An algorithm to assess intestinal iron availability for use in dietary surveys

Abstract

In nutritional epidemiology, it is often assumed that nutrient absorption is proportional to nutrient intake. For several nutrients, including non-haem Fe, this assumption may not hold. Depending on the nutrients ingested with non-haem Fe, its availability for absorption varies greatly. Therefore, using Fe intake to examine associations between Fe and health can impact upon the validity of findings. Previous algorithms that adjust Fe intakes for dietary factors known to affect absorption have been found to underestimate Fe absorption and, in the present study, perform poorly on independent dietary data. We have designed a new algorithm to adjust Fe intakes for the effects of ascorbic acid, meat, fish and poultry, phytate, polyphenols and Ca, incorporating not only absorption data from test meals but also current understanding of Fe absorption. In so doing, we have created a robust and universal Fe algorithm with potential for use in large cohorts. The algorithm described aims not to predict Fe absorption but available Fe in the gut, a measure we believe to be of greater use in epidemiological research. Available Fe is Fe available for absorption from the gastrointestinal tract, taking into account enhancing or inhibiting effects of dietary modifiers. Our algorithm successfully estimated average Fe availability in test meal data used to construct the algorithm and, unlike other algorithms tested, also provided plausible predictions when applied to independent dietary data. Future research is needed to evaluate the extent to which this algorithm is useful in epidemiological research to relate Fe to health outcomes.

Iron status is inversely associated with dietary iron intakes in patients with inactive or mildly active inflammatory bowel disease

“…Abbreviations: IQR interquartile range; IBD inflammatory bowel disease; FFQ food frequency questionnaire; (1) Predicted from Rickard et al [7]. …”

“…available non-haem + available haem iron) because ‘available haem iron’ is typically ascribed a standard percentage (e.g. 25%) of total haem iron intake irrespective of other dietary variables [7]. Thus, in comparison between groups, total haem iron entirely reflects ‘available haem iron’, unlike the situation described herein for non-haem iron.…”

“…Estimated availability of dietary non-haem iron was calculated using the recently developed algorithm of Rickard et al [7] namely:…”

“…First, as part of a broader programme investigating iron intakes, absorption, and quality of life in patients with IBD, iron deplete and iron replete subjects could be genuinely separated, based upon absorption of iron from a single oral dose rather than conventional haematological parameters [4]. Secondly, using an iron-specific, validated food frequency questionnaire and a recently developed algorithm, we were able to calculate ‘available iron’ hence taking account of absorption modifiers of dietary iron as well as total dietary iron [6,7]. We also studied a control group of healthy individuals, thus determining whether our findings would be IBD-specific or reflected in the general population as well as providing a comparison group for the data.…”

In vivo and in vitro digestibility of the calcium contained in foods of animal and plant origin

“…All these factors make it difficult to determine and standardize the intestinal absorption of Ca, although the determination of Ca intestinal absorption is useful for improving the fulfillment of Ca requirements or the assessment of digestible Ca intake in epidemiologic survey as proposed by Rickard et al [21] for Fe.…”