Zinc and calcium apparent absorption from an infant cereal: A stable isotope study in healthy infants

Fractional apparent absorption of Zn and Ca from a wheat-milli-based infant cereal was studied in six healthy infants (18-30 weeks old), Mineral absorption was measured by a stable-isotope technique based on faecal excretion of the isotopes, Each test meal (40 g cereal) was extrinsically labelled with Zn-70 and Ca-42 before intake, All faecal material passed during the 21 d following intake of the labelled test meal was collected on trace-element-free nappies, Individual stool samples were analysed for their content of Zn-70 and Ca-42 by thermal ionization mass spectrometry, Apparent absorption was calculated as intake minus total faecal excretion of the isotopes over 68-92 h after administration. The fractional apparent absorption values for Zn and Ca were 33.9 (SD 16.4)% (range 19.2-63.9 %) and 53.5 (SD 12.6) % (range 36.7-71.7 %) respectively. Re-excretion of absorbed Zn-70 (> 68-92 h to 21 d after intake of the labelled meal) was 0.44 (SD 0.38)% of administered dose while only one infant re-excreted detectable amounts of Ca-42 (1.74 % of administered dose), The analysis of individual stool samples confirmed that 72 h is a sufficient time period for complete collections of non-absorbed isotopes in faecal material from infants during the weaning period and that re-excretion of initially absorbed Zn-70 and Ca-42 (> 68-92 h to 21 d after intake of the labelled meal) is negligible.