The binding of iron to different fibers suggest in vitro that dietary fibers might interfere with the bioavailability of iron in the diet. As it is difficult or impossible to translate in vitro studies to in vivo bioavailability and even to translate results from animal studies to man, it is necessary to study the effect of fiber in man. With the extrinsic tag method and two different radioiron tracers it is possible in the same subject to compare the iron absorption from a meal with and without a certain component of dietary fiber. With a standard reference dose of 3 mg iron it is possible to "calibrate" each subject which makes it possible to compare the absorption in different groups given different components of dietary fiber.