Abstract
Objective. To assess dietary nutritional quality during dietary transition to a modified adult-style diet in the second year of life.
Design. A total of 55 children from 12 to 18 months old and their parents were studied. Dietary intake and indices of growth were measured monthly. Dietary data were collected monthly and tabulated using the Minnesota Nutrient Data System. Data were evaluated using repeated-measures analysis of variance, time trend, and correlational analyses.
Results. Mean energy intake increased from 12 to 18 months of age (926 ± 24 kcal to 1062 ± 33 kcal) with contributions from energy-yielding macronutrients remaining relatively constant. Throughout the study, fat intakes were below 30% of energy for 22% to 33% of the sample. Micronutrient intake patterns were diverse with intake for some nutrients (vitamins A, C, B6, B12, and D and calcium) remaining above recommended levels despite changes over the course of the study. Folate intakes increased from 79% of the recommended value at 12 months old to ∼100% at 18 months old. Zinc and vitamin E intakes were well below recommended levels throughout the study, and iron decreased markedly from 96% of the recommended level at 12 months old to 76% at 18 months old.
Applications/Conclusions. These data show that intakes of some key nutrients are low during the period of dietary transition in early childhood, and intakes for some nutrients actually decrease despite increases in energy intake. Furthermore, because a considerable portion of children studied were consuming low-fat diets, it is clear that many parents are not following the only pediatric nutrition recommendations that currently exist. These findings argue strongly for the development of dietary guidance that not only addresses fat restriction, but also assists parents in selecting diets that support optimum growth and development in young children. nutrient intake, infants, dietary density.
- PUFA =
- polyunsaturated fatty acid
Recent national data highlight several nutritional problems in early childhood. Iron deficiency anemia is still relatively common (ie, 9%) in 1- to 2-year-olds in the United States,1despite Healthy People 2000 objectives to reduce iron deficiency to <3%.2 There is an increasing prevalence of overweight among preschoolers.3 At the same time, many young children consume diets, which, at lower than recommended fat levels,4 ,5 may compromise micronutrient intakes.6–9 Although there may be increased awareness about the nutritional needs of young children, there is a scarcity of representative data about children's nutritional patterns during the time of rapid dietary transitions in the second year of life.
Nutrient needs are high in the first year of life, and dietary recommendations are well-delineated.10 The second year of life is a time of steady growth and development during which nutrient needs remain high,11 but no official dietary guidance is directed to this age group except for the recommendation against restriction of fat.4 ,5 In fact, the Dietary Guidelines Advisory Committee that was responsible for setting the 1995Dietary Guidelines for Americans 12 suggested that further consideration should be given to separate guidelines for children below the age of 2 years. Dietary patterns in the second year change more rapidly than at any other time in life, while children continue to make the transition from predominantly milk/formula-based diets to adult-style diets. The nutrient needs for growth and maintenance13–15 necessitate transition to a nutrient-dense diet, because the percentage of kilocalories from milk and formula declines rapidly.16
In this study, we assessed the nutritional quality of children's diets in the second year of life, when infant foods are being replaced by adult-style food. We report that several key nutrients are low and diminish even further during dietary transition in early childhood. These findings demonstrate a need for nutritional guidance targeted to this age group.
METHODS
A total of 55 children from the State College, Pennsylvania area, a university-centered community, participated in this 6-month longitudinal study of growth and infant nutrition. Sample size was chosen based on a power calculation indicating that 50 children would permit adequate power (90%) to detect differences in measures of length. Sixty children were originally enrolled but 5 were dropped over the course of the study when caregivers failed to provide dietary records. Infants were identified through newspaper birth announcements. A mailing explaining the intent of the research was sent to their families. Telephone contact was made after the mailing. Parents expressing a willingness to participate in the study enrolled their children if they met the following criteria: 1) birth weight >2500 g, 2) no congenital abnormalities or perinatal complications, 3) no jaundice treated with phototherapy, 4) no hospitalization or supplementation with micronutrients during the 6 months before initiation of the study, 5) no chronic illness, and 6) birth weight, length, and head circumference within the 10th and 90th percentiles of the anthropometric reference values of the National Center for Health Statistics.17 Initial interviews were conducted between 11 and 12 months of age at which time informed written consent was obtained from the primary caregiver (most often the mother). Information on occupation of the primary wage earner and maternal education was also collected at this time for assessment of socioeconomic ranking.18 The use of human subjects was annually reviewed and approved by the Institutional Review Board of Pennsylvania State University.
