Different metabolic pathways of supplemental and fortification Fe, or inhibition of Zn absorption by Fe, may explain adverse effects of supplemental Fe in Fe-sufficient infants. We determined whether the mode of oral Fe administration or the amount habitually consumed affects Fe absorption and systemic Fe utilisation in infants, and assessed the effects of these interventions on Zn absorption, Fe and Zn status, and growth. Fe-sufficient 6-month-old infants (n 72) were randomly assigned to receive 6·6 mg Fe/d from a high-Fe formula, 1·3 mg Fe/d from a low-Fe formula or 6·6 mg Fe/d from Fe drops and a formula with no added Fe for 45 d. Fractional Fe absorption, Fe utilisation and fractional Zn absorption were measured with oral (57Fe and 67Zn) and intravenous (58Fe and 70Zn) isotopes. Fe and Zn status, infection and growth were measured. At 45 d, Hb was 6·3 g/l higher in the high-Fe formula group compared with the Fe drops group, whereas serum ferritin was 34 and 35 % higher, respectively, and serum transferrin 0·1 g/l lower in the high-Fe formula and Fe drops groups compared with the low-Fe formula group (all P<0·05). No intervention effects were observed on Fe absorption, Fe utilisation, Zn absorption, other Fe status indices, plasma Zn or growth. We concluded that neither supplemental or fortification Fe nor the amount of Fe habitually consumed altered Fe absorption, Fe utilisation, Zn absorption, Zn status or growth in Fe-sufficient infants. Consumption of low-Fe formula as the only source of Fe was insufficient to maintain Fe stores.

The aim of the present study was to analyse the sequence variability of the porcine Zip4-like Zn transporter gene and the association of identified sequence variants with average daily gain, apparent Zn absorption, plasma Zn concentration and Zn concentration in the liver and pancreas. For the purpose of the study, two different sample sets were used. Set one, which was used for sequencing and association analysis, included mRNA from intestinal tissue from thirty-five piglets of a feeding trial. Sample set two consisted of forty-six samples of genomic DNA from sperm or tissue of wild boars and several pig breeds and was used to genotype animals of different breeds. The sequence analysis of porcine Zip4-like complementary DNA in sample set one revealed the presence of seven nucleotide substitutions. Of these, six were synonymous, whereas a substitution of A with C in exon IX (XM_001925360 c.1430A>C) causes an amino acid exchange from glutamic acid to alanine (p.Glu477Ala). The association analysis revealed no influence of the six synonymous substitutions on Zn values, but the non-synonymous nucleotide exchange significantly increased Zn concentration in the pancreas and apparent Zn absorption of the piglets in week 2 of the feeding trial. The parentage of the piglets and the genotyping results in sample set two suggest a breed-specific presence of the A allele in Piétrain for this amino acid substitution. These results indicate that genotype influences the Zn absorption abilities of individual animals, which should be taken into consideration in animal breeding as well as for the selection of experimental animals.

A previously described mathematical model of Zn absorption as a function of total daily dietary Zn and phytate was fitted to data from studies in which dietary Ca, Fe and protein were also measured. An analysis of regression residuals indicated statistically significant positive relationships between the residuals and Ca, Fe and protein, suggesting that the presence of any of these dietary components enhances Zn absorption. Based on the hypotheses that (1) Ca and Fe both promote Zn absorption by binding with phytate and thereby making it unavailable for binding Zn and (2) protein enhances the availability of Zn for transporter binding, the model was modified to incorporate these effects. The new model of Zn absorption as a function of dietary Zn, phytate, Ca, Fe and protein was then fitted to the data. The proportion of variation in absorbed Zn explained by the new model was 0·88, an increase from 0·82 with the original model. A reduced version of the model without Fe produced an equally good fit to the data and an improved value for the model selection criterion, demonstrating that when dietary Ca and protein are controlled for, there is no evidence that dietary Fe influences Zn absorption. Regression residuals and testing with additional data supported the validity of the new model. It was concluded that dietary Ca and protein modestly enhanced Zn absorption and Fe had no statistically discernable effect. Furthermore, the model provides a meaningful foundation for efforts to model nutrient interactions in mineral absorption.

