Iron absorption and intestinal solubility in rats are influenced by dietary proteins

Abstract

The effects of different proteins (pork, egg albumin, egg yolk, soybean and casein) on iron absorption and intestinal solubility were examined in growing rats. Rats were fed iron-adequate diets including one of the protein sources for 14 d. All the diets were adjusted to contain similar levels of protein (220 g crude protein /kg diet) and iron (51–53 mg iron /kg diet). Apparent iron absorption was determined using conventional chemical balances. Soluble iron in the intestinal contents and plasma iron concentration in portal blood were determined shortly after the meal. Portal blood iron and intestinal soluble iron were highly correlated (r = 0.92, p = 0.042). The addition of pork protein greatly improved the solubility (42%) and apparent absorption (42%) of iron. In contrast, in rats fed egg yolk protein, iron solubility (17%) in the small intestine significantly decreased together with apparent iron absorption (13%) and iron concentration of the portal blood when compared with other groups. The effects of proteins on intestinal solubility and apparent absorption of iron were in increasing order: egg yolk < soybean < egg albumin < casein < pork. Our results suggest that the iron enhancing/inhibiting effect of pork/egg yolk results from their protein fractions. The iron solubility in the small intestine may be responsible for the difference in iron absorption of various proteins.