Many cereals and other foods contain iron which is needed by the body and is absorbed by the small intestine. Iron is found mainly in a very important component of blood called hemoglobin. Hemoglobin is the compound in red blood cells that carries oxygen from the lungs, so it can be used by our body. A diet poor in iron can lead to fatigue, reduced resistance to disease, as well as increased heart and respiratory rate. Scientists say that a healthy adult needs about 18 mg of iron each day.