Abstract
Protein is a main nutrient involved in overall iron metabolism in vivo. In order to assess the prevention of iron deficiency anemia (IDA) by diet, it is necessary to confirm the influence of dietary protein, which coexists with iron, on iron bioavailability. We investigated the usefulness of the egg structural protein in recovery from IDA. Thirty-one female Sprague-Dawley rats were divided into a control group (n = 6) fed a casein diet (4.0 mg Fe/100 g) for 42 days and an IDA model group (n = 25) created by feeding a low-iron casein diet (LI, 0.4 mg Fe/100 g) for 21 days and these IDA rats were fed normal iron diet with different proteins from eggs for another 21 days. The IDA rats were further divided into four subgroups depending on the proteins fed during the last 21 days, which were those with an egg white diet (LI-W, 4.0 mg Fe/100 g, n = 6), those with an ovalbumin diet (LI-A, 4.0 mg Fe/100 g, n = 7), those with an egg yolk-supplemented diet (LI-Y, 4.0 mg Fe/100 g, n = 6), and the rest with a casein diet (LI-C, 4.0 mg Fe/100 g, n = 6). In the LI-Y group, recovery of the hematocrit, hemoglobin, transferrin saturation level and the hepatic iron content were delayed compared to the other groups (p < 0.01, 0.01, 0.01, and 0.05, respectively), resulting in no recovery from IDA at the end of the experimental period. There were no significant differences in blood parameters in the LI-W and LI-A groups compared to the control group. The hepatic iron content of the LI-W and LI-A groups was higher than that of the LI-C group (p < 0.05). We found that egg white protein was useful for recovery from IDA and one of the efficacious components was ovalbumin, while egg yolk protein delayed recovery of IDA. This study demonstrates, therefore, that bioavailability of dietary iron varies depending on the source of dietary protein.
Highlights
Protein is one of the main nutrients involved in all aspects of in vivo iron metabolism including iron absorption, transport, hematopoiesis and storage [1,2]
This study demonstrates, that bioavailability of dietary iron varies depending on the source of dietary protein
Our results provided new finding that egg yolk protein delayed recovery of iron deficiency anemia (IDA) while ovalbumin was useful in recovery of IDA, and that the bioavailability of dietary iron varies depending on dietary protein source
Summary
Protein is one of the main nutrients involved in all aspects of in vivo iron metabolism including iron absorption, transport, hematopoiesis and storage [1,2]. By diet, it is necessary to confirm the influence and biological use of dietary protein, which coexists with iron, on iron absorption. Of the three major nutrients (carbohydrate, protein, and lipid), protein has been reported to have the greatest influence on iron absorption [3,4,5,6]. Cook et al reported that soybean protein inhibited iron absorption more than egg white protein by a factor of about 5 [7]. It has been reported that the absorptivity of iron from egg origin is low [12,13], iron absorption was shown to increase and contribute to a delay in the decrease in hemoglobin concentration in an iron-deficient state where iron demands were high [14].
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