Iron absorption from infant foods.
To determine the bioavailability of iron from iron-fortified infant foods, we have determined erythrocyte incorporation of the stable isotope, 58Fe, after feeding the following foods extrinsically labeled with 58Fe: 1) rice cereal with apples and bananas ("cereal-fruit product"), 2) Mead Johnson Enriched Baby Food (MJEBF), a vitamin, mineral, and protein-enriched rice cereal, 3) vegetables and beef ("vegetable-beef product"), 4) grape-juice, and 5) MJEBF. Foods 1-4 were fortified with ferrous sulfate, and food 5 was fortified with ferrous fumarate. Blood was obtained at ages 140, 168, and 196 d of age, and the test meal was fed under standardized conditions at 154 d of age. Erythrocyte incorporation of the 58Fe label was determined from the increase in the mass isotope ratio, 58Fe/57Fe, from the baseline value (at 140 d of age) to the follow-up values. The mass isotope ratio was determined by inductively coupled mass spectrometry. Geometric mean total iron incorporation into erythrocytes from the test meal of MJEBF fortified with ferrous sulfate (food 2) was 0.05 mg, and from the vegetable-beef product test meal (food 3) was 0.08 mg. The low value for MJEBF is presumably explained by the low level of iron fortification. The low value for the vegetable-beef product may reflect the presence of inhibitors of iron absorption. Geometric mean erythrocyte incorporations of iron from the test meals with foods 1, 4 and 5 were 0.15, 0.14, and 0.18 mg, respectively. These erythrocyte incorporation values are 20 to 26% of the estimated 0.7 mg requirement for absorbed iron, and therefore seem nutritionally important.