At what age should breastfed infants be offered complementary foods group of answer choices?

Abstract

Complementary feeding, specifically the food choices that should be considered for meeting the nutritional needs of infants and toddlers, is a topic undergoing recent scientific scrutiny. The primary focus of the evidence in this review is for infants aged 6–24 mo who are continuing with breast-feeding with no or minimal formula supplementation. Some of the clinical factors for both infants and their mothers that influence infant nutrient requirements are discussed, as are the basis for emphasis on certain nutrients important for complementary feeding and possible strategies to meet nutrient needs for breast-fed infants. This article considers 2 micronutrients of particular concern, iron and zinc, with the emphasis on the latter, because iron is the focus of another article in this series. In terms of meeting micronutrient needs, breast-fed infants and formula-fed infants need to be addressed separately. Meeting the nutritional requirements of partially breast-fed infants is of particular concern, whereas formula-fed infants tend to meet their micronutrient requirements because of the high fortification levels of essential micronutrients in commercial infant formulas. Infants receiving only partial formula feeding, or inappropriately diluted formulas, may also be at risk for micronutrient deficiencies, but specifics are difficult to predict.

Clinically relevant factors

Interventions to prevent child deaths.

Bryce et al. (1) and Jones et al. (2) reviewed many simple interventions proposed to be efficacious worldwide in preventing childhood deaths under 5 y of age. Approximately 31% of the total estimated child deaths might be prevented by nutritional interventions such as exclusive breast-feeding for the first 6 mo, continued breast-feeding after 6 mo concurrent with appropriate complementary feeding, zinc supplementation (or adequate zinc intake), and vitamin A supplementation (Fig. 1). Zinc and vitamin A supplementation were highlighted because of accumulating evidence of the benefit of correcting deficiencies of these nutrients to early child health. Zinc is particularly important in relation to complementary feeding and breast-feeding.

Figure 1

Percentage of preventable childhood deaths under 5 y of age attributable to implementing simple, efficacious interventions worldwide. PROM, premature rupture of membranes. Information derived from Bryce et al. (1), Jones et al. (2), and the Global Health Council (3).

In addition to nutritional interventions, basic neonatal care is another major strategy to prevent avoidable deaths. Newborns are especially vulnerable to early morbidity and mortality. Simple interventions such as temperature management, antibiotics for premature rupture of membranes, ante natal steroids, and clean delivery are necessary. Malaria prevention and vaccinations will also contribute to reducing a substantial number of preventable childhood deaths worldwide. Another one-third of avoidable childhood deaths could be prevented if efficacious therapy were provided for treatable diseases (1–3) (Fig. 1).

Host factors affecting nutrient requirements.

Initially, the infant is highly dependent on his/her nutritional status at birth. The infant's birth weight and birth status will influence his/her nutritional requirements. Suboptimal birth status, e.g., prematurity or small-for-gestational age (SGA),3 has implications for nutrient requirements because neonatal stores of nutrients are affected if the infant is born prematurely. Normally, a large portion of nutrients is incorporated into the growing fetus during the last trimester of pregnancy. If this critical accretion period is cut short, the child will be born with lower reserves of some nutrients. For example, evidence is accumulating that SGA infants are particularly vulnerable to zinc deficiency, perhaps resulting from abnormal placental transfer of zinc to the fetus. Preliminary data suggest a deficit in the SGA infant's overall zinc reserves at birth, presenting a potential disadvantage for growth, development, and overall health (4).

A report by Sazawal et al. (5) underscores the vulnerability of SGA infants to zinc deficiency. In this study, 581 full-term SGA infants in India were given daily zinc supplements of 5 mg as sulfate during the first year of life. Zinc supplementation resulted in a reduction in mortality by two-thirds up to the 284th day of life compared with 573 others who were not given zinc supplements. These results suggest that SGA infants are particularly vulnerable to zinc deficiency in the first year of life and respond positively to zinc supplementation. In this study, ∼44% of all infants were exclusively breast-fed, 22% were predominantly breast-fed, 12.5% were partially breast-fed, and 20% were not breast-fed. In an analysis that included breast-feeding as a covariate, breast-feeding and intensity of breast-feeding provided a significant protective effect from mortality independent of zinc supplementation.

