Objective: To validate a new method of measuring iron absorption from the whole diet over several days, to compare iron absorption from two types of diets and to relate iron absorption to iron requirements and iron stores.
Design: Iron absorption from two diets was studied in 21 healthy young women. All non-haem iron in all meals was labelled to the same specific activity with an extrinsic radio-labelled iron tracer. Haem iron absorption was calculated from the amount of haem iron and absorption from a reference dose of iron.
Results: Iron absorption was concordant with individual iron requirements measured from menstrual blood losses and body weights. Total iron absorption from one diet designed to be highly bioavailable, would cover iron requirements in about 94% of menstruating women. Iron absorption was reduced by half from a diet with less meat, more phytate and more calcium with main meals. This type of diet would cover iron requirements in only 65% of adult menstruating women. For both diets there was a marked reduction in iron absorption with increasing serum ferritin. Iron balance was not positive above a serum ferritin of about 60 micrograms/l.
Conclusions: Bioavailability of dietary iron is a key factor in iron nutrition. A diet with much lean meat, ascorbic acid and a low phytate content can cover iron requirements in most non-pregnant women. The powerful control of iron absorption implies that dietary iron overload cannot develop in normal subjects, even with diets having high iron content or high bioavailability.