The influence of previous iron intake on the estimation of bioavailability of Fe from a test meal given to rats.

Iron retention and its subsequent distribution from 3 g 59Fe extrinsically-labelled wholewheat four in rats given a low (8 micrograms Fe/g)- or high (566 micrograms Fe/g)-Fe diet during the previous 3 d was measured (Expt 1). The mean (with SE) proportion of Fe retained from wholewheat flour was 0.46 (0.04) in the group given the low-Fe diet and 0.15 (0.01) in the group given the high-Fe diet (P less than 0.001). There was no difference in distribution of absorbed 59Fe in the tissues examined. The procedure was repeated in rats given diets containing a range of Fe concentrations, groups 1-6 respectively: 8, 77, 136, 334, 566, 1270 micrograms Fe/g (Expt 2). The mean (with SE) proportions of Fe retained in groups 1-6 respectively were 0.60 (0.02), 0.34 (0.02), 0.30 (0.02), 0.20 (0.20), 0.17 (0.02), 0.09 (0.01). Regression analysis showed that Fe retention was a function of the logarithm of the Fe concentration of the diet consumed before the test meal (R -0.997, P less than 0.0001) where Fe retained (microgram) = 95 -28 log10 Fe concentration of diet. Rats were given a low-, medium- or high-Fe diet (8, 136 or 1270 micrograms Fe/g respectively) for 1 or 2 d instead of 3 d before measuring Fe retention from 3 g wholewheat flour (Expt 3). The mean (with SE) proportions of Fe retained in rats given the low-, medium- or high-Fe diets for 1 d were 0.45 (0.02), 0.25 (0.02) and 0.13 (0.01) (P less than 0.001) and for 2 d 0.47 (0.03), 0.31 (0.03) and 0.18 (0.02) (P less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)