Dietary Assessment
Three-day dietary records were collected at monthly intervals throughout the study. For the majority of subjects, mothers recorded all infant intakes, while for some, a secondary in-home caregiver recorded a portion of the dietary record. For those children who were in day care centers, we observed and recorded the intakes. Extensive instruction on how to describe and quantify the diet accurately was provided before dietary collection. Participants were instructed to use the 2-D Food Portion Visual (Nutritional Consulting Enterprises, Framingam, MA) to aid in portion size estimations. During the training period, we observed 2 meals served to the child and guided the recording of information.
All dietary records were complete at 12 and 18 months of age; 3 records were missing at 14 and 17 months of age; and 4 records were missing at 15 and 16 months of age. Dietary data were analyzed using the Diet Assessment Center at Pennsylvania State University, Department of Nutrition. Nutrient intakes were tabulated as 3-day averages using the Minnesota Nutrient Data System Software (Food Database 8A, Nutrient Database 28) developed by the Nutrition Coordinating Center (University of Minnesota, Minneapolis, MN). This database contains over 16 000 foods and over 4000 brand names. Summary data were transferred to Microsoft Excel (Microsoft Excel, Version 5.0, Microsoft, Cambridge, MA). Nutrient intake data were calculated as average amount per day (intake) and amount per 1000 kcal (nutrient density). Intakes were evaluated using currently available dietary standards.13–15
Anthropometric Measures of Growth
Anthropometric measures of growth (body weight, recumbent length, arm circumference, triceps, and subscapular skinfolds) were obtained monthly during home visits or in the day care center. Standard published procedures11 ,19 were used. The intraindividual and interindividual differences of measurement were less than ±10%.
Statistical Analyses
Repeated-measures analysis of variance statistics were applied to dietary data to assess possible effects of gender, time, and gender by time interactions. Trend analyses also were performed to describe changes over time. Three possible patterns were assessed: linear, quadratic, and cubic. A linear trend indicates that the change is unidirectional among consecutive time points; a quadratic trend is characterized by a curvilinear pattern, with just 1 shift in the direction over time; and a cubic trend indicates 2 changes in pattern direction over time. Correlational analyses were applied to associations among energy and nutrient intakes. All statistical analyses were performed using the Statistical Analysis System (SAS Institute, Inc, Cary, NC).
RESULTS
Demographic Characteristics
Mothers of children in this study averaged 33 years of age (21–46) and 16 years (10–22) of education. Children were born to families from middle to higher ranked socioeconomic households. The sample was 89% white, non-Hispanic with a racial/ethnic composition that resembled the population of the State College area,20which is less ethnically diverse than the nation as a whole.21 The average birth order among children studied was 2 (1–5).
Growth Indices
Anthropometric measures (weight, length, and arm circumferences) indicated that children were achieving growth that was assessed to be within normal ranges. Mean measures (± standard error of the mean) at 12 and 18 months old were 9.8 ± .1 kg and 11.1 ± .1 kg for weight (P < .0001), 75.4 ± .4 cm and 81.6 ± .4 cm for length (P < .0001), and 15.7 ± .2 cm and 16.2 ± .1 cm for midarm circumferences (P< .001), respectively. Triceps (7.7 ± .3 mm at 12 months old vs 7.1 ± .2 mm at 18 months old) and subscapular (5.8 ± .2 mm at 12 months old vs 5.6 ± .2 mm at 18 months old) skinfold measures did not change significantly over time. The majority of children (90%) remained within the 5th and 95th percentiles of reference distributions for weight and length17 as well arm circumference22 at both 12 and 18 months old. Using anthropometric reference values for skinfold measures,22most children were characterized as lean. Throughout the study, no >10% of children were above the 50th percentile for triceps skinfold measures and no >30% were above the 50th percentile for subscapular skinfold measures.
Dietary Assessments
Energy intake increased significantly from 12 to 16 months old and then seemed to level off through 18 months old (Fig 1). Corresponding intakes of the energy-yielding nutrients (carbohydrate, fat, and protein) also increased over time, while dietary density and percentage kilocalories derived from these classes of macronutrients remained relatively stable (Table 1). The increase in dietary density for sucrose approached significance (P = .06), and a large portion of children were consuming diets providing less than recommended levels of fat. At 12 and 18 months old, 12 (22%) and18 (33%) children, respectively, had fat intakes that furnished <30% of the kilocalories. For these children, mean percent of kilocalories derived from fat was 25.5 (17.6–29.5) at 12 months old, and 26.5 (15.9–29.9) at 18 months old. Although anthropometric measures were not related to the percentage of kilocalories from fat, length was found to be positively correlated to total fat intake in grams (P < .04) at 18 months old. Length was also positively related to energy (P < .03) at 18 months old, but not to protein or carbohydrate.
