Comparison of complementary feeding strategies to meet zinc requirements of older breastfed infants

BACKGROUND

The low zinc intake from human milk at ∼6 mo of age predicts the dependence on complementary foods (CF) to meet the zinc requirements of older breastfed-only infants.

OBJECTIVE

The objective of this study was to compare major variables of zinc homeostasis and zinc status in 9-mo-old breastfed infants who were randomly assigned to different complementary food regimens.

DESIGN

Forty-five exclusively breastfed 5-mo-old infants were randomly assigned to receive commercially available pureed meats, iron-and-zinc-fortified infant cereal (IZFC), or whole-grain, iron-only-fortified infant cereal (IFC) as the first and primary CF until completion of zinc metabolic studies between 9 and 10 mo of age. A zinc stable-isotope methodology was used to measure the fractional absorption of zinc (FAZ) in human milk and CF by dual-isotope ratios in urine. Calculated variables included the dietary intake from duplicate diets and 4-d test weighing, the total absorbed zinc (TAZ) from FAZ × diet zinc, and the exchangeable zinc pool size (EZP) from isotope enrichment in urine.

RESULTS

Mean daily zinc intakes were significantly greater for the meat and IZFC groups than for the IFC group (P < 0.001); only intakes in meat and IZFC groups met estimated average requirements. Mean (±SEM) TAZ amounts were 0.80 ± 0.08, 0.71 ± 0.09, and 0.52 ± 0.05 mg/d for the meat, IZFC, and IFC groups, respectively (P = 0.027). Zinc from human milk contributed <25% of TAZ for all groups. The EZP correlated with both zinc intake (r = 0.43, P < 0.01) and TAZ (r = 0.54, P < 0.001).

CONCLUSION

Zinc requirements for older breastfed-only infants are unlikely to be met without the regular consumption of either meats or zinc-fortified foods.

Infant stunting is associated with short maternal stature

The objectives were to determine the range of maternal height associated with growth velocity of older infants and the magnitude of this association in an indigent population. Maternal height and infant length-for-age z scores (LAZ) were positively correlated at both 6 (n = 412, r = 0.324) and 12 (n = 388, r = 0.335) months (P < 0.0001) and for maternal heights from 131 to 164  cm. Maternal height is independently associated with infant LAZ and stunting (LAZ <-2) at both 6 and 12 months (P < 0.001) and with linear growth velocity from 6 to 12 months (P = 0.0023).

The use of dysprosium to measure endogenous zinc excretion in feces eliminates the necessity of complete fecal collections

The secretion of endogenous zinc (Zn) into the gut and subsequent excretion in the feces is understood to play a major role in maintaining Zn homeostasis in humans. Therefore, the measurement of endogenous Zn losses in the feces (EFZ) can be an important aspect of the study of Zn metabolism and homeostasis. The methods currently used to measure EFZ have the disadvantage of requiring complete fecal collections over multiple days. We have investigated the use of dysprosium (Dy), a nonabsorbable rare earth metal, in a method of determining EFZ that does not require complete fecal collections and permits the measurement of EFZ from several fecal samples. The method was evaluated using data from a study of free-living adult females in which Dy was administered 3-4 times/d over a period of 5 or 6 d to monitor completeness of fecal collections. The results did not differ from those obtained using an established isotope dilution method. We found that the measurement of the sample Dy:Zn ratio was useful for selecting samples for measurement. We conclude that the Dy method of determining EFZ is a valid and less burdensome alternative to current techniques.

Neither a zinc supplement nor phytate-reduced maize nor their combination enhance growth of 6- to 12-month-old Guatemalan infants

After age 6 mo, the combination of breast-feeding and unfortified plant-based complementary feeding provides inadequate zinc (Zn). Additionally, high phytate intakes compromise the bioavailability of zinc. Our principal objective in this randomized controlled, doubly masked trial was to determine the effect of substituting low-phytate maize, a daily 5-mg zinc supplement, or both, in infants between ages 6-12 mo on impaired linear growth velocity, a common feature of zinc deficiency. In the Western Highlands of Guatemala, 412 infants were randomized to receive low-phytate or control maize. Within each maize group, infants were further randomized to receive a zinc supplement or placebo. Length, weight, and head circumference were measured at 6, 9, and 12 mo of age. There were no significant differences between the 2 maize groups or between the Zn supplement and placebo groups and no treatment interaction was observed for length-for-age (LAZ), weight-for-length (WLZ) or head circumference Z-scores. Overall mean (+/- SD) Z-scores at 6 mo for combined treatment groups were: LAZ, -2.1 +/- 1.1; WLZ, 0.7 +/- 1.0; and head circumference Z-score, -0.7.0 +/- 1.0. At 12 mo, these had declined further to: LAZ, -2.5 +/- 1.1; WLZ, -0.0 +/- 0.9; and head circumference Z-score, -0.9 +/- 1.1; 83.3% were stunted and 2% were wasted. Low linear growth in older Guatemalan infants was not improved with either low-phytate maize or a daily 5-mg zinc supplement. Low contribution of maize to the complementary food of the infants negated any potential advantage of feeding low-phytate maize.

