Recovery of dietary iron and zinc from the proximal intestine of healthy man: studies of different meals and supplements.
The technique of marker perfusion of the upper gastrointestinal tract was used to measure intraluminal quantities of iron and zinc after test meals in healthy humans. Two different meals, one based on hamburger (with a predominance of heme iron, 7.5 mg/meal) and one based on cereal (containing inorganic iron; 1.4, 5.3, or 4.6 mg), were used. In addition, the luminal behavior of ferrous sulfate and hydrogen-reduced metallic iron (used as supplements to the cereal meal) were compared. Different meals also contained low (2.4 mg) or high (5.5 mg) amounts of zinc. The intubation techique allowed disappearance of metals from the duodenum and jejunum to be compared. The patterns of luminal flow were different for iron and zinc. Whereas iron was never recovered from the lumen at levels above those ingested in meals, zinc was recovered from the duodenum at levels greater than those ingested. These findings suggest that zinc, but little iron, is added to chyme in the upper gut during digesting and absorption. Bioavailability of different forms of iron, as judged by their luminal disappearance, were similar. Inorganic iron, ferrous sulfate, and hydrogen-reduced metallic iron were absorbed about as effectively as was heme iron. Iron disappeared preferentially from the duodenum but the site of zinc absorption appeared to be more distal.