As another example of a host factor, Dr. Georgieff's group has demonstrated that infants of diabetic mothers are born with lower blood concentrations of ferritin and lower iron reserves, perhaps from inadequate placental transfer. There appear to be functional outcome differences for these infants in that they exhibit altered iron requirements and metabolism (6–8). The iron endowment of infants at birth is a host factor that is potentially modifiable by delayed cord clamping at delivery, the safety and feasibility of which is currently being investigated (9).

Postnatal growth typically exacts a high demand on nutrients such as iron and zinc. Hence, the rate of growth and an infant's need for catch-up growth will drive nutritional requirements to some extent. After delivery, neonatal reserves of iron are depleted sooner in preterm infants than in full-term infants. For the preterm infant, the requirement for an exogenous source of iron beyond what is available in breast milk is required sooner than for full-term infants (10).

Infants who are born in environments where there is a high infectious burden are expected to have increased nutrient losses, such as zinc loss through diarrhea. Moreover, nearly every bout of illness is accompanied by a period of some anorexia and poor intake. Infants who are subjected to recurrent infections and repeated cycles of illness simply are not afforded an opportunity for their growth to catch up.

For many developing countries, particularly in Asia, a substantial percentage of all infant deliveries result in SGA but near-term infants. Hence, because poor nutritional status, particularly poor micronutrient status, is a harbinger of early morbidity and mortality, maternal and infant nutrition is a critical area deserving of intervention to curb the prevalence of SGA infants and to bolster their nutritional status.

Maternal factors affecting nutrient requirements of infants.

Maternal status may affect an infant's nutrient reserves at birth and the composition of mother's milk for infant feeding. In general, the maternal diet can influence the vitamin content of milk but has little impact on mineral content.

In discussing maternal factors, it is important to recognize that the composition of human milk differs by time elapsed postpartum. For example, results from a longitudinal study of expressed milk from >70 well-nourished lactating women in Denver demonstrated a striking decline of zinc concentration in milk during the first 3 mo postpartum, followed by a more gradual decline thereafter (11). Among these women, those who were supplemented with 15 mg of zinc daily for 7 mo exhibited a significant decline in milk zinc concentrations over the course of the study that was similar to the change over time in the placebo group. Zinc supplementation made no significant impact on the zinc concentration of the milk. In China, healthy women with dietary zinc intakes approximately one-half of that of women in the United States have milk zinc concentrations at 2 mo postpartum that are similar to those of U.S. women (12). Evidence is mounting that undernourished women with lower intakes of zinc have similar patterns of zinc milk concentration as well, although randomized intervention trials of zinc supplementation are lacking in these populations. Malnourished women in Ethiopia with very low dietary zinc intakes are nevertheless able to sustain their milk zinc concentrations at levels comparable to those of U.S. women at 7 mo postpartum (13). Similarly, working Honduran women who have marginal nutritional status are also able to maintain zinc milk concentrations essentially equal to those of U.S. women at 9 mo postpartum (14). Thus, homeostatic mechanisms may enable the mother to produce zinc-sufficient milk despite less than optimal maternal nutrition. At present, the mechanisms controlling the physiologic decline of zinc concentration in milk over time are not fully understood.

Protein concentration in human milk also shows an accelerated decline in the first month postpartum, then levels off until after 4 mo postpartum, after which time there is a very gradual decline. In contrast to zinc and protein, iron concentrations show only a slight decline during the first month postpartum, and then milk concentrations are maintained at relatively consistent levels. The concentration of iron in human milk is relatively low compared with the infant's requirements for growth in the first year of life. Hence, the infant is dependent on being born with sufficient iron reserves to draw on initially and on receiving a substantial amount of iron from food sources later in this period (15).

Zinc and breast-fed infants

According to WHO, exclusive breast-feeding is generally adequate for the first 6 mo of life (16). Thereafter, mother's milk alone cannot be expected to provide all the micronutrients needed for the growing infant. Nutrients that have been identified as potentially “problematic” for breast-fed infants after 6 mo of age are iron, zinc, vitamin A, and vitamin B-6. Vitamin B-6 concentration in milk is influenced by the maternal diet, so if the mother's diet is adequate, the milk concentrations are likely to be adequate.

Iron and zinc are critical for immune function, neurocognitive development, and postnatal growth. As noted above, milk concentrations of these micronutrients are relatively resistant to the maternal diet. Hence, the breast-fed infant is particularly dependent on complementary foods containing iron and zinc after 6 mo of age. Without consistent intake of these micronutrients from complementary foods or other sources, the infant may develop physiologic manifestations of micronutrient deficiency.

