Author
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Hunt, Janet |
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Submitted to: The American Journal of Clinical Nutrition
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 6/17/2003 Publication Date: 9/1/2003 Citation: Hunt, J.R. 2003. High-, but not low-bioavailability diets enable substantial control of women's iron absorption in relation to body iron stores, with minimal adaptation within several weeks. American Journal of Clinical Nutrition. 78:1168-77. Interpretive Summary: Dietary iron bioavailability, or the amount of iron absorbed from diets, can vary substantially depending on the food sources of iron, such as the well-absorbed heme iron from meat, and of additional food components, that enhance or inhibit iron absorption. Over time, men partially adapt to these dietary differences. Premenopausal women, with their lower iron stores, may be less likely than men to adapt their iron absorption in response to dietary iron bioavailability. We tested heme and nonheme iron absorption from whole diets consumed by 36 healthy premenopausal women for 12 wk. The high and low bioavailability diets contained similar total iron, but differed in the content of meat, ascorbate, whole grains, legumes, and tea. The women absorbed 6 times more iron from the high, compared with the low bioavailability diet, and there was only a slight tendency to adapt to this difference in iron bioavailability. Only the high bioavailability diet enabled women with the lowest iron stores to substantially increase their iron absorption. Technical Abstract: Premenopausal women, with their lower iron stores, may be less likely than men to adapt their iron absorption in response to dietary iron bioavailability. We tested whether women adapt their iron absorption, modifying the influence of dietary iron bioavailability, and if adaptation reflects altered absorptive efficiency or adjustment to specific inhibitors or enhancers of absorption. Heme and nonheme iron absorption from whole diets by 36 healthy premenopausal women were measured in a 12 wk controlled diet study, using a randomized 2X2 factorial design with 2 levels of dietary iron bioavailability and both long-term (12 wk) and short-term (2 d of radiolabeled meals at 0 and 10 wk) dietary treatments. The high and low bioavailability diets contained similar total iron, as 13.1 and 14.8 mg/d nonheme and 2.0 and 0.3 mg/d heme iron, respectively, and differed in content of meat, ascorbate, whole grains, legumes, and tea. Premenopausal women tended to adapt their efficiency of nonheme (p<0.055, 2-tailed test), but not heme iron absorption in response to a 12-wk difference in dietary iron bioavailability, whether absorption was tested with high or low bioavailability menus. Bioavailability, but not adaptation, substantially influenced total iron absorption (~6-fold). Only the high bioavailability diet enabled an inverse association between iron absorption and serum ferritin (R2 of 0.79 vs. 0.08 with low bioavailability). In conclusion, only the high bioavailability diet enabled women with low iron stores to substantially up-regulate their iron absorption, absorbing as much as 4.5 mg, or 30-35% of dietary iron without substantial adaptation. |