Zinc bioavailability and homeostasis

Zinc has earned recognition recently as a micronutrient of outstanding and diverse biological, clinical, and global public health importance. Regulation of absorption by zinc transporters in the enterocyte, together with saturation kinetics of the absorption process into and across the enterocyte, are the principal means by which whole-body zinc homeostasis is maintained. Several physiologic factors, most notably the quantity of zinc ingested, determine the quantity of zinc absorbed and the efficiency of absorption. Other factors are age and the time over which zinc is ingested. Zinc from supplements has not been shown to be absorbed differently from that taken with meals that lack inhibitors of zinc absorption. The principal dietary factor known to impair zinc bioavailability is inositol hexa- (and penta-) phosphate or phytate. Modeling of zinc absorption as a function of dietary zinc and phytate accounts for >80% of the variability in the quantity of zinc absorbed. Fitting the model to new data has resulted in continual improvement in parameter estimates, which currently indicate a maximal absorption in adults of approximately 6 mg Zn/d and that the average estimated dietary requirement doubles with 1000 mg dietary phytate/d. Intestinal excretion of endogenous zinc is regulated in response to recent absorption and to zinc status. The quantitative relation of intestinal excretion of endogenous zinc to zinc absorption is currently considered to be of major importance in the determination of zinc requirements. The effects of phytate on intestinal losses of endogenous zinc merit further investigation but are probably not of the same magnitude as its inhibitory effects on absorption of exogenous zinc.

Measurement of zinc absorption from meals: comparison of extrinsic zinc labeling and independent measurements of dietary zinc absorption

BACKGROUND

Extrinsic labeling techniques are typically used to measure fractional absorption of zinc (FAZ(extrinsic)) but none have been adequately evaluated.

OBJECTIVE

To compare determination of the quantity of zinc absorbed (TAZ(extrinsic)) using measurements of FAZ(extrinsic) with results of simultaneous determinations of dietary zinc absorbed (TAZ(metabolic)) that are not dependent on labeling ingested food with an extrinsic tracer (modified metabolic balance technique).

DESIGN

(70)Zn was administered orally with all meals for 6 consecutive days to 21 healthy, free-living adult women consuming a constant diet. (68)Zn and (67)Zn were administered intravenously. FAZ(extrinsic) was measured using a dual isotope tracer ratio technique and multiplied by dietary zinc to give TAZ(extrinsic). TAZ(metabolic) was determined by addition of net absorption of zinc and endogenous fecal zinc, the latter determined by an isotope dilution technique.

RESULTS

TAZ(extrinsic) and TAZ(metabolic) were 3.0 +/- 1.1 mg/day and 3.1 +/- 1.1 mg/day respectively, paired t-test p = 0.492. The correlation coefficient for TAZ(extrinsic) and TAZ(metabolic) was 0.91, and for FAZ(extrinsic) and FAZ(metabolic) was 0.95. A Bland Altman analysis indicated a bias of 0.07, and the limits of agreement of -0.86 to 1.01 for TAZ(extrinsic) and TAZ(metabolic).

CONCLUSION

These results from two independent methods provide reasonable validation of our extrinsic labeling technique for a wide range of composite diets.

Dietary reference intakes for zinc may require adjustment for phytate intake based upon model predictions

The quantity of total dietary zinc (Zn) and phytate are the principal determinants of the quantity of absorbed Zn. Recent estimates of Dietary Reference Intakes (DRI) for Zn by the Institute of Medicine (IOM) were based on data from low-phytate or phytate-free diets. The objective of this project was to estimate the effects of increasing quantities of dietary phytate on these DRI. We used a trivariate model of the quantity of Zn absorbed as a function of dietary Zn and phytate with updated parameters to estimate the phytate effect on the Estimated Average Requirement (EAR) and Recommended Daily Allowance for Zn for both men and women. The EAR predicted from the model at 0 phytate was very close to the EAR of the IOM. The addition of 1000 mg phytate doubled the EAR and adding 2000 mg phytate tripled the EAR. The model also predicted that the EAR for men and women could not be attained with phytate:Zn molar ratios > 11:1 and 15:1, respectively. The phytate effect on upper limits (UL) was predicted by first estimating the quantity of absorbed Zn corresponding to the UL of 40 mg for phytate-free diets, which is 6.4 mg Zn/d. Extrapolation of the model suggested, for example, that with 900 mg/d phytate, 100 mg dietary Zn is required to attain 6.4 mg absorbed Zn/d. Experimental studies with higher Zn intakes are required to test these predictions.