Estimated zinc requirements and recommended intake.

For an exclusively breast-fed 7-mo-old infant, breast milk provides ∼0.5 mg of zinc, and a little over half of that is absorbed by the infant. Adding some cereal can increase zinc intake a slight amount but will fall short of providing the estimated physiologic requirement of 836 μg/d (17). Accounting for bioavailability and interindividual variability, the Institute of Medicine (IOM) calculated an estimated average requirement (EAR) of 2.5 mg/d for infants 7–12 mo of age. This amount of zinc cannot be supplied by breast milk alone after the early months post-partum.

The infant has limited adaptive mechanisms to compensate for modest zinc intake. Several researchers have studied the infant's ability to alter the percentage of zinc absorbed (i.e., increase efficiency for zinc absorption as the amount of zinc ingested decreases). However, if total intake is consistently inadequate, the child's nutritional status will falter. It has been estimated that complementary foods need to provide >90% of the recommended intake of 3 mg/d zinc for 9- to 11-mo-old infants (18,19). Hence, one criterion for the selection of complementary foods is that they be rich sources of zinc, as well as of iron.

Limited evidence is available indicating that breast-fed infants become zinc deficient under certain circumstances. Internationally, the majority of studies of zinc supplementation have examined the effects of supplementation on diarrhea and pneumonia across a wide age range, typically between 6 mo and 3 y. One study conducted in Ethiopia specifically focused on the 6- to 12-mo age range for breast-fed infants who were getting complementary foods that were primarily cereal-based (20). Infants were stratified by whether or not they were stunted and were randomly assigned to receive a placebo or 10 mg/d of zinc (as sulfate) for 6 d per week for 6 mo. In terms of length-for-age, infants who were stunted at the start of the study had a 2.5 times greater rate of linear growth with supplementation than the placebo group (P < 0.001). Weight gain by stunted infants was 80% greater after supplementation than after placebo (P < 0.001). Those that were not stunted also had significant improvement in their linear growth (P < 0.01) and weight gain (P < 0.05) from supplementation compared with placebo. Because zinc supplementation does not have any pharmacologic effect on growth, it is likely that these 6- to 12-mo-old breast-fed infants in Ethiopia were zinc deficient.

Findings for breast-fed U.S. infants' zinc intake from milk and complementary food at 7 mo of age also suggest potential for inadequacy (21,22). Mothers in the United States typically initiate complementary foods using rice cereal. Although some infant cereals are now zinc fortified, the adequacy of the fortification levels has not been studied, and many products are not fortified.

Some apparently healthy breast-fed U.S. infants do exhibit biochemical signs of suboptimal zinc and iron status. In a recently published study, exclusively breast-fed infants were randomized to receive either pureed beef or iron-fortified rice cereal as their first complementary food, which was started after 5 mo of age and continued until 7 mo of age (22). Because most infants did not begin complementary feeding until 6 mo of age, results reflect differences resulting from 1 mo of feeding. Those in the meat group consumed, on average ± SE, 1.9 ± 0.2 mg/d of zinc, and those in the cereal group consumed 0.6 ± 0.1 mg/d. Zinc and protein intakes at 7 mo were correlated with head-circumference growth from 7 to 12 mo, which was significantly greater in the meat group. There were no differences in linear or ponderal growth between groups. At 9 mo of age, after treatment interventions had ended, and unrelated to feeding group assignment, 36% of the infants had low plasma zinc levels (<9.9 μmol/L), and 30–40% had low plasma ferritin levels, reflecting exhaustion of their iron stores.

Stable isotope studies were conducted on a subgroup of 19 of these infants to examine the size of the exchangeable zinc pool (23). At 7 mo of age for the combined groups, the size of the exchangeable zinc pool was correlated with mean daily zinc intake (r = 0.72, P < 0.01). Because of wide variation in intake of the assigned complementary food, and thus in zinc intake, the size of the exchangeable zinc pool did not differ between meat and cereal groups.

Complementary feeding

History of complementary feeding.

