zinc retention. Enhancement of zinc retention by protein was not linear with the amount of protein and was not related to the protein to zinc ratio in the meal. The interaction was similar whether rats were accustomed to diets containing 14 or 37 mg zinc/kg. These data indicate that zinc absorption is affected by an interaction between the protein and zinc content of a meal, and the dose-response relationship between the amount of zinc consumed and the amount retained may be amplified by a moderate amount of protein.