Approaches used to estimate bioavailability when deriving dietary reference values for iron and zinc in adults

This review aims to describe approaches used to estimate bioavailability when deriving dietary reference values (DRV) for iron and zinc using the factorial approach. Various values have been applied by different expert bodies to convert absorbed iron or zinc into dietary intakes, and these are summarised in this review. The European Food Safety Authority (EFSA) derived zinc requirements from a trivariate saturation response model describing the relationship between zinc absorption and dietary zinc and phytate. The average requirement for men and women was determined as the intercept of the total absorbed zinc needed to meet physiological requirements, calculated according to body weight, with phytate intake levels of 300, 600, 900 and 1200 mg/d, which are representative of mean/median intakes observed in European populations. For iron, the method employed by EFSA was to use whole body iron losses, determined from radioisotope dilution studies, to calculate the quantity of absorbed iron required to maintain null balance. Absorption from the diet was estimated from a probability model based on measures of iron intake and status and physiological requirements for absorbed iron. Average dietary requirements were derived for men and pre- and post-menopausal women. Taking into consideration the complexity of deriving DRV for iron and zinc, mainly due to the limited knowledge on dietary bioavailability, it appears that EFSA has made maximum use of the most relevant up-to-date data to develop novel and transparent DRV for these nutrients

Reminiscences of my life as a nutritionist - and looking to the future

In this invited article for the Crystal Ball series, I have tried to briefly cover my undergraduate and post-graduate training and subsequent career in nutrition, and end with some thoughts about the future. It has not been possible to give a comprehensive account of my many years of nutrition research, so I have selected a few events that might amuse readers. Also, due to the lack of space, I have been unable to mention all the wonderful colleagues and friends with whom I have interacted, but, if they read this article, they know who they are. Unfortunately, a growing number are no longer with us and I would like to pay tribute to them and their important contribution to human nutrition

The role of meat in iron nutrition of vulnerable groups of the UK population

Iron deficiency is a common public health problem in the UK. This review examines the role of meat in iron nutrition, focusing on the most vulnerable groups of the UK population. Meat contains haem iron which is absorbed by a different pathway to non-haem iron found in cereals and vegetables. A summary of absorption data from studies using isotopically-labelled haem iron shows that, although there is a wide degree of variation, haem iron bioavailability is consistently higher than non-haem iron. The importance of meat alternatives, such a plant protein, insects, and biofortified crops as a supply of bioavailable iron, and the use of food iron fortification is reviewed. Finally, the consequences of excluding meat from the diet in relation to dietary iron requirements is discussed

Dietary factors modulate iron uptake in Caco-2 cells from an iron ingot used as a home fortificant to prevent iron deficiency

Iron deficiency is a major public health concern and nutritional approaches are required to reduce its prevalence. The aim of this study was to examine the iron bioavailability of a novel home fortificant, the "Lucky Iron Fish™" (LIF) (www.luckyironfish.com/shop, Guelph, Canada) and the impact of dietary factors and a food matrix on iron uptake from LIF in Caco-2 cells. LIF released a substantial quantity of iron (about 1.2 mM) at pH 2 but this iron was only slightly soluble at pH 7 and not taken up by cells. The addition of ascorbic acid (AA) maintained the solubility of iron released from LIF (LIF-iron) at pH 7 and facilitated iron uptake by the cells in a concentration-dependent manner. In vitro digestion of LIF-iron in the presence of peas increased iron uptake 10-fold. However, the addition of tannic acid to the digestion reduced the cellular iron uptake 7.5-fold. Additionally, LIF-iron induced an overproduction of reactive oxygen species (ROS), similar to ferrous sulfate, but this effect was counteracted by the addition of AA. Overall, our data illustrate the major influence of dietary factors on iron solubility and bioavailability from LIF, and demonstrate that the addition of AA enhances iron uptake and reduces ROS in the intestinal lumen

Modeling tool for calculating dietary iron bioavailability in iron-sufficient adults

Background: Values for dietary iron bioavailability are required for setting dietary reference values. These are estimated from predictive algorithms, nonheme iron absorption from meals, and models of iron intake, serum ferritin concentration, and iron requirements. Objective: We developed a new interactive tool to predict dietary iron bioavailability. Design: Iron intake and serum ferritin, a quantitative marker of body iron stores, from 2 nationally representative studies of adults in the United Kingdom and Ireland and a trial in elderly people in Norfolk, United Kingdom, were used to develop a model to predict dietary iron absorption at different serum ferritin concentrations. Individuals who had raised inflammatory markers or were taking iron-containing supplements were excluded. Results: Mean iron intakes were 13.6, 10.3, and 10.9 mg/d and mean serum ferritin concentrations were 140.7, 49.4, and 96.7 mg/L in men, premenopausal women, and postmenopausal women, respectively. The model predicted that at serum ferritin concentrations of 15, 30, and 60 mg/L, mean dietary iron absorption would be 22.3%, 16.3%, and 11.6%, respectively, in men; 27.2%, 17.2%, and 10.6%, respectively, in premenopausal women; and 18.4%, 12.7%, and 10.5%, respectively, in postmenopausal women. Conclusions: An interactive program for calculating dietary iron absorption at any concentration of serum ferritin is presented. Differences in iron status are partly explained by age but also by diet, with meat being a key determinant. The effect of the diet is more marked at lower serum ferritin concentrations. The model can be applied to any adult population in whom representative, good-quality data on iron intake and iron status have been collected. Values for dietary iron bioavailability can be derived for any target concentration of serum ferritin, thereby giving risk managers and public health professionals a flexible and transparent basis on which to base their dietary recommendations. This trial was registered at clinicaltrials.gov as NCT01754012