Inadequate intakes of dietary zinc among pregnant women from subsistence households in Sidama, Southern Ethiopia

Objective

To assess the prevalence of zinc inadequacy based on dietary intakes and plasma zinc concentrations and, simultaneously, the prevalence of inadequate intakes of energy, protein, calcium and iron.

Design

A cross-sectional study of a convenience sample of subsistence farming households in Sidama, Southern Ethiopia.

Subjects

Dietary intakes were calculated from 1-day weighed food records and 40 repeats from 99 pregnant women in the third trimester using analysed values of major staple foods for zinc, iron, calcium and phytate. The distribution of observed intakes was adjusted for usual intakes and the prevalence of inadequacy estimated using the estimated average requirement (EAR) cutpoint method. Prevalence of inadequacy for zinc, protein and iron intakes were compared with those based on biochemical measures.

Results

Prevalence of zinc inadequacy was very high: 99% for US FNB EAR and 100% for IZiNCG EAR compared to 72% based on low plasma zinc concentrations. Corresponding prevalence estimates for iron were much lower: 4% for inadequate intakes based on US FNB EAR vs. 8.7% for iron deficiency anaemia (haemoglobin < 110 g l−1; ferritin < 12 μg l−1) and 32.3% for low storage iron. Prevalence of inadequacy for protein was 100% for adjusted intakes and 91% for serum albumin < 32 g l−1. For calcium, 74% were at risk for inadequate intakes.

Conclusion

The high prevalence of inadequate intakes of zinc and protein was reasonably consistent with those based on biochemical measures. Such dietary deficits could be overcome by regular consumption of cellular animal protein. In contrast, both dietary and biochemical measures of iron inadequacy were low.

Zinc, gravida, infection, and iron, but not vitamin B-12 or folate status, predict hemoglobin during pregnancy in Southern Ethiopia

The etiology of anemia during pregnancy in rural Southern Ethiopia is uncertain. Intakes of animal-source foods are low and infections and bacterial overgrowth probably coexist. We therefore measured the dietary intakes of a convenience sample of Sidama women in late pregnancy who consumed either maize (n = 68) or fermented enset (Enset ventricosum) (n = 31) as their major energy source. Blood samples were analyzed for a complete blood count, vitamin B-12 and folate status, plasma ferritin, retinol, zinc, albumin, and C-reactive protein (CRP). The role of infection and gravida was also examined. Dietary intakes were calculated from 1-d weighed records. No cellular animal products were consumed. Of the women, 29% had anemia, 13% had iron deficiency anemia, 33% had depleted iron stores, and 74 and 27% had low plasma zinc and retinol, respectively. Only 2% had low plasma folate (< 6.8 nmol/L) and 23% had low plasma vitamin B-12 (< 150 pmol/L), even though 62% had elevated plasma methylmalonic acid (MMA) (> 271 nmol/L). None had elevated plasma cystathionine or total homocysteine (tHcys). Women with enset-based diets had higher (P = 0.052) plasma vitamin B-12 concentration and lower (P < 0.05) cell volume, plasma cystathionine, and retinol than women consuming maize-based diets, but mean hemoglobin, plasma ferritin, MMA, tHcys, and folate did not differ. Plasma zinc, followed by CRP (< or = 5 mg/L), gravida (< or = 4), and plasma ferritin (> or = 12 microg/L) status were major positive predictors of hemoglobin. Despite some early functional vitamin B-12 deficiency, there was no macrocytic anemia. Consumption of fermented enset may have increased vitamin B-12 levels in diet and plasma.

Intestinal excretion of endogenous zinc in Guatemalan school children

The intestine is the major route of excretion of endogenous zinc (Zn) and has a key role in maintaining Zn homeostasis. The principal objective of this paper is to provide an interpretative report of quantities of endogenous fecal Zn (EFZ) excreted by rural Guatemalan school children fed either normal or low phytate maize as their principal food staple. EFZ was measured by a Zn stable isotope technique. EFZ did not differ between control and low phytate maize groups. The overall EFZ (n = 53) was (mean +/- SD) 1.56 +/- 0.69 mg Zn/d or 0.07 +/- 0.03 mg Zn x kg body wt(-1) x d(-1). EFZ was not correlated with the quantity of Zn absorbed. The estimated EFZ at the level of absorption that matched the physiologic requirement (EFZ(PR)) did not differ from the above mean value. The EFZ(PR) of 0.07 +/- 0.03 mg Zn/kg body wt is twice the value currently used in the estimation of Dietary Reference Intakes. Supported by other recent childhood data, these results suggest that the current estimates of EFZ(PR) used in the calculation of Zn requirements for children are misleadingly low.

