Final answer:
The bioavailability of iron is highest in meat, poultry, and fish, which provide heme iron that is more efficiently absorbed compared to non-heme iron in plant-based foods. Absorption is affected by the gastrointestinal pH and is enhanced by protein.
Step-by-step explanation:
The student is inquiring about the bioavailability of iron in different food groups. Generally, there are two types of iron found in our diet: heme iron and non-heme iron. Heme iron, which comes from animal sources such as meat, poultry, and fish, is absorbed more efficiently by the body. Non-heme iron from plant sources tends to be absorbed at a lower rate. The intake of iron is also enhanced when accompanied by certain substances such as proteins, which might increase absorption through the formation of soluble iron chelates.
Iron absorption mainly occurs in the duodenum and proximal jejunum. The acidic pH of the gastrointestinal tract, like the pH found in the stomach at pH 1.0, dissolves most Fe(III) salts, making the iron available for absorption. Furthermore, foods and drinks are often fortified with iron, either as Fe2+ salts or reduced iron, to ensure adequate iron intake. For example, bread and breakfast cereals might contain reduced iron, which is iron in the form of a fine metallic powder that gets oxidized to Fe2+ before being absorbed in the digestive system.