Factors affecting the absorption of iron from cereals

Abstract

1. Non-haem-iron absorption from a variety of cereal and fibre meals was measured in parous Indian women, using the erythrocyte utilization of radioactive Fe method.2. The present study was undertaken to establish whether alteration of the phytate and polyphenol contents of sorghum (Sorghum vulgare) affected Fe absorption from sorghum meals, and to assess the influence of fibre on Fe absorption.3. Removing the outer layers of sorghum grain by pearling reduced the polyphenol and phytate contents by 96 and 92% respectively. This treatment significantly increased the geometric mean Fe absorption from 0.017 to 0.035 (t 3.9, p < 0.005).4. The geometric mean Fe absorption from a sorghum cultivar that lacked polyphenols (albino sorghum) was 0.043, which was significantly greater than the 0.019 absorbed from bird-proof sorghum, a cultivar with a high polyphenol content (t 2.83, p < 0.05).5. Fe was less well absorbed from the phytate-rich pearlings of the albino sorghum than from the pearled albino sorghum (0.015 v. 0.035 (t 8.4, P < 0.0005)). Addition of sodium phytate to a highly Fe-bioavailable broccoli (Brassica oleracea) meal reduced Fe absorption from 0.185 to 0.037.6. The geometric mean Fe absorption from malted sorghum porridge was 0.024 when 9.5 mg ascorbic acid were added and 0.094 when the ascorbic acid was increased to 50 mg (t 3.33, P < 0.005). This enhancing effect of 50 mg ascorbic acid was significantly depressed to 0.04 by tea (t 38.1, P < 0.0005).7. Wheat bran significantly decreased the geometric mean Fe absorption from white flour from 0.116 to 0.043 (t 7.2, P < 0.0005).8. Some of the constituents of the dietary fibre complex, such as apple pectin, guar gum, gum tragacanth and microcrystalline cellulose did not inhibit Fe absorption. On the other hand, hemicellulose and lignin decreased absorption. The geometric mean absorption of Fe given with hemicellulose was 0.079 v. 0.269 with microcrystalline cellulose (t 2.95, P < 0.05). Addition of cocoa, which contains approximately 280 g lignin/kg, reduced the geometric mean Fe absorption from milk from 0.075 to 0.035 (t 2.7, P < 0.05).