The Thriposha programme is a community-level nutrition intervention in Sri Lanka that provides a combination of energy, protein and micronutrients as a ‘ready-to-eat’ cereal-based food. We measured the bioavailability of Fe and Zn from Thriposha formula at two different molar ratios of Zn:Fe in order to determine the effect on Fe and Zn absorption. Children 4–7 years (n 53) were given a meal prepared with 50 g Thriposha containing 1·5 mg Zn as zinc sulphate and either 9 mg (high Fe concentration (HiFe)) or 4·5 mg (low Fe concentration (LoFe)) Fe as ferrous fumarate. Zn and Fe percent absorption were measured using stable isotopes by tracer:tracee ratio and by incorporation of erythrocytes, respectively. Percent Fe absorption from the two meals was similar (6·6 % (4·8) v. 4·8 % (2·6); P = 0·15), but total Fe absorption was significantly higher from the HiFe meal (0·59 (0·43) mg) than the LoFe meal (0·20 (0·12) mg; P = 0·01). There was no significant difference between the two groups in Zn absorption (10·7 % (0·9) v. 8·8 % (1·4), P = 0·13, respectively). Decreasing the amount of Fe in Thriposha did not cause a significant change in the percent absorption of Fe and Zn, but significantly lowered the total amount of absorbed Fe. These results demonstrate the utility of maintaining a higher Fe content in this supplement. Further studies to increase Zn content are warranted while maintaining a HiFe.

Few data have evaluated Zn balance in young children after the first year of life. The objective of the present study was to study the relationships among Zn intake, absorption, endogenous faecal excretion, and retention in a group of healthy children. Thirty children, aged 15–48 months, were studied on a diet representative of their usual daily mineral intake. Zn absorption was assessed using a dual-tracer stable-isotope technique. Endogenous Zn faecal excretion and Cu absorption were determined in a subset of children. We found that Zn intake from the in-patient weighed dietary record (5·0 (sd 2·1) mg/d) was significantly greater than the current estimated average requirement (EAR; 2·5 mg/d; P < 0·0001). Neither fractional Zn absorption, urinary Zn excretion, nor endogenous faecal Zn excretion was significantly related to Zn intake (r2 < 0·1; P>0·4, for all). Absolute Zn absorption was significantly related to Zn intake (r2 0·696; P < 0·0001), as was Zn retention (r2 0·506; P < 0·0001). Cu absorption was relatively high (75·1 (sd 10·8) %) despite the high Zn intake. The EAR for Zn based on this dataset would appear to be between 4·2 and 4·7 mg/d to allow for a net average retention of 120 μg/d consistent with growth needs. We concluded that at relatively high Zn intakes there was little evidence of down regulation of absorption or up regulation of urinary or endogenous faecal Zn excretion across the intake range studied. Zn retention was positively correlated with intake. A Zn intake between 4·2 and 4·7 mg/d should meet the requirement for normal growth for this age group.

We examined the effects of ingestion of five types of insoluble fibre on growth and Zn absorption in rats fed a marginally Zn-deficient diet (6·75 mg (0·103 mmol) Zn/kg diet) with or without added sodium phytate (12·6 mmol/kg diet). The types of insoluble fibre tested were corn husks, watermelon skin, yam-bean root (Pachyrhizus erosus) and pineapple core, and cellulose was used as a control (100 g/kg diet). Body-weight gain in the cellulose groups was suppressed by 57 % by feeding phytate. Body-weight gain in phytate-fed rats was 80 % greater in the watermelon skin fibre and yam-bean root fibre group than that in the cellulose group. Zn absorption ratio in the cellulose groups was lowered by 46 and 70 % in the first (days 7–10) and second (days 16–19) measurement periods with feeding phytate. In the rats fed the phytate-containing diets, Zn absorption ratio in the watermelon skin, yam-bean root and pineapple core fibre groups was 140, 80 and 54 % higher respectively than that in the cellulose group, in the second period. Fe absorption was not suppressed by phytate, however, feeding of these three types of fibre promoted Fe absorption in rats fed phytate-free diets. The concentration of soluble Zn in the caecal contents in the watermelon skin fibre or yam-bean root fibre groups was identical to that in the control group in spite of a higher short-chain fatty acid concentration and lower pH in the caecum. These findings indicate that ingestion of these types of insoluble fibre recovered the growth and Zn absorption suppressed by feeding a high level of phytate, and factors other than caecal fermentation may also be involved in this effect of insoluble fibre.

