Bioavailability of Zinc from a Diet Based on Isolated Soy Protein: Application in Young Men of the Stable Isotope Tracer, 70Zn

With the aid of the stable isotope, 70Zn, as a tracer and neutron activation analysis, a combination of extrinsic labeling of meals and fecal monitoring of isotope excretion was used as a safe and noninvasive approach for assessing the effects of the vegetable (soy) and animal (milk, beef) proteins on the absorption of zinc in healthy, adult human volunteers. A known amount of 70Zn was added as ZnCl2, to six consecutive meals over a 2-day period during which either one of three isonitrogenous liquid formulas (skim milk; soy isolate; or a 50:50 mixture) or one of two bologna sausages (soy isolate or beef) were given. The mean absorption of 70Zn from milk, soy and soy/milk was 41 ± 4, 34 ± 4, and 41 ± 7% (mean ± sem), respectively, the presence of soy protein having no effect on absorption of the extrinsic label. For beef bologna and soy bologna, fractional absorption of the 70Zn tracer was 41 ± 4 and 30 ± 3%, respectively. Beef might favor absorption of extrinsic zinc. The kinetics of isotope excretion, pooling procedures for stool samples and the utility of fecal markers were also evaluated. zinc soy protein bioavailability stable isotopes neutron activation analysis