Iron is an important trace minerals required for for formation of haemoglobin and as a cofactor in a number of enzymes such as tyrosine hydroxylase. The absorption of iron is complicated by the fact that two dietary sources are available. Haem iron is found in the flesh of animal tissues and is well absorbed in humans. Haem iron mainly comprises of the haemoglobin and myoglobin in the blood and muscle tissue of animals, respectively. Non-haem-iron is found in tissues of plant origin and has much lower absorption rates than haem iron. The iron absorption of vegetarians may therefore be inferior to omnivorous humans due to the types of iron that make up the diet. Interestingly, the absorption of nonheme iron can be enhanced by addition of meat to the meal. For example adding 100 grams of fish to a meal containing non-haem iron increases the absorption of the non-haem iron to the same level as the iron in the fish. Meat tissue may therefore have factors that increase the absorption of iron.
The ability of animal proteins to alter the absorption of iron has been tested in comparison to proteins of non-animal origin1. Under simulated gastrointestinal conditions using pepsin and pancreatin digestion, the amount of iron which passed into a dialysis sac was measured as an estimate of iron absorption. This method had been developed and tested previously by Miller2. The results showed that iron absorption was highest for beef protein and serum bovine albumin, intermediate for egg and egg albumin, and lowest for soy flour, gelatin, casein, soy protein isolate and gluten. When the authors analysed the results they found that low molecular weight protein digestion fractions from bovine serum albumin and beef protein enhanced the absorption of iron. Therefore one way that animal tissue may enhance the absorption of iron is through the formation of low molecular weight protein iron complexes that are more likely to cross the brush border of the enterocytes, increasing the bioavailability of the iron.
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