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Relative availability of iron to rats from beef, soy protein and a beef-soy protein mixture as determined by iron repletion assay Nikolaiczuk, Marcia Jane


Male weanling Wistar rats were fed a low-iron basal diet for 3 weeks. The iron depleted rats were then divided into 9 groups according to a randomized block design based on body weight. During the repletion period of 2 weeks, one group was fed the low-iron basal diet. The other eight groups received either the basal diet to which was added 5, 10, 15, 20 or 25 mg iron per kg diet as ferrous sulfate or test source diets formulated to provide a total of 15 mg iron per kg diet from either freeze-dried ground beef, textured defatted soy flour product or a 2.3:1 (w/w) mixture of beef and soy product. All diets were isocaloric and isonitrogenous. The relative biological value (RBV) of iron in the test source diet was calculated as the ratio of the amounts of iron from the reference source (ferrous sulfate) and the test source diet required to give the same response in hemoglobin or hematocrit. The RBVs ± 95% confidence limits, calculated on the basis of final hemoglobin levels and hematocrit values, were respectively: freeze-dried ground beef, 56 ± 7 % and 62 ± 7 %; fortified textured defatted soy flour product, 81 ± 10 % and 79 ± 10 %; 2.3:1 (w/w) mixture of freeze-dried ground beef and soy flour product, 65 ± 6 % and 68 ± 6 %. The RBVs obtained for the iron in beef and for that in the soy flour product suggest that the anemic rat might not be a suitable model for normal man when screening such foods for their available iron. In normal man, the absorption of the iron in beef is comparable to that of inorganic reference iron, while that in textured soy flour is about one third.

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