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Keywords:

  • environmental influences;
  • intake regulation

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Research Methods and Procedures
  5. Results
  6. Discussion
  7. Acknowledgments
  8. References

Objective: Whether developmental periods exist in which children become particularly sensitive to environmental influences on eating is unclear. This research evaluated the effects of age on intake of large and self-selected portions among children 2 to 9 years of age.

Research Methods and Procedures: Seventy-five non-Hispanic white children 2 to 3, 5 to 6, and 8 to 9 years of age were seen at a dinner meal in reference, large, and self-selected portion size conditions in which the size of an entrée was age-appropriate, doubled, and determined by the child, respectively. Weighed food intake data were collected. Entrée bite size and bite frequency were assessed. Height and weight measurements were obtained.

Results: The effect of age on children's intake of the large portion was not significant. Entrée consumption was 29% greater (p < 0.001) and meal energy intake was 13% greater (p < 0.01) in the large portion condition than in the reference condition. Increases in entrée consumption were attributable to increases in average bite size (p < 0.001). Neither child weight nor maternal weight predicted children's intake of large portions. Self-selection resulted in decreased entrée (p < 0.05) and meal energy (p < 0.01) only among those children who ate more when served the large portion.

Discussion: The results of this research confirm that serving large entrée portions promotes increased intake at meals among 2- to 9-year-old children. These findings suggest that any age-related differences in children's response to large portions are likely to be smaller than previously suspected.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Research Methods and Procedures
  5. Results
  6. Discussion
  7. Acknowledgments
  8. References

Eating environments that offer convenient access to large portions of palatable, energy-dense foods may be obesigenic (1, 2, 3). Young children show an ability to self-regulate meal and daily energy intake under laboratory conditions (4, 5, 6). At the same time, exposure to large food portions produces increases in children's energy intake at meals (7, 8). The age at which children become susceptible to portion size, however, is unclear. In the first published study of portion size in children, small, medium, and large portions of a lunch entrée were served to preschool-age children on three separate occasions (7). Four- to 6-year-old children showed increased entrée and meal energy intake across conditions of increasing entrée portion size. Intake among 2- to 3-year-old children, however, did not vary across conditions. In subsequent research, doubling an age-appropriate portion of macaroni and cheese resulted in increases in entrée consumption for both younger (3 to 4 years) and older (4 to 5 years) preschool-age children (8). Children also ate less when allowed to serve themselves than when served large portions, suggesting that encouraging self-serving might have a protective role against the intake-promoting effects of exposure to large portions. Understanding whether there are critical periods in which children become sensitive to factors in their environments that may promote increased intake is important for prevention efforts.

While the aforementioned studies tailored entrée serving size to children's age, neither was specifically designed to evaluate the effect of age on children's response to large portions; in each case, the difference in age between younger and older groups of preschool-age children was a year or less. This research was designed to systematically study the effects of age on children's responsiveness to large and self-selected portions. Given that ingestive behavior is modified by environmental factors from the earliest stages of development (9), the main hypothesis to be tested was that serving large portions would produce increases in food and energy intake in both younger and older children. Consistent with the findings of Fisher et al. (8), the author hypothesized that children's intake of self-selected portions would be less than when served a large portion.

A secondary aim of this study was to evaluate the basis of individual differences in children's intake of large portions. Whether overweight children are particularly susceptible to overeating large portions is unclear. In experimental research, preschool-age children's intake of large portions was positively associated with eating in the absence of hunger in a separate setting (8) but not with weight status (7, 8). Positive associations of weight with average food portion size and average meal portion size have been reported among toddlers and adolescents participating in the Continuing Survey of Food Intake by Individuals, 1994 to 1996 and 1998, but not among preschool-age children (10, 11). This study evaluated whether children's intake of large portions was associated with child or maternal weight status and maternal disinhibited eating.

Research Methods and Procedures

  1. Top of page
  2. Abstract
  3. Introduction
  4. Research Methods and Procedures
  5. Results
  6. Discussion
  7. Acknowledgments
  8. References

Participants

Participants were 75 children (44 boys and 31 girls) in three age groups: 2 to 3, 5 to 6, and 8 to 9 years of age. These age groupings were chosen to be more clearly delineated than those of the previous studies (7, 8), roughly corresponding to preschool, entry to school, and elementary school periods. In the interest of drawing parallels with the previous studies, the sample was restricted to non-Hispanic white children. Child exclusion criteria were the presence of any chronic medical condition or medication use affecting food intake, food allergies, BMI-for-age of <5th percentile, and dislike of two or more foods on the experimental menu. The convenience sample was recruited using flyers posted in the community and the USDA Children's Nutrition Center's website, publications, and volunteer databases. Participant characteristics are shown in Table 1. On average, children were of normal weight, as indicated by a mean BMI percentile of 71 ± 30%; however, 20 of 75 children were overweight. Mothers were in their mid-30s (mean age, 37 ± 6 years), overweight (mean BMI, 29 ± 7 kg/m2), and well educated (70/75 reported some college or further education). Mothers of younger children tended to be heavier (p < 0.01) and younger themselves (p < 0.0001). Roughly one half of the mothers reported being employed (38/75). Mothers provided written consent for their own participation and assent for their child's participation. All procedures were reviewed and approved by the Institutional Review Board at Baylor College of Medicine.