Table 1 gives an overview of some early complementary feeding practices (24). In 1772, some experts noted that breast-feeding was likely to be adequate without other foods until 6–7 mo of age. Nevertheless, in the 1800s, complementary foods, especially cereals, were often introduced by 4 mo. In the 1950s, common practice had shifted to introducing complementary foods by ∼2 mo of age. In one survey of pediatricians in 1950, over two-thirds replied that the infants under their care were on complementary foods by 2 mo of age (24). This review of past practices highlights the wide variability in practices related to infant feeding over time.

TABLE 1

Historical complementary food practices (24)

TABLE 1

Historical complementary food practices (24)

Current recommendations for complementary feeding.

The American Academy of Pediatrics recommends initiation of complementary feeding to breast-fed infants between 4 and 6 mo of age (10) or at ∼6 mo of age (15,25). Although the American Academy of Pediatrics (10) notes that the order that foods are introduced is not generally of concern after 4 mo of age because of general maturity of the gastrointestinal tract, the typical order in which foods are introduced in the United States is iron-fortified infant cereal, then fruits and vegetables, and finally meats. Meats are often not introduced until at least 8 mo of age, and more commonly after 10 mo.

WHO recommends exclusive breast-feeding for the first 6 mo of life, that complementary foods be introduced at 6 mo of age, and that breast-feeding be continued (26). WHO and the Pan American Health Organization (18) have also made recommendations for the safe preparation and storage of complementary foods, food texture consistency, nutrient content, and meal frequency. They also promote appropriate and attentive interaction with infants. The texture consistency of complementary food should be developmentally appropriate so the infant can safely and adequately consume it as well as sufficient in terms of caloric content (e.g., thick vs. thin gruel). Good hygiene and proper food handling are important for prevention of disease, particularly diarrheal disease, which can be transmitted by pathogens.

WHO (27) and the Pan American Health Organization (18) further emphasize the importance of ensuring that nutrient needs be met by food variety, stating that “Meat, poultry, fish or eggs should be eaten daily or as often as possible.” Secondarily, “Vegetarian diets cannot meet nutrient needs at this age unless nutrient supplements or fortified products are used.” WHO recognizes that plant-based diets, especially those with limited variety, often lack sufficient essential minerals. Moreover, typical complementary food practices worldwide tend to provide poor sources of vitamin A, so vitamin A-rich fruits and vegetables are encouraged, and such foods will supply other essential nutrients as well.

Whether complementary foods will meet the nutrient needs of the infant will depend on the types of food selected. In Figure 2, which was adapted from WHO (27), the target goal for daily intake of key nutrients for a 12- to 23-mo-old infant is projected along with the percentage provided by breast milk and 1 meal of various foods. Breast milk alone nearly meets the target goal for vitamin A (assuming maternal vitamin A status is adequate) but not for energy, protein, or iron. If rice and beans are added to the meal, protein needs can be met. The further addition of green leafy vegetables and fish will meet the target goal for vitamin A (from the vegetables) but does not meet iron needs. If liver is substituted for the fish, iron (and vitamin A and zinc) needs are met, but the liver contributes modestly to the energy intake from the meal.

Figure 2

Percentage of daily goal intake that can be met by breast milk plus 1 meal of various complementary foods, comparing a meal with fish (A) and a meal with liver (B) for a 12- to 23-mo-old breast-fed infant. Adapted from WHO (27).

For zinc provision, there are differences across plant-based complementary foods vs. animal-based foods. Maize, wheat, rice, and roots are relatively low in zinc, as well as having the added complication of a high phytate-to-zinc molar ratio, making the zinc less bioavailable. For maize and wheat, a typical phytate-to-zinc molar ratio is ∼27, and for rice and roots typical ratios are somewhat lower, e.g., 14 and 10, respectively (19). There is no threshold phytate:zinc ratio below which there is no effect on bioavailability, but clearly ratios >20 would be expected to have a very substantial adverse effect on zinc absorption. Animal products have no phytate and have greater zinc concentrations than plant foods, except for dairy products, which have relatively low zinc (and iron) content. Red meat and liver are particularly rich food sources of zinc and iron.

Thus, current recommendations underscore the health benefit to the child of initiating meats with other complementary foods. They fall short, however, in emphasis on timing, i.e., that meats be introduced sooner than is commonly practiced.

Intake of complementary food in the United States.

