title: Adaptation in human zinc absorption as influenced by dietary zinc and bioavailability.
abstract: BACKGROUND
  An understanding of the relations among dietary zinc intake, bioavailability, and absorption is necessary for making dietary intake recommendations.
  
  
  OBJECTIVE
  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.
  
  
  METHODS
  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 (65)Zn 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.
authors.affiliation: US Department of Agriculture-Agricultural Research Service Grand Forks Human Nutrition Research Center, Grand Forks, ND 58202-9034, USA. jhunt@gfhnrc.ars.usda.gov
authors.forename: Janet R
authors.initials: JR
authors.lastname: Hunt
authors.forename: Jeannemarie M
authors.initials: JM
authors.lastname: Beiseigel
authors.forename: LuAnn K
authors.initials: LK
authors.lastname: Johnson
mesh_terms: D000222:Adaptation, Physiological; D000328:Adult; D001682:Biological Availability; D015992:Body Mass Index; D018592:Cross-Over Studies; D004032:Diet; D004305:Dose-Response Relationship, Drug; D005260:Female; D006801:Humans; D007408:Intestinal Absorption; D008297:Male; D008875:Middle Aged; D009752:Nutritional Status; D010833:Phytic Acid / Q000494:pharmacology*; D015032:Zinc / Q000008:administration & dosage* / Q000493:pharmacokinetics*
chemical_list: D010833:Phytic Acid; D015032:Zinc