Iron deficiency is the most common global nutritional problem, which can be attributed mainly due to poor dietary iron bioavailability. Although many methods exist in assessing bioavailability, they may not be applicable for large populations. Algorithms have therefore been developed from single meal studies for assessing iron bioavailability. However, based on exaggerated effect of dietary factors on iron absorption, new algorithms based on complete diet studies are needed. The objectives of these studies were to: (i) develop a new algorithm from complete diet studies data (manuscript 1); (ii) estimate iron absorption from the US diet using the new algorithm (manuscript 2); and (iii) investigate the effect of long-term phytate consumption on iron absorption (manuscript 3). We developed the algorithm using data from four complete diet studies in which nonheme iron absorption was measured in each subject for three different dietary periods. In estimating iron absorption from the US diet, we used the National Health and Nutrition Examination Survey (NHANES, 2001-2002), MyPyramid Equivalents Database (MPED), and the Food and Nutrient Database for Dietary Studies (FNDDS). In the third study, iron absorption from a high phytate test meal was measured using the area under the curve (AUC) for serum iron in female subjects with ferritin < 30 µg/L (n=28) before and after an eight week dietary modification with high (n=14) or low (n=14) phytate diets. In the first study, serum ferritin explained 35 % of the variability in iron absorption, whereas the effect of dietary factors was small. In the second study, iron bioavailability from the US diet was 15% compared to the currently used value of 18 %. The third study found a significant increase in absorption in the high phytate group (640 to 905 µmol/L; P < 0.05) and a non-significant decrease (337 to 267 µmol/L) in the low phytate group, indicating that the inhibitory effect of phytate on nonheme iron absorption is dampened among individuals who consume high phytate diet regularly. The findings of these studies have implications for iron nutrition policies for setting recommendations for iron intake and biofortification of high phytate staples with iron.