Table 1.  Sample characteristics
 2 to 3 years5 to 6 years8 to 9 yearsEffect of child age
  • Means with different superscripts are significantly different from one another.

  • Values are mean ± SD.

  • *

    Possible mean item scores range from 1 to 5, with higher scores indicating higher levels of the construct.

Child    
 Age (years)2.6 ± 0.5a5.6 ± 0.5b8.7 ± 0.4cp < 0.0001
 Sex17 boys, 8 girls17 boys, 8 girls10 boys, 15 girlsNS
 BMI percentile76 ± 33*61 ± 3175 ± 25NS
Mother    
 Age (years)33 ± 6a36 ± 5b40 ± 5cp < 0.0001
 Greater than high school education24/2523/2523/25NS
 Employment11/2510/2517/25NS
 BMI (kg/m2)33.2 ± 9.3a27.7 ± 5.5b27.3 ± 4.7bp < 0.01
 External disinhibition*3.0 ± 0.62.9 ± 0.43.0 ± 0.5NS

Design

A between-subjects design with a within-subjects component was used. Each child in each of the three age groups was seen in three conditions in which the size of a macaroni and cheese entrée was manipulated: a reference condition, a large condition in which the entrée portion was doubled, and a self-selected condition in which the entrée portion was doubled but provided in an individual serving dish. Fixed portions of other foods and beverages were also offered at each meal. Condition sequence was randomly assigned. The conditions were spaced 1 week apart. Weighed intake methods were used to assess children's intake. Children's bite frequency and bite size, as well as any comments about portion size, were measured using behavioral observations. Children's preferences for the entrée and for other foods were obtained. Height and weight measurements were obtained from each child and their mother. Mothers also provided self-report data on demographics and their own disinhibited eating.

Procedure

Children's intake at a dinner meal was measured on three separate occasions at the USDA Children's Nutrition Research Center's Children's Eating Laboratory, Houston, TX. Parents were instructed to refrain from giving their child any foods or beverages for 2 hours before the visit. On arrival, a research member interviewed the parent to confirm that those instructions had been followed. Preference data for the foods on the experimental menu and height and weight measurements were obtained on arrival at the first visit to the center. After those measurements, three to four children were served dinner together in the presence of a research staff member. To minimize visual comparisons of portion size, each child was assigned to eat with children of similar age in the same portion size condition. Children were instructed not to share food and to eat as little or as much as desired during the 20 minutes allotted for dinner. Mothers completed self-report questionnaires in an area separate from where their children ate.

Experimental Menu

The entrée food was a commercially available macaroni and cheese with an energy density of 1.42 kcal/g. Entrée portions in the reference condition were initially specified by reviewing those used in the previous studies (7, 8), in conjunction with amounts corresponding to the 50th to 75th percentile for macaroni and cheese consumption data at a single eating occasion from the Continuing Survey of Food Intakes of Individuals, 1994 to 1996 (12). Consistent with the previous studies, serving sizes differed by age; the reference serving portions were 200, 250, and 450 grams, respectively, for the 2 to 3, 5 to 6, and 8 to 9 year olds (Table 2). The reference condition entrée portions for the two youngest groups were between the 75 and 90th percentiles of intake among 2 to 5 year olds from the Continuing Survey of Food Intakes of Individuals, 1994 to 1996, data and were 75 grams higher than those used in the study of Fisher et al. (8) but were between the small and medium portions used in the experiment first describing age-related differences (7). Pilot testing revealed the need to make upward adjustments to the amount specified for 8- to 9-year-old children (initially 300 grams) to avoid artificially restricting intake in the reference condition. As a consequence, the reference portion for the 8- to 9-year-old children was above the 90th percentile for 6- to 11-year-old children participating in the Continuing Survey of Food Intakes of Individuals, 1994–1996 (12).