Zinc absorption during late pregnancy in rural southern Ethiopia

BACKGROUND

Little is yet known about zinc absorption in late pregnancy, and no information on absorption from the total diet is available.

OBJECTIVE

The objective was to measure the fractional absorption of zinc (FAZ) and to estimate the total quantity of absorbed zinc (TAZ) each day during the third trimester of pregnancy in poor rural southern Ethiopian women.

DESIGN

The participants (n = 17) were a convenience sample from a larger study population. The third stage of pregnancy was estimated from fundal height by the Bushulo Health Center prenatal outreach program. FAZ was determined with a dual-isotope tracer ratio technique that uses measurements of urine enrichment with zinc stable isotopes administered intravenously and orally, as an extrinsic label, with all meals in 1 d. Total dietary zinc (TDZ) was calculated from weighed diet records and Ethiopian food-composition tables supported by zinc and phytate analyses of major food items for individual meals. Plasma zinc and exchangeable zinc pool size were also estimated.

RESULTS

Mean (+/-SD) FAZ was 0.35 +/- 0.11, TDZ was 6.0 +/- 3.2 mg/d, TAZ was 2.1 +/- 1.0 mg/d, phytate intake was 1033 +/- 843 mg/d, plasma zinc was 44.1 +/- 6.0 microg/dL, and the exchangeable zinc pool size was 142 +/- 39 mg. The molar ratio of phytate to zinc was 17:1.

CONCLUSIONS

Women from a poor rural population who were dependent on a moderately high-phytate diet had low TDZ and low plasma zinc concentrations in the third trimester of pregnancy. TAZ was modestly higher than that predicted but did not meet physiologic requirements.

Changes in zinc absorption during development

Zinc (Zn) nutrition is of special practical importance in infants and young children, however relatively little is known about maturation and comparative aspects of Zn absorption. The principal objective of this paper is to compare Zn absorption of term infants, preterm infants, and adults on low phytate diets. Existing data derived from using Zn stable isotopes as extrinsic labels for an entire day were modeled with saturation kinetic analysis (saturable response model). When adjusted for differences in length of small intestine, the efficiency of Zn absorption for both term (4 months) and preterm (33 weeks post-conception) infants was comparable with that for adults, suggesting early maturation of mechanisms that regulate absorption. However, infant intestinal lengths were shorter, and Zn absorptive capacity was proportionately less. Reduced capacity was matched by lower Zn requirements for normal term infants. This favorable match, however, did not occur in the preterm infant because of relatively high Zn requirements. Although intestinal conservation of endogenous Zn in these preterm infants was appropriate in relation to the quantity of Zn absorbed, it was not optimal for achieving the retention required. Normal homeostatic mechanisms in the premature infant prevented efficient absorption of the quantity of Zn required or/and optimal conservation of endogenous Zn.

Effect of maternal consumption of lactobacillus GG on transfer and establishment of fecal bifidobacterial microbiota in neonates

BACKGROUND

Establishment of the gut microbiota at birth provides a substantial source of microbial stimuli for the maturation of the immune system. Deviations in this process precede the development of specific diseases providing the rationale for the use of probiotics to counteract them.

OBJECTIVE

This study was designed to characterize both the mother-infant bifidobacteria transfer at birth and the development of bifidobacteria microbiota during the first weeks of life in infants whose mothers received Lactobacillus rhamnosus GG or placebo.

METHODS

Species-specific PCR was used to assess the fecal bifidobacterial composition of mothers before and after delivery and in infants at 5 days and 3 weeks of age.

RESULTS

Bifidobacterium longum was the species most commonly found in the mothers. Bifidobacterium catenulatum was the most prevalent group in infants at 5 days of age and B. longum the predominant species at 3 weeks. At 5 days of age, infants whose mothers received L. rhamnosus GG showed a significantly higher occurrence of B. breve and lower of B. adolescentis than those from the placebo group. In addition, L. rhamnosus GG consumption increased the bifidobacterial diversity in infants and reduced the Bifidobacterium microbiota similarity between mother and infant.

CONCLUSIONS

These results indicate that specific changes in the transfer and initial establishment of bifidobacteria in neonates take place as consequence of the consumption of L. rhamnosus GG by the mothers.