Food iron absorption measured by an extrinsic tag

The effect of tea on iron absorption

The effect of tea on iron absorption was studied in human volunteers. Absorption from solutions of FeCl3 and FeSO4, bread, a meal of rice with potato and onion soup, and uncooked haemoglobin was inhibited whether ascorbic acid was present or not. No inhibition was noted if the haemoglobin was cooked. The effect on the absorption of non-haem iron was ascribed to the formation of insoluble iron tannate complexes. Drinking tannin-containing beverages such as tea with meals may contribute to the pathogenesis of iron deficiency if the diet consists largely of vegetable foodstuffs.

Iron absorption from rice meals cooked with fortified salt containing ferrous sulphate and ascorbic acid

1. Iron absorption from rice-containing meals was measured by red cell utilization of radioactive Fe in sixty-six volunteer multiparous Indian women.

2. In all the studies salt added during the cooking process was used as the carrier for supplemental inorganic Fe and ascorbic acid.

3. Intrinsic Fe in the rice and supplementary inorganic Fe were absorbed to the same extent, with a wide range of absorption values.

4. There was a striking difference between the mean absorption of a 3 mg dose of ferrous Fe given to fasting subjects in a solution containing 30 mg ascorbic acid and that of Fe in a rice meal (48.7 and 3.5% respectively).

5. When ascorbic acid was added during cooking there was a threefold increase in the absorption of both intrinsic Fe and supplementary Fe when a sufficient quantity (60 mg) was present.

6. It is concluded that the Fe nutrition of rice-eating communities could be improved significantly by the addition of ascorbic acid to the diet.

Food iron absorption in man. Applications of the two-pool extrinsic tag method to measure heme and nonheme iron absorption from the whole diet

A new radioisotope method to measure iron absorption from the whole diet was used in this study. The method is based on the concept that food iron is absorbed from two pools, the heme iron pool and the nonheme iron pool, which can be especially labeled with two radioiron isotopes given as hemoglobin and as an iron salt. The purpose of this study was to test the accuracy of this two-pool extrinsic tag method. The meals served were composed as an average of 6 wk consumption in the present material of 32 young enlisted men. The mean and total heme and nonheme iron absorption in all the 32 young men was 1.01+/-0.11. This figure agrees well with the mean daily losses expected for this group of subjects (1.0 mg). The conclusion can therefore be made that there are no major systematic errors of the present method to measure the total iron absorption from a mixed diet. In one series a comparison was made of the absorption of heme and nonheme iron from the meals. A significant correlation between the absorption of the two kinds of iron was found. However, a much greater fraction of the heme iron was absorbed (37%) than of the nonheme iron (5%). The absorption both from breakfast and lunch was in two series found to give a good prediction of the total daily nonheme iron absorption. One series was designed to compare the effect of two levels of iron fortification. There was a significant increase in iron absorption when the level of iron fortification of the meals was increased.

The effects of ascorbic acid supplementation on the absorption of iron in maize, wheat and soya

The absorption of iron from three staple vegetables was measured by the red cell utilization method in iron deficient subjects. The food iron had been labelled with 55Fe by the hydroponic cultivation method. In addition, 59Fe was added with or without carrier iron in the form of ferric ammonium citrate, prior to cooking. The constant relationship reported by others between the absorption of the two isotopes was confirmed, suggesting that the extrinsic iron and the food iron were absorbed from a common pool. The addition of ascorbic acid to maize porridge before cooking significantly enhanced the absorption of both the intrinsic and the added iron. However, no effect was noted with soya biscuits or with whole wheat bread (100% extraction). Evidence was obtained that these differences were due to the oxidative destruction of the ascorbic acid by the high temperatures required for baking. If, therefore, a feasible method were found for supplementing vegetable foodstuffs with ascorbic acid and inorganic iron, nutritional benefit would only be anticipated with uncooked or boiled foods.