In the Feeding Infants and Toddlers Study, Fox et al. (28) conducted a telephone survey of >3000 mothers or primary caregivers of infants between 4 and 24 mo of age in the United States. Only 20–26% of 7- to 11-mo-old infants were breast-fed on the day of the survey. Based on data from a 24-h recall, they calculated the percentage of 7- to 8-mo-old infants eating infant cereal (81%), vegetables (67%), fruit (76%), beef (3%), and yogurt/cheese (6%) at least once per day. These percentages of intake were similar to 9- to 11-mo-old infants for vegetables (73%) and fruit (76%). Intake of fruit juice was not included in this analysis. A lower percentage of the older infants consumed infant cereal (64%) daily, but a higher percentage consumed beef (8%) and yogurt/cheese (34%) than did the 7- to 8-mo-old infants.

For infants aged 7–11 mo, complementary foods providing their major sources of protein intake included mixed dishes, such as rice and turkey and pasta and turkey. These are more commonly fed than are plain meats. The baby food mixtures are much lower in iron and zinc than plain meats. Of the plain meats, poultry is more commonly consumed than beef or pork, but poultry is not as rich in iron and zinc as those meats. Results from the study in Denver described above (22,23), in which exclusively breast-fed infants were offered pureed beef as their first complementary food, demonstrated that meats are generally well accepted by 6- to 7-mo-old infants, and no difference was found in acceptability between cereal and meat.

Plant-based complementary food patterns, which are commonly consumed in the United States and in developing countries, are also very low in fat. So, in general, 6- to 12-mo-old breast-fed infants who are relying on the same feeding pattern reported by Fox et al. (28) have strikingly low fat intakes from complementary foods.

Strategies for complementary feeding

U.S. federal recommendations for meat as a complementary food.

At the national level, federal regulatory bodies have recommended strategies to address the micronutrient needs of breast-fed infants for more than a decade. The IOM (29) recommended meat, as well as iron-fortified cereal, as a complementary food for meeting the iron needs of 4-mo-old infants. The Centers for Disease Control and Prevention (30) reiterated the recommendation that meat could be used for 4- to 6-mo-old infants to meet their iron needs. However, these recommendations have not been widely acted on, despite concurrence from professional organizations such as the American Academy of Pediatrics (10). Most recently the IOM (31) Food and Nutrition Committee to Review the WIC Food Packages proposed to the USDA that meat should be provided as part of the food package for breast-fed infants at 6 mo of age.

On a global basis, complementary foods including meats have been recognized as a major component of child health and prevention of morbidity and mortality. This message has not been communicated and implemented as effectively as that for exclusive breast-feeding. Although considerable progress has been made in promoting exclusive breast-feeding, the success of strategies to promote appropriate timing and choice of complementary foods has been more limited. In part this is because complementary feeding presents enormous complexity in terms of different cultural norms, availability, and safe preparation. A number of health professionals have called for specific efforts to promote and support optimal complementary feeding strategies (32,33).

Research needs.

Several remaining questions about complementary feeding deserve further research. Efficacy and effectiveness studies are needed to evaluate the potential impact of optimizing complementary food choices on functional outcomes for the older infant and toddler. Additionally, it is not known whether complementary foods alone will meet micronutrient needs of children in regions where infants are frequently ill and may have recurrent episodes of infectious illness and associated increased nutrient losses, e.g., zinc losses with diarrheal illness. More information is also needed about the impact of complementary food choices on both micronutrient and macronutrient balance and metabolism. Qualitative research is needed to examine interventions that can achieve positive behavioral change related to infant complementary feeding practices and to examine sustainability.

In summary, various clinical factors affect the nutrient needs of infants during the first 6 mo of life, and infants differ individually somewhat in their requirements and in response to the environment. Zinc and iron, and in some circumstances vitamins A and B-6, are micronutrients identified as particularly problematic beginning at ∼6 mo of life, when human milk alone is inadequate to meet infant requirements. Infants do not necessarily become deficient at 6 mo, but the longer the infant receives an inadequate diet, the higher the risk is for nutrient depletion and adverse functional outcomes. Meats and liver provide a nutrient profile meeting the iron and zinc needs of the older breast-fed infant that is not easily provided by plant-based diets in the absence of food fortification or nutrient supplements. The feasibility of earlier introduction of meats, along with other complementary foods, merits systematic investigation to evaluate functional outcomes during the critical transition from exclusive breast-feeding to a full mixed diet.

