Non-heme iron is absorbed in the duodenum. This part of the small intestine is the most acidic and therefore favorable to the solubility of the iron.
While the absorption of heme iron is almost constant, the one of non-heme iron varies largely and can be multiplied by 10 to 15 depending on:
Adaptations of the body according to the reserves
The body can adapt itself to an excess as well as to a lack of iron. When the iron has been absorbed, the body does not have the possibility to excrete it (or just in small quantities). Thus, the absorption must be regulated to avoid an iron excess in the body.
In normal conditions, the body absorbs and excretes 1 mg of iron a day.
When iron is in excess, the absorption can be reduced to 0.5 mg and the excretion increased until 1.5 mg.
Vegetarians are concerned about the adaptations when they are deficient. In this case, excretion can be as low as 0.5 mg and the absorption can reach 5 mg per day.
The inhibitors of the absorption
The solubility of the iron in the bowel determines its absorption.
Phytates and phenolic compounds which are largely found in the vegetable world are known to bind with the non-heme iron and make it insoluble. It is out of question to eliminate these foods from our diet since they provide also large amount of proteins, dietary fiber, vitamins and minerals. However, we can reduce the phytates content of legumes and cereal by soaking them before cooking. Once roasted, nuts and cereal have lost most of their phytates.
Because tea contains tannins, vegetarians should be careful and not drink too much of this beverage. The action of tannins is dose dependent, which means that the more they are present in the meal, the more the absorption of the iron is decreased.
It is thus preferable to consume tea and coffee, which contains these compounds too, between meals and in small quantities.
Other inhibitors are; calcium, zinc and certain proteins.
Remarks: fibers do not limit the absorption of iron. It is because the foods which are rich in fiber are very often as well rich in phytates. That is why we often make the confusion.
The friends of iron
Vitamin C is THE vitamin as regards to the absorption of iron. However, it is interesting only if it is taken during the meal. A unique dose of vitamin C a day does not increase iron absorption during the day but only at the meal which follows the ingestion. It is thus better to consume a little vitamin C at every meal. Vegetables contain some vitamin C but fruits and mainly citrus fruits are very rich. Vegetarians have to make sure they have a good source of vitamin C at every meal.
Realized by Laurence LIVERNAIS-SAETTEL, dietitian
© Copyright L. Livernais-Saettel 2003
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