Adaptation in human zinc absorption as influenced by dietary zinc and bioavailability
2008
Hunt, Janet R. | Beiseigel, Jeannemarie M. | Johnson, LuAnn K.
BACKGROUND: An understanding of the relations among dietary zinc intake, bioavailability, and absorption is necessary for making dietary intake recommendations. OBJECTIVES: We aimed to assess adaptation in human zinc absorption to controlled differences in zinc and phytate intakes and to apply the results to predictive models. DESIGN: In 3 experiments, radiotracers were used to assess zinc absorption by healthy adults (n = 109) from controlled diets, before and after 4 or 8 wk of dietary equilibration. Subjects consumed 4-29 mg Zn/d from 1 of 10 diets, 5 with molar ratios of phytate to zinc from 2 to 7 and 5 with ratios from 15 to 23. RESULTS: Absorptive efficiency was inversely related to dietary zinc from both low- and high-phytate diets. In response to low zinc intakes (<11 mg/d) for 4-8 wk, zinc absorption was up-regulated to as high as 92%, but only if the diets were low in phytate. The results help validate and refine a published saturable transport model that predicts zinc absorption from dietary zinc and phytate. Possible biomarkers of impaired zinc status, including erythrocyte osmotic fragility, in vitro erythrocyte ⁶⁵Zn uptake, and leukocyte expression of the zinc transport proteins Zip1 and ZnT1, were unresponsive to dietary zinc content. CONCLUSIONS: Humans absorbed zinc more efficiently from low-zinc diets and adapted to further increase zinc absorption after consuming low-zinc, low-phytate diets for several weeks. Such adaptation did not occur with higher phytate diets. Zinc absorption can be predicted from dietary zinc and phytate after allowing for dietary equilibration.
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