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United States Department of Agriculture

Agricultural Research Service

Breakfast Cereals Show Their Metal
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James H. Swain, PhD, RD

Did you know that most of the breakfast cereals lining the shelves of local supermarkets are fortified with iron? This dietary mineral is essential for growth, development, and performance of daily tasks.

Did you also know that the form of iron used to fortify many breakfast cereals resembles tiny "rocks"? These "rocks" are so small that hundreds could simultaneously fit through the eye of a needle. If you want to see these tiny rocks, crush any iron-fortified cereal and then try collecting them with a magnet.

Why is the iron in the form of tiny "rocks"? These particles are the result of the manufacturing processes used to produce iron powders. To begin, iron ore or scrap is taken through a series of reactions involving high temperatures and pressures. The product is then ground. When finished, the resulting iron powder particles resemble tiny rocks and, although differing in size, density, surface area, chemistry, and shape, are all greater than 98 percent iron.

But wait, there's more. Evidence suggests that the "physico-chemical differences" among various iron powders greatly influence their bioavailability or how well-absorbed they are by the body. Furthermore, the relative usefulness of iron powders produced by today’s manufacturing processes has not been fully explored and confirmed. For example, ferrous sulfate is a highly bioavailable iron source commonly used in iron supplements. But our preliminary research data with rats suggest that the bioavailabilities of some current, commercially produced iron powders range from 20 to 60 percent that of ferrous sulfate.

Research has shown that not all forms of iron are absorbed equally by the body. Although useful to improve nutrition, it is clear that the absorption of iron from cereals fortified with different iron powders varies. Different forms of iron also affect the foods they've been added to differently. The most easily absorbed forms of added iron can discolor foods or reduce their shelf-life. But elemental iron powders, which are more economical to produce and do not adversely affect the fortified food, are often used. Unfortunately, the traits that make iron powders less reactive with foods, may also decrease their bioavailability. One such trait is that the iron is in the form of tiny "rocks" or particles. The iron that makes up these particles is only available for absorption by the body once it dissolves from the particle. If the particle does not completely dissolve, its remnants pass through the gastrointestinal system.


Last Modified: 10/23/2006
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