Components found in wheat bran and spinach were evaluated as to their affect on the bioavailability of ferrous iron (i.e., FeSO4) by using the criteria of hemoglobin regeneration in anemic rats. The relative biological value (RBV) of iron in wheat bran and spinach (FeSO4 = 100%) were determined to be 124 and 53%, respectively. Control diets with graded levels of FeSO4 did not contain dietary fiber (i.e., cellulose). Adding cellulose (1.74%) or phytic acid (0.66%) at levels contained in the wheat bran diet, significantly increased (P less than 0.05) the RBV f the ferrous iron to 126 and 124%, respectively. The addition of 2.10% oxalic acid, the amount in the spinach diet, caused the highest increase in RBV to 164%. Combining these dietary components, plus lignin (0.67%) and pectin (0.63%), in various combinations, resulted in RBVs equivalent or significantly higher than 100%. The bioavailability of iron in plant foods appears to be dependent on how this nutrient is presented to the mucosa. Cellulose, phytate or oxalate added to a purified diet containing ferrous iron significantly enhanced the bioavailability of this element. Relative biological values for iron were also calculated based on food intake and growth rate. The latter parameters are believed to have greater utility in determining RBV when food intake and/or growth rate may vary among animals consuming different sources of test iron.
The effect of fish protein and fish oil on the utilization of endogenous iron in wheat bran, spinach and soy protein isolate was investigated by using the anemic rat as an animal model. Marine products were substituted for casein and corn oil in the diets of these animals. Hemoglobin regeneration was one criteria used to measure iron uptake. Relative biological values (RBV) were computed from a regression equation obtained from control animals receiving graded levels of FeSO4 X 7H2O. The RBV of iron from plant sources provided in diets containing casein-corn oil versus fish-fish oil were: wheat bran, 123 vs. 111%; spinach, 53 vs. 49%; and soybean isolate, 84 vs. 67%; RBV FeSO4 = 100%. These changes were not significant. The decreases in iron absorption from diets containing marine products was attributed to the fish oil. Absorption of exogenous iron (59Fe) was measured in the same animals after the 14-day repletion period. Assimilation of the 59Fe was highly correlated (r2 = 0.958) with hemoglobin level at time of dosing. Diet composition did not appear to have the same effect on the percentage of 59Fe retained after 110 hours by the rat as compared to levels of hemoglobin regeneration (i.e., RBV). A "meat factor" effect was not shown by substituting fish for casein the diets containing plant iron sources fed anemic rats.
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