Bioavailability of Zinc from Defattd Soy Flour, Soy Hulls and Whole Eggs As Determined by Intrinsic and Extrinsic Labeling Techniques

Abstract

Bioavailability of zinc from diets prepared from intrinsically and extrinsically labeled autoclaved, defatted soy flour and scrambled, freeze-dried egg was investigated in male rats marginally depleted in zinc. In one study, retention of zinc from intrinsically labeled soybean flour (73%) was significantly less than from ⁶⁵ZnCl₂ extrinsically added to a soy flour-based diet (80%). Zinc from intrinsically labeled soybean hulls and from soy flour diets containing 10% soybean hulls extrinsically labeled with ⁶⁵ZnCl₂ was as available as the zinc from the extrinsically labeled soy flour diet. In a second study, extrinsic and intrinsic labeling techniques gave a similar assessment of bioavailability of zinc from egg- and soy flour-based diets when extrinsic labeling was accomplished by thoroughly mixing ⁶⁵ZnCl₂ with the protein source prior to incorporation into the diet. Absorption of ⁶⁵Zn was greater from egg diets than from soy flour diets and of intermediate value from mixed soy flour and egg (50:50, wt/wt) diets regardless of which protein source was labeled, indicating that the zinc entered a common pool.