The objectives of this study were to confirm the non-absorbability and the reproducibility of faecal excretion kinetics of orally administered rare earth elements, and to investigate the excretion profiles of rare earth elements and stable isotopic tracers of Fe and Zn to establish the extent to which rare earth element markers duplicate the behaviour of isotopic tracers. Two investigations were performed: (1) six healthy subjects consumed a solution containing five rare earth elements in amounts varying from 1 to 10 mg; (2) seven healthy subjects were given a standard solution labelled with Sm marker and 57Fe tracer, and a meal labelled with Yb marker and 58Fe and 70Zn tracers. Individual faecal samples were collected and analysed to determine recoveries of rare earth elements and unabsorbed isotopic tracers. The mean values for recoveries were 94·1 (SD 4·5) % FOR THE FIVE RARE EARTH ELEMENTS, AND 103 (sd 3·0) % and 99·8 (sd 2·8) % for Sm and Yb respectively. For Fe consumed with the solution, excretion kinetics of the rare earth element marker and unabsorbed tracers with cumulative collections of the first two and three faecal samples were identical, but endogenous excretion of Fe was significant (P<0·05) in stools collected after the third. For Fe and Zn consumed with the meal, the excretion kinetics for the first two individual faecal samples and composites of sequential outputs were identical. Rare earth elements can be used as markers in studies of measurement of absorption. The dose of tracer required for the measurement of absorption would be reduced proportionally to the reduction of the period of faecal sampling, so that studies with stable isotopes would be more economical, thus enabling epidemiological investigations.

Zn absorption was investigated in healthy elderly subjects aged 71–78 years and in young subjects aged 23–43 years using serum concentration curve (SCC) tests. Both groups had similar Zn and protein status. The increase in serum Zn was monitored for 180 min after ingestion of 200ml of soya milk enriched with 50mg of Zn. Three levels of phytic acid were used: 0g/200ml (totally dephytinized soya milk), 0.13 g/200ml (half dephytinized), and 0.26 g/200ml (natural phytic acid content). In a first study the effect of 0 v. 0.26 g/200 ml phytic acid was compared in 10 elderly and 10 young subjects, each subject receiving both treatments. In a second study soya milks with 0 and 0.13 g/200ml were tested in nine elderly and ten young subjects, again receiving both treatments. Mean areas under the curve of the SCC tests conducted with the 0 g/200 ml soya milk were found to be the same in both studies. Phytic acid strongly depressed Zn absorption in both studies (P ≤ 0.05), but to a greater extent at the 0.26 g/200ml level. No difference was found between the groups of young and elderly subjects. Therefore, no significant effect of aging on Zn absorption, as evaluated by the SCC test, or on the inhibitory effect of phytic acid was detected.

Eleven fasted adult men consumed a chicken meat sandwich made with white or wholemeal bread, extrinsically labelled with 2 mg 67Zn, on two different occasions. Immediately after eating the sandwich they were given an intravenous injection of 1·5 mg 70Zn. True Zn absorption (which was approximately 7% higher than apparent absorption) was determined by the faecal balance technique by making an allowance for endogenous excretion from measurements of faecal excretion of 70Zn. There was no significant difference in mean true Zn absorption from the white or wholemeal bread sandwich, 33·6 and 25·4% respectively. It was concluded that the substitution of wholemeal for white bread does not reduce Zn absorption from meat-based sandwiches.

Intestinal brush-border-membrane vesicles were prepared from the porcine small bowel by magnesium precipitation and differential centrifugation, and were functionally intact. The influence of dietary ligands on 65Zn uptake was determined using a 65Zn concentration of 5 μm, an incubation time of 1 min and a reaction temperature of 27°, with a rapid filtration technique. At this low Zn concentration the addition of an excess of folate, histidine or glucose had no effect on Zn uptake. Addition of picolinate, citrate and phytate to the incubation medium significantly reduced Zn uptake at all concentrations of ligand examined. Any inhibitory effects of folic acid in vivo may thuss be due to a mucosal rather than lumen interaction. Those ligands inhibiting absorption may have done so through the formation of Zn-ligand complexes, which are either insoluble, or which reduce the binding of Zn to its mucosal receptor. This in vitro model of Zn absorption is useful for comparing the effects of potential Zn-binding ligands in the diet.

The addition of 1 g sugar-beet fibre (Beta Fibre) to 3 g semi-synthetic diet resulted in a 54% increase in iron and a 39% increase in zinc absorption in rats. The same amount of non-starch polysaccharides fed as wheat bran (1.9 g) had no effect on Fe absorption but reduced Zn absorption by 9%. The inhibitory effect of wheat bran is probably due to its high phytate content, but there is, as yet, no explanation for the enhancement of Fe and Zn absorption caused by Beta Fibre. If the effect also occurs in man, it will have important implications for high-fibre diets and mineral nutrition.