Review:: Effect of some components of milk- and soy-based infant formulas on mineral bioavailability

Infants' high nutritional needs are fulfilled by mother's milk or infant formulas to provide all the necessary nutrients, among them minerals. Minerals uptake depends not only on mineral content but also an their bioavailability which, in turn. is affected by the different components of the infant formulas. An understanding of these effects would help to improve mineral bioavailability. This work reviews the influence of endogenous (proteins and phytates) and added (ascorbic and citric acid) components in infant formulas on the bioavailability of nutritionally important mineral elements (calcium, zinc, iron and copper) and their interactions. Special attention is given to the influence of protein, which is positive for calcium and negative for iron absorption. The marked negative effect of phytates on iron and zinc absorption can be counteracted by a dephytinization process. Of the added compounds, ascorbic acid has a positive effect on iron absorption that depends on the molar ratio between ascorbic acid and iron. In fact, adding ascorbic acid can counteract the negative effect of phytic acid on iron absorption but does not alter the effect of phytic acid on zinc absorption. The null effect of an increase in citric acid content can be ascribed to the fact that the citrate contents of infant formulas are already high. One of the most important element interactions is the negative effect of calcium on zinc and iron intestinal absorption and also the interaction between zinc and iron. These interactions deserve our attention because these minerals are essential to infants' growth and development.