Bioavailability in humans of zinc from beef: Intrinsic vs extrinsic labels

Beef is a concentrated source of zinc. However, the bioavailability of Zn from beef has not been clearly established. It is also unclear whether there is a difference in absorption between intrinsic and extrinsic Zn. To address these questions, a calf was labeled with ⁶⁵ZnCl₂ and the meat was used as a source of intrinsically labeled beef. Twelve subjects were given a meal containing 100 g beef labeled either intrinsically or extrinsically with ⁶⁵ZnCl₂. Gamma-ray emissions, as determined by whole-body counting, were used to calculate Zn absorption. Absorption values were 20.9 ± 5.5% from the extrinsic meal and 26.4 ± 10.6% from the intrinsic meal, a difference that was not statistically significant (p > 0.05). Zn absorption was thus much less than the 40% assumed in establishing the 1980 Recommended Dietary Allowance for Zn. These results also indicate that extrinsic labels of Zn are valid markers of zinc absorption in beef.