Adaptation of iron absorption in men consuming diets with high or low iron bioavailability

Abstract

Background: Short-term measurements of iron absorption are substantially influenced by dietary bioavailability of iron, yet bioavailability negligibly affects serum ferritin in longer, controlled trials. Objective: Our objective was to test the hypothesis that in men fed diets with high or low iron bioavailability, iron absorption adapts to homeostatically maintain body iron stores. Design: Heme- and nonheme-iron absorption from whole diets were measured in 31 healthy men at 0 and 10 wk while the men consumed weighed, 2-d repeating diets with either high or low iron bioavailability for 12 wk. The diets with high and low iron bioavailability contained, respectively, 14.4 and 15.3 mg nonheme Fe/d and 1.8 and 0.1 mg heme Fe/d and had different contents of meat, ascorbic acid, whole grains, legumes, and tea. Results: Adaptation occurred with nonheme- but not with heme-iron absorption. Total iron absorption decreased from 0.96 to 0.69 mg/d (P < 0.05) and increased from 0.12 to 0.17 mg/d (P <0.05) after 10 wk of the high- and low- bioavailability diets, respectively. This partial adaptation reduced the difference in iron bioavailability between the diets from 8- to 4-fold. Serum ferritin was insensitive to diet but fecal ferritin was substantially lower with the low- than the high-bioavailability diet. Erythrocyte incorporation of absorbed iron was inversely associated with serum ferritin. Conclusions: Iron-replete men partially adapted to dietary iron bioavailability and iron absorption from a high-bioavailability diet was reduced to ≃0.7 mg Fe/d. Short-term measurements of absorption overestimate differences in iron bioavailability between diets.