Mean (± standard error) energy intakes by children from 12 to 18 months old (n = 55).
Mean (± Standard Error) Energy and Macronutrient Intake, Dietary Nutrient Density, and Percent Kilocalories From Major Classes of Energy-Yielding Nutrients by Young Children Ages 12 to 18 Months*
Patterns for micronutrient intakes and densities did not always follow energy intake. In fact, intakes of 3 key nutrients (vitamins A and E and iron) significantly decreased over time, as did corresponding dietary densities (Table 2; Fig 2). Although vitamin A intake decreased over time, mean values remained above the recommended intake. Decreases in iron and vitamin E resulted in values well below reference standards: mean iron intake decreased from 9.6 to 7.6 mg/day (from 96% to 76% of the recommended intake) and vitamin E intake declined from 4.1 to 3.4 mg tocopherol equivalents/day (from 69% to 50% of the recommended intake). Children meeting recommended intakes at 12 and 18 months old represented 40% and 20% of the sample for iron and 24% and 9% of the sample for vitamin E, respectively. However, no child consuming <30% of kilocalories from fat met vitamin E recommendations at 12 months old and only one did so at 18 months old. Dairy furnished an average of 17% of vitamin E and 51% of iron at 12 months, but this contribution diminished dramatically over the study, coinciding with a decline in consumption of formula and human milk. At 12 and 18 months old, grains furnished an average of 14% and 33% of vitamin E and 68% and 76% of iron. Cereals alone contributed 26% of iron consumed at 18 months old. The mean contribution of meats to iron intakes was 8% and 14% at 12 and 18 months old, respectively. Although mean vitamin E intake decreased over the study, average polyunsaturated fatty acid (PUFA) intakes remained stable, resulting in a diminished vitamin E to PUFA ratio (.93 vs 3.71 mg of vitamin E per gram of PUFA;P < .0001). Vitamin E intake correlated positively with the percentage of kilocalories from fat at 12 months old (P < .002) but not at 18 months old.
Mean (± Standard Error) Intake and Dietary Nutrient Density for Selected Vitamins and Minerals by Young Children Ages 12 to 18 Months
Mean intake of selected micronutrients expressed as percentage of dietary reference standards13–15 for children from 12 to 18 months old (n = 55).
Although mean zinc intakes increased significantly over time from 4.8 to 5.3 mg/day, they remained at approximately one half of the recommended 10 mg/day at both 12 and 18 months old. The dairy and meat groups consistently contributed >50% and 25%, respectively, to zinc intakes throughout the study. Average folate intake increased from 60% to 100% of the recommended intake. Average vitamin D intake remained near the recommended level, while vitamins B6, B12, and C and calcium remained at levels greater than recommended intakes and did not increase significantly with energy intake (Fig 2; Table 2). Average dietary sodium intake increased by ∼50% during the period of transition (Table 2).
DISCUSSION
In this study, an incremental increase in energy intake was associated with normal growth of young children 12 to 18 months old. Although this period of growth is characterized by decreasing subcutaneous fat,11 using age-specific reference distributions,22 the children studied would be classified as lean. Mean energy intake associated with these patterns of growth was ∼1100 kcal/day at 18 months old. Although the current recommendation for children 1 to 3 years of age is 1300 kcal/day,13 there is a growing body of evidence that energy requirement for this age group is closer to 1100 kcal/day, as measured by studies of energy expenditure.23 The percentage of kilocalories furnished by protein, fat, and carbohydrate was 15, 33, and 54, respectively, and is nearly identical to that reported in a recent nationwide survey for this age group.24
Although dietary recommendations are not well-delineated for the second year of life, there is a strong nutrition message not to restrict dietary fat until after 2 years old, and then to do so gradually, so that by 5 years old energy furnished by fat is <30% of kilocalories.4 ,5 Nonetheless, in our study, we found that 22% of children at 12 months old and 33% at 18 months old were consuming diets providing <30% of energy from fat. This finding raises concerns in light of the positive relationship observed between fat intake and length, an important indicator of growth. Although we did not assess whether there was a conscious effort to restrict fat by caregivers, these findings mirror recent national survey data for this age group, suggesting that feeding low-fat diets to children in the second year of life is a widespread practice in the United States. Thus, even when dietary recommendations are evident, adherence is primarily lacking. The lack of adherence may only reflect the inability of caregivers to translate broad nutrition objectives into food selection patterns for this age group. Therefore, practitioners need to stress that fat reduction strategies that are appropriate for adults, such as use of nonfat and reduced-fat dairy products, are to be avoided for this age group. The use of whole milk rather than fat-modified milks should be encouraged.
