Effects of some carbohydrates on iron absorption

Two experiments were performed to examine the effects of various carbohydrates (fructose, lactose, corn starch, wheat starch and potato starch) on the utilization of iron, on Fe-depleted rats. These received a single meal that contained the test carbohydrate at a 60% level, labelled with 59Fe. The rest of the experiment the rats were fed a diet which contained glucose at a 60% level as the carbohydrate source. In both experiments rats were fasted overnight, and the dose was offered in the form of a morning meal. To assay for 59Fe, the animals were counted in a "Whole body counter" between two and four hours after dosing, and every day for the following 10 days. Percentage retention and absorption, as well as hemoglobin values were determined. In the first experiment, the replacement of glucose by fructose at a 60% level enhanced significantly iron absorption and retention. An increase in absorption and retention also occurred when glucose was replaced by lactose at a 60% level, but the difference was not statistically significant. Administration of 59Fe as an 59Fe-fructose chelate did not seem to have a significant effect on retention and absorption when compared to the effect of dosing with 59Fe adsorbed onto a fructose diet. This not rule out the possibility that chelation is the mechanism responsible for the enhancing effect of fructose on iron utilization. The complex could have been formed in the stomach, resulting in a significant absorption for both the 59Fe-labelled meal and the 59Fe-carbohydrate complex-labelled meal. In the second experiment, administration of a meal that contained either of the starches resulted in a reduction on retention and absorption of 59Fe. The decrease, however, was statistically significant only for cooked corn starch, wheat starch and cooked wheat starch. The effect of cooking was to reduce even more the retention and absorption of 59Fe, but this reduction was statistically significant only for corn starch. The depressing effects of starches on iron retention and absorption are quite relevant to human nutrition. In the developing countries, diets are generally high in cereal products - often whole grain cereals - and low in animal products. The inhibitory effects of cereals on iron absorption have been traditionally attributed to the presence of phytates and fiber, but the data herein presented suggest that high intakes of starches may be inhibitory as well.