Iron is needed for
numerous body
functions

But because iron is essential for many functions in the body, a deficiency can result in a wide variety of symptoms. Even without anemia, iron deficiency can cause fatigue, exhaustion, restless legs syndrome, attention deficit disorder and a decreased ability to concentrate -- among other problems.

People diagnosed with iron deficiency are typically given a list of foods that contain iron and are encouraged to eat more of them. Such lists are widely available in nutrition textbooks and on university or hospital Web sites. Too often, however, these lists mindlessly include foods that contain significant amounts of iron but are actually very poor "sources" of iron.

Q: What makes a food a good source of iron?

A: Most of the iron in foods merely passes through the intestinal tract and is not absorbed. For a food to be a good source of iron, the iron must be in a chemical form readily absorbed into the body. These sources are called bioavailable -- the iron is biologically available to the body.

Animal flesh foods have the highest iron bioavailability, with darker meats and poultry cuts containing greater amounts than lighter flesh. Most plant foods containing iron have other components that inhibit absorption of iron. Foods such as beans, nuts and high-fiber vegetables and grains generally provide little absorbable iron and can inhibit overall iron absorption.

Spinach often is listed as high in iron, but because almost all the iron is in a form that cannot be absorbed, it is actually a poor source. The amazing powers that Popeye obtained from spinach were due to something besides iron -- perhaps a placebo effect.

Information about iron bioavailability is limited, and much remains to be learned. To help fill this knowledge gap, a research project is beginning at the University of Hawaii. Led by Dr. Michael Dunn at the University of Hawaii Department of Human Nutrition, Food and Animal Sciences, the study will evaluate the iron bioavailability of many local foods.