Estimation of Iron Bioavailability from the Diets of an Adolescent Population

Estimation of dietary iron bioavailability and determination of dietary iron intake were evaluated from 24-hour food records of 224 adolescents in eastern Tennessee. Total daily iron intakes, 16.1 mg for males and 11.1 mg for females, were below the Recommended Dietary Allowances (RDA). Application of the Monsen and Balintfy model to estimate iron bioavailability showed that absorbable iron from males' diets, 1.38 mg, and from females' diets, 0.91 mg, was below recommended levels. Percentages of bioavailable iron were below the assumed 10% absorption level,a criterion used in establishing the RDA for iron. Thus, total dietary iron was inadequate for males and females as indicated by both measures.

Patterns of iron bioavailability differed among eating occasions but were similar for males and females. Although intakes of the enhancing factor, ascorbic acid, were high at breakfast, the meal was lowest in total iron, percentages of bioavailable iron, and amounts of absorbable iron compared with other meals. The nutrient density of ascorbic acid and iron of lunch meals of adolescents did not meet recommended levels, but more meat, fish, and poultry foods were consumed at lunch than at breakfast. In comparison to other meals, evening meal patterns were highest in meat, fish, and poultry; total iron; total amounts of enhancing factors; amounts of absorbable iron; and percentages of bioavailable iron. Dietary patterns of adolescent males at the evening meal approached desirable patterns to maximize iron bioavailability. Intakes of iron and absorbable amounts of iron in adolescent females' diets were less than in males' diets and were inadequate.

Snacks, which were consumed frequently by adolescents, contributed substantial amounts of food energy but were low in total iron, absorbable iron, and bioavailable iron. The inclusion of ascorbic acid sources and animal tissue foods, enhancers of iron bioavailability, were low in snacks.

Further evaluation of dietary patterns of adolescents shows that some males and females exhibited patterns that contributed to desirable levels of absorbable iron. Ascorbic acid and meat, fish, and poultry foods were high in their diets. Mean iron intakes of adolescent males and females in this group exceeded or approached the RDA.

Adolescents whose iron intakes were inadequate may not be able to significantly improve iron adequacy through enhancement of iron absorption. They need to increase consumption of iron as well as enhancing factors. Application of the model to estimate iron bioavailability was useful in identifying patterns contributing to iron bioavailability.