The RDA values are based on the assumption that the consumer eats a mixture of plant and animal foods. The above list of iron values alone may be deceptive, since the availability of iron in fruits, vegetables, and grains is very low, while that the availability from meat is much higher. The term availability means the percent of dietary iron that is absorbed via the gastrointestinal tract to the bloodstream. Non-absorbed iron is lost in the feces. Interactions between various foods can influence the absorption of dietary iron.
Vitamin C can increase the absorption of dietary iron.
Thus, if a plant food, such as rice, is consumed with orange juice, then the orange juice can enhance the absorption of the iron of the rice. Phytic acid is a chemical that naturally occurs in legumes, cereals, and nuts. Nearly all of the iron in plants is nonheme-iron. Much of the iron in meat is nonheme-iron as well. When an abnormally high presence of blood is found in the feces during a fecal occult blood test, the physician needs to examine the gastrointestinal tract to determine the cause of bleeding.