INFLUENCE OF A MEAL AND INCREMENTAL DOSES OF ZINC ON CHANGES IN ZINC-ABSORPTION

The objective of this study was to determine the effect of increasing quantities of zinc, administered with and without a meal, on zinc abso rption. Fractional absorption of incremental quantities of zinc in fou r normal adults was determined by measuring fecal excretion of unabsor bed isotope on 3 consecutive days by using three different stable isot opes of zinc (Zn-67, Zn-68, and Zn-70). Isotopes were administered in the post-absorptive state and, on a subsequent occasion, with a standa rd zinc-free breakfast. In the postabsorptive state, fractional absorp tion was not affected by the quantity of zinc ingested until this exce eded 5 mg. When the zinc was administered with a meal, however, fracti onal absorption of 3 and 5 mg was less than for 1 mg. These results ar e compatible with the hypothesis that exogenous dietary zinc has to co mpete for absorption with endogenous zinc that has been secreted into the lumen of the gastrointestinal tract in response to a meal.