Question and answer session

[Q1]: We do a lot of promotion of feeding, specifically liver, to children from 6 to 12 mo of age because it's relatively cheap, it's easy to mash, and it is nutritious. However, health professionals and pediatricians have raised concerns about potential toxicity from liver because of hormones, toxic substances, or other substances in liver. Do you have any information about the safety of feeding liver to infants?

[Dr. Krebs]: I am aware of the concerns over potential adverse consequences; it may be more than a theoretical concern. Because liver is rich in micronutrients, it does have many nutritional benefits for the infant. But without more safety data, we do not promote liver on a daily basis. There was an abstract at Experimental Biology this year that analyzed liver from Peru for some substances, perhaps pesticide levels, and actually found the results reassuring. But, at any rate, infants need to consume only a very small amount to meet their micronutrient requirements, and it does not have to be consumed every day. Other meat sources are rich sources of micronutrients as well. For beef, the infants in our Denver study were meeting their intake goals with only 2 oz a day, which is 1 jar of commercially available pureed beef.

[Q2]: I am a great proponent of meat intake for iron biology reasons, but we were involved in a successful rice biofortification, high-iron, and high-zinc feeding trial in the Philippines. By traditional breeding practices for crops, we were able to create a high-iron variety of rice and were able to show an improvement in iron status in reproductive-age women. Do you think this biofortification approach might have potential to add sufficient iron and zinc into complementary feeding strategies in places like Bangladesh, for example, where rice intake even in 6- to 9-mo-old infants can start to be quite substantial?

[Dr. Krebs]: There are many initiatives for fortification or biofortification of foods and staples, and yes, those are options. We've had some experience with phytate reduction of crops in Guatemala, and it is not a simple solution. There are, of course, availability and sustainability issues, whether those crops will grow in the local settings, etc. If one takes a whole-foods approach, the animal-source foods do offer a benefit, but there's room for plant-based alternatives, and we need research on such alternatives.

[Q3]: I was struck, in your 7-mo data, showing the gap between intakes and estimates of requirement, particularly when coupled with some of the morbidity data that you reviewed today. We have kind of an anomalous situation in the first year of life, and particularly in the first 6 mo of life, with the way we set the current Dietary Reference Intakes for infant feeding, looking at it from the nutritional perspective. Do you see ways that we can or need to add additional means, whether it is biochemical, functional, or outcome, in terms of getting better estimates of requirements, particularly for trace elements in this vulnerable population in the first 6 mo of life?

[Dr. Krebs]: Right. For example, with zinc, we're constantly struggling with the lack of an accurate index of zinc deficiency. In the case of iron, more reliable measures are available to document responses. Growth rates give a sense of the overall nutritional adequacy, but I also think it's probably not good to have zinc deficiency. But how do we demonstrate a deficiency? I've shown evidence to suggest there might be a problem with stunting and morbidity, but this is a nonspecific outcome. We need zinc-specific functional indices, but it is challenging. There is interest in some neurological testing beyond the Bayley Scales of Infant Development that are related to where zinc functions in the developing brain. Some other biochemical markers that reflect anabolic processes may be useful. There may be methodological explanations for why we have not seen effects of zinc supplementation in breast-fed infants in U.S. trials. We have not verified that there is actually a problem with zinc deficiency in U.S. infants, and yet you see these big gaps between intake and estimated requirements. The nutrition-related infectious morbidity is primarily apparent in developing countries.

[Q4]: Everything we feed before 6 mo of age is tamper-proof: human breast milk is absolutely tamper-proof, and by consensus, most of the formulas are tamper-proof as well. After 6 mo, as you say, anything might be fed, and only the child's rejection or the cultural rejection would be constraints on what is fed. So with complementary feeding, the infant is vulnerable to food-borne pathogens. In your graphs of ingested vs. absorbed zinc, were you depicting the Recommended Dietary Allowance (RDA) or the EAR—a median or mean? Because if it's the latter, I would like to see some more variance around your saturation curve and your projections to the axis.

[Dr. Krebs]: I was showing the average estimated physiologic requirement for absorption of 0.8 mg/d for a 7-mo-old infant and the EAR of 2.5 mg/d for intakes.

[Q5]: So there is a variance to that.

[Dr. Krebs]: Sure. And my only point was to illustrate that there's nothing magical about breast-fed infants; the more zinc you feed, the more absolute amount they will take up. If you feed only human milk, they may have efficient absorption, but it is only a percentage of what is available; they can't absorb more than what is there. They demonstrate absorption patterns consistent with saturation kinetics as adults do.

