Iron speciation in intestinal contents of rats fed meals composed of meat and nonmeat sources of protein and fat

Our objective was to test the hypothesis that interactions of iron with protein and fat digestion products are responsible for the iron-absorption-enhancing properties of meat. Rats were fed meals labeled with 59 FeCl 3 and 14 C-oleic acid, formulated from various combinations of protein and fat sources (lean beef, skim milk or egg white; tallow, butter or vegetable shortening). After 30 min, iron absorption was determined, and stomach and intestinal contents were collected and fractionated by gel filtration chromatography. Iron absorption was highest from the beef + tallow and beef + shortening meals. Different protein sources produced different Chromatographic profiles of peptides in the intestinal lumen. Soluble iron in intestinal contents was associated with peptides, but not with amino acids, fatty acids or bile salt micelles. Results suggest that specific peptides produced during protein digestion may be one factor influencing iron bioavailability.