ZINC-ABSORPTION IN WOMEN - COMPARISON OF INTRINSIC AND EXTRINSIC STABLE-ISOTOPE LABELS

Fractional absorption of extrinsic and intrinsic zinc from milk-based formulated diets was measured in 10 young women by using a simultaneous triple-isotope method based on fecal monitoring of unabsorbed enriched stable-isotope labels. Zinc intake was held nearly constant (xBAR zinc intake = 1.48-mu-mol.kg body wt-1.d-1) throughout the 18-d controlled feeding phase of the study by addition of extrinsic Zn-64 to all formula feedings, with substitution of the extrinsic Zn-67 label for some of the Zn-64 when formula intrinsically labeled with Zn-70 was given. Fractional absorption values of intrinsic and extrinsic zinc labels, 0.267 +/- 0.092 (xBAR +/- SD) and 0.282 +/- 0.086, respectively, were highly correlated (r = 0.83, P < 0.05) and did not differ significantly. The ratio of fractional absorption of the extrinsic to that of the intrinsic label, 1.08 +/- 0.20 (xBAR +/- SD), was not significantly different from unity. The results show that extrinsic labeling by use of enriched stable isotopes is a valid means of determining zinc absorption from milk-based diets in adult humans.