[Q6]: My question has to do with the absorption of zinc from cereals. You showed a slide of your U.S. data in Denver, and it appeared that infants were not absorbing that much (I assume that was a fortified cereal). Please comment on the bioavailability of the fortificant that is being used. In the international nutrition meeting symposium yesterday, I showed data from Ecuador, and Ken Brown showed similar data from Peru. Both of us found that a “pap” fortified with zinc sulfate had no significant impact in our program vs. control infants. And according to serum zinc, these infants were zinc-deficient. So might the problem be our measurement of zinc deficiency, or is it a problem with the zinc compound that is being used, or is the food matrix impacting zinc bioavailability?

[Dr. Krebs]: You have identified a number of complexities. The absorption data that we reported from Denver on iron-fortified cereal were obtained before Gerber had started fortifying infant cereal with zinc, and that was the brand we used. Now, other infant cereals are fortified with zinc, although not all of them—there are many “natural”-type products that are out on the U.S. market that are not fortified—but no bioavailability studies have been done on any of these products. There are mixed data on the bioavailability of the different forms of zinc supplements, but overall, there appears to be no substantial difference in the bioavailability of the oxide or sulfate forms. In our studies, there was a slightly lower fractional absorption of zinc from the rice cereal vs. the beef, but not as great a differential as we expected. Because there was relatively little zinc in the cereal, the absolute amount of zinc absorbed was very modest. But in zinc-fortified cereal I would predict that, even though the percentage fractional absorption may be relatively low, the absolute amount absorbed into the system would be more because the total amount consumed is more. And I'm surprised you didn't find differences in the plasma zinc levels.

[Q7]: Just a clarification, in the study that Ken Brown presented, there were 3 mg of zinc from the complementary food and a similar amount of zinc from the water-based supplement, and that didn't have any effect, either. So, if it was in fact a problem with bioavailability or matrix or something else, you would have expected to see a difference between the supplement and the complementary food, and we did not.

[Dr. Krebs]: Yes. Absorption from zinc sulfate is relatively high. I do not know how to explain your findings.

[Q6]: I am interested in the U.S. data that you showed on the breast-fed infants and the absence of the ability of the complementary foods to make up the difference. My understanding is that there is a common practice in the United States for breast-feeding mothers to also use some formula, and I didn't see any address of the potential the additional formula might have had in that total zinc status.

[Dr. Krebs]: In the bar graph you refer to (oral presentation), there was no formula contribution to zinc intake because of the inclusion criteria; those were exclusively breast-feeding infants in Denver. However, on a U.S. population basis, yes, formula feeding is very commonly used, and if it's acceptable to meet micronutrient needs by formula supplementation, then many in the population are doing it that way. But if we want to look at how we meet needs by encouraging extended breast-feeding, then that is where the gap is. I think 1 of the reasons that complementary feeding has not caught much attention or concern in the United States is that it is a minority of infants that are breast-fed past 6 mo. But if we successfully promote current recommendations, which are to breast-feed at least through 1 y, my opinion is that we ought to know how to support those infants so we are not setting them up for micronutrient deficiencies.

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Abbreviations

 

• EAR

  estimated average requirement

 

• IOM

 

• SGA

  small-for-gestational-age

 

• WIC

  Special Supplemental Nutrition Program for Women, Infants, and Children

Author notes

1

Published as a supplement to The Journal of Nutrition. Presented at the conference “Advances in Meeting the Nutritional Needs of Infants Worldwide,” held in San Francisco, CA, April 5, 2006. The conference was sponsored by the International Formula Council (IFC), Atlanta, GA. The contents are the sole responsibility of the authors. The papers comprising this supplement were developed independently, and the conclusions drawn do not represent the official views of IFC. The mention of trade names, commercial products, or organizations does not imply endorsement by IFC. Guest Editor was Catherine Klein, Life Sciences Research Office, Bethesda, MD. Guest Editor disclosure: C. J. Klein is an employee of the Life Sciences Research Office, which is under contract to the IFC to assist authors in preparing manuscripts for publication. Hence, the receipt of compensation from the supplement sponsor for services performed as guest editor is considered a potential conflict of interest. There are no other or pending financial interests with the sponsor, members of the sponsor's trade organization, or their products.

© 2007 American Society for Nutrition

© 2007 American Society for Nutrition

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