THE BIOAVAILABILITY OF IRON IN DIFFERENT WEANING FOODS AND THE ENHANCING EFFECT OF A FRUIT DRINK CONTAINING ASCORBIC-ACID

There is limited information on the bioavailability of Fe in infant we aning foods, mainly because of the difficulties of measuring Fe utiliz ation directly in infants. The aim of this study was to develop a safe and relatively noninvasive method for studying Fe bioavailability (me asured as percent Fe incorporation into red blood cells) in infants us ing Fe-54, Fe-57, and Fe-58 stable isotopes. Four commonly used weanin g foods were selected for study, labeled extrinsically with Fe-57- or Fe-58-enriched ferrous sulfate, and fed to five female and five male 9 -mo-old fasting infants, using a multiple-dosing technique. Each food was given three times, labeled with one isotope, with a fruit juice dr ink containing 50 mg of ascorbic acid, and three times, labeled with a different isotope, with an ascorbic acid-free drink. Fourteen days af ter the last test meal, a blood sample was obtained from a heel-prick, spiked with a known amount of Fe-54, digested, and purified by ion ex change; isotopic enrichment and total Fe content were measured by quad rupole thermal ionization mass spectrometry. The proportion of adminis tered dose of isotope circulating in the blood was calculated from an estimate of blood volume. The geometric mean bioavailability (range) w as 3.0% (1.2-9.5%) in a proprietary dehydrated vegetable product, 3.0% (1.1-21.2%) in Weetabix whole-wheat breakfast cereal, 3.1% (1.2-15.4% ) in wholemeal bread, and 4.3% (1.7-10.3%) in baked beans. When taken with the drink containing ascorbic acid, there was a 2-fold increase i n bioavailability in all foods except the vegetable meal, presumably b ecause this was already fortified with ascorbic acid. Thus, drinks con taining 50 mg of ascorbic acid, taken with a meal, can significantly i mprove Fe bioavailability to infants from weaning foods low in ascorbi c acid.