Homeostatic Adjustments in Zinc Digestion to Widely Varying Dietary Zinc Intake

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Abstract
A 15-day Zn balance study was conducted with 36 growing rats maintained on a casein diet with 18.2 µg Zn/g from day 0 to 3. Thereafter, six rats each were given the diet with the following variates of Zn content (µg Zn/g): 5.6, 10.6, 18.2, 39, 70, 141. Zn digestion adjusted to the change in dietary Zn intake within the first 6 days via control of the extent of intestinal Zn absorption and fecal excretion of endogenous Zn. From day 9 to 15, mean apparent Zn digestion ranged from 92 to 18% and Zn absorption from 100 to 34% in an inverse relation to Zn intake. At the supply of 39 and 70 µg Zn/g of diet, fecal excretion of endogenous Zn amounted to nearly one fourth of the dietary Zn intake. Reduction of intestinal absorption became the major factor to confine Zn accretion by the body when Zn intake was in great excess above requirement. Endogenous fecal Zn excretion exhibited its greatest homeostatic response in the range of optimum Zn intake. Zn excretion via the kidneys did not partake in Zn homeostasis, except that it was a major drain of body Zn compared to the intestinal route at low Zn intakes.