Patterns of micronutrient intake were quite diverse. Intakes for some nutrients remained well above recommended levels regardless of whether they changed over the study. In sharp contrast were the nutrients, zinc, and vitamin E, with intakes remaining below recommended amounts throughout the study and iron, with intakes declining to well below recommended amounts by 18 months old. These 3 nutrients were also cited in the Third Report on Nutrition Monitoring in the United States 25 as current or potential public health issues for children 1 to 2 years of age.
The decline in iron intake is particularly noteworthy because it is a current public health issue25 based on low intakes as well as biochemical and clinical outcomes. The current estimate for prevalence of iron deficiency among 18-month-old children in the United States is ∼9%.1 The essentiality of iron for growth and motor and mental development has been established.26 ,27Recent data on mental development in children participating in the Special Supplemental Program for Women, Infants, and Children found an association between early iron deficiency and mild or moderate cognitive deficits of school-aged children.28 This study also supports other findings27 ,29 ,30 that consequences of early iron deficiency may not be completely reversible.
Zinc and vitamin E are classified as nutrients that pose potential public health issues and require further study.25 This classification is assigned to nutrients based on low dietary intakes but limited biochemical, clinical, or anthropometric evidence of adverse health outcomes. Assessment of both zinc and vitamin E has been difficult because of a lack of sensitive biomarkers of nutritional status. Nonetheless, these nutrients are important for growth and health of children. Zinc deficiency decreases immunocompetence,31 which may increase the risk of infectious diseases as well as diarrhea.32 Zinc deficiency may impair children's cognitive performance, as well as reduce growth velocity.33 The consequences of low vitamin E intakes in children are difficult to interpret. Vitamin E is also essential for the maintenance of the immune system34 and is a critical antioxidative vitamin.35 However, the impact of low dietary intakes of vitamin E on oxidative stress is complicated by interactions among other antioxidant nutrients. The abundance of other cellular antioxidants, such as vitamin C, selenium, and carotenoids, may have a sparing effect on vitamin E status.36
Both nationwide survey data and longitudinal studies such as ours37 have indicated that nutritional quality may be compromised during the second year of life. Yet there are almost no pediatric guidelines for this critical period of progression from a diet composed nearly exclusively of infant foods to one composed of nearly solely adult foods.38 Present findings argue strongly for the development of anticipatory guidance to ensure adequate intakes of all nutrients throughout the period of dietary transition.
Nutritional guidelines for the second year of life must focus on foods that are commonly consumed and that provide the nutrients at risk of being low for children of this age group. In our study, the grains, dairy, and meat groups were identified as important sources of problem nutrients: iron, zinc, and vitamin E. As iron-fortified formulas (.03–.4 mg of iron per fluid ounce)39 and infant cereals (3.5 mg per once prepared)39 were gradually phased out of the diet in the second year of life, a decline in iron intakes was observed. This finding suggests that a conscious effort must be made by caregivers to select and offer foods high in iron, so young children's intakes will be maintained during dietary transition. Because cereals contributed substantially to intakes of iron as well as vitamin E and zinc in our study, we recommend the use of fortified ready-to-eat cereals or cooked cereals as excellent sources of these nutrients. Because not all cereals are equally fortified, caregivers should be advised to refer to nutrition labels to select cereals that are high in iron, zinc, and vitamin E. The meat group contributed significantly to intakes of iron and zinc and, as a highly bioavailable source, could be emphasized to enhance intakes of these nutrients. Additionally, pediatric guidance should continue to emphasize the dairy group; it was the primary food group contributor to intakes of zinc among children studied and is a rich source of many other important nutrients as well.40
ACKNOWLEDGMENTS
This research was supported in part by the National Dairy Council.
We thank the parents and children who participated in the study, and Kate Wagner for her assistance in the coordination of field activities.
Footnotes
- Received April 6, 1999.
- Accepted January 3, 2000.
Reprint requests to (M.F.P.) S-129C Henderson Bldg, Pennsylvania State University, University Park, PA 16802. E-mail:mfp4{at}psu.edu
REFERENCES
- Copyright © 2000 American Academy of Pediatrics
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