Nutritional significance of interactions between iron and food components

Most food iron in the gut enters into two "common pools" that behave quite differently in terms of absorption. Heme iron present in hemoglobin and myoglobin, is well absorbed and is relatively unaffected by diet composition. Non-heme iron, the form of iron present in vegetables and in man's staples, generally is poorly absorbed and is greatly affected by enhancing or inhibiting substances in the diet. In experiments employing intrinsically-labeled hemoglobin as a tracer, absorption of a dry hemoglobin concentrate added to milk, a rice cereal and wheat cookies, was uniformly good, relatively constant and quite independent from the type of food. In contrast, absorption of iron salts decreases markedly when given with food. The presence or absence of inhibiting or enhancing factors of non-heme iron absorption is determinant in the possibility of obtaining required iron for most people in the world whose diet contains little heme iron. Meat and ascorbic acid are the main enhancers of non-heme food iron absorption. Common inhibitors include carbonates, oxalates, phytate, bran, tea and egg yolk. The enhancing effect of ascorbic acid on the absorption of fortification iron in milk and the effect of tea, eggs or meat on the absorption of bread iron from common Chilean meals are discussed as examples of interactions of food components with non-heme iron.