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Knowledge about nutrient intakes and sources can help put dietary advice into a practical context. Continued monitoring of top food sources of nutrients and nutrient contributions from fortification will be important.

In this paper we have described physiological factors that are likely to influence iron bioavailability, reviewed chemical properties of iron important to its absorption, and addressed the question posed in the title. Intestinal transit times, luminal pH, and diffusion barriers resulting from gastrointestinal mucus may affect absorption. The tendency of iron to form large-molecular-weight species and to bind to macromolecules may limit its absorption. Iron solubility following in vitro gastrointestinal digestion is a reliable predictor of ascorbic acid effects on bioavailability but not of protein effects. Solubility of low-molecular-weight iron is better than simple solubility for predicting iron bioavailability.

The objective of this work was to quantify the contribution of fortification (defined here as adding nutrients beyond traditional enrichment standards) to dietary nutrient intakes in the United States. A list of fortified foods was developed that was relevant at the time of the analyses, and prefortification (naturally occurring) nutrients in the fortified foods were determined from industry-supplied data. Using dietary data from the 1989-1991 Continuing Survey of Food Intakes by Individuals (CSFII), intakes of nine nutrients were determined both as reported in the CSFII (i.e., postfortification) and also by using prefortification nutrient levels for the identified fortified foods. We report data for the total population age >/= 1 y based on respondents (n = 11,710) with 3 d of dietary data, as well as select age/gender subgroups. All data were weighted. Fortification substantially increased the intakes of all nutrients examined except calcium, in all age/gender groups but especially in children. In numerous cases, fortification was responsible for boosting median or 25th percentile intakes from below to above the RDA. The breakfast cereal category was responsible for nearly all the intake of nutrients from fortified foods, except vitamin C for which juice-type beverages made as great or a greater contribution. These data from 1989 to 1991 serve as a useful baseline with which to compare contributions of fortification as the practice expands. The large contribution of fortification even in 1989-1991 suggests that continued monitoring of fortification practices, using methods such as those presented here, is important.

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Sodium alginate was dispersed in iron chelate solutions and incubated for 10 min. The alginate was precipitated with acetone and the iron in the supernatant measured. Bound iron was calculated. The effects of pH, iron:alginate ratio, chelator, and competing cation on iron binding by alginate were determined. Binding increased as the pH decreased and as the iron:alginate ratio increased; the chelator used (EDTA, NTA, ascorbic acid, citrate) affected complexing. Binding decreased in the presence of calcium. In vitro iron availability studies indicated that algmate-iron complexes are disrupted during digestion.