Table 2.  Experimental menu for reference condition
 2 to 3 years5 to 6 years8 to 9 years
Macaroni and cheese200 grams250 grams450 grams
2% milk1 carton; 240 grams1 carton; 240 grams1 carton; 240 grams
Corn82 grams84 grams85 grams
Applesauce1 container; 112 grams1 container; 112 grams1 container; 112 grams
Carrots39 grams39 grams39 grams
Chocolate chip cookies2; 22 grams3; 33 grams3; 33 grams
Total energy (kcal)8119331219

Serving sizes for other foods on the standard menu were generous and did not vary across conditions (Table 2). These foods were included to minimize the extent to which any portion-size related changes in entrée intake were attributable to limited food choice. These portions generally fell between the 50th and 75th percentiles of intake per eating occasion by children 2 to 5 and 6 to 11 years old participating in the Continuing Survey of Food Intakes of Individuals, 1994 to 1996 (12). In cases where survey data indicated no or little difference in intake at a given percentile between 2 and 5 and 6 and 11 year olds, the same portion size was assigned to the three age groups, often a customary unit (e.g., a carton of milk). For instance, the 75th percentile for raw carrot intake per eating occasion was 39 grams for both 2 to 5 and 6 to 11 year olds. Similarly, the 75th percentile for applesauce intake was 127 and 126 grams for 2 to 5 and 6 to 11 year olds, respectively; all age groups were offered a 4-oz (112 grams) pre-packaged portion. Fluid milk intake at the 75th percentile was 242 and 264 grams for 2 to 5 and 6 to 11 year olds, respectively; each age group was served a 240-gram carton. Total energy provided for the dinner meal in the reference condition was ample: 811, 933, and 1219 kcal, respectively, for the 2 to 3, 5 to 6, and 8 to 9 year olds.

Intake Measures

Intake of the Main Entrée and Other Foods

Children's consumption of the entrée and other foods at the meal was measured using weighed food intake data. Manufacturers’ data were used to convert consumption in grams to energy (kilocalories).

Children's Comments about Portion Size

Children's comments regarding entrée portion size were recorded in each condition by a research staff member.

Children's Bite Size and Frequency

The total number of bites of the entrée was recorded in each condition. Bite frequency was calculated as the sum of all bites of entrée during the 15-minute period. Average bite size was calculated for each child as the total grams of entrée consumed, divided by the total number of bites of the entrée taken (grams per bite).

Other Measures

Maternal and Child Weight Status

Trained nurses measured height to the nearest 0.1 cm and weight to the nearest 0.1 kg. Center for Disease Control and Prevention Growth Charts (2000) were used to calculate age- and sex-specific BMI z-scores for each child (13). Child overweight was defined as a BMI z-score >95th percentile. Maternal BMI was calculated as weight in kilograms divided by height in meters squared.

Maternal Disinhibition

The Dutch Eating Behavior Questionnaire, consisting of 33 items, was used to measure externally disinhibited eating among mothers (14, 15). The external disinhibition subscale measures overeating occurring in response to the sight and/or smell of palatable foods. This construct was included because of the focus of this study on situational influences on children's intake. Mean item scores using a five-point Likert scale were used to measure the construct, with higher scores indicating higher levels of externally disinhibited eating.

Food Preference

Children's preferences for foods on the experimental menu were obtained using a tasting assessment method developed by Birch (16, 17). Briefly, children were presented with two bites of each food and asked to taste the food and indicate their preference as being either “yummy,” “yucky,” or “just okay.” To assess familiarity, children were asked whether they had ever eaten each food. Data from 3 of 75 children were incomplete. All but 1 child reported previously eating the macaroni and cheese entrée, and 72 of 74 rated the entrée as either “yummy” or “just okay.” Children who rated the macaroni as “yummy” did not differ from those who rated the macaroni as either “just okay” or “yucky” in terms of sex (χ2 = 0.23, p = 0.63), age (χ2 = 1.60, p = 0.45), or overweight status (χ2 = 0.12, p = 0.73). Most of the children reported having previously eaten the other foods (carrots: 70 of 75; applesauce: 71 of 75; cookies: 72 of 74; corn: 73 of 75; 2% milk: 73 of 74) and rated the other menu foods as tasting either “yummy” or “just okay” (carrots: 61 of 72; applesauce: 68 of 74; cookies: 72 of 74; corn: 67 of 74; 2% milk: 73 of 75).

Statistical Analyses

Statistical analyses were performed using SAS Version 9.1 (Cary, NC). Descriptive statistics were generated for all variables of interest; mean ± SD is presented unless otherwise indicated. Because each age group was served and expected to consume different amounts of the entrée, relative change scores were used to evaluate individual differences in children's susceptibility to overeat large portions. Intake in the large portion condition was expressed relative to intake in the reference condition: (large portion intake – reference portion intake)/reference portion intake × 100. For instance, a score of 30 would indicate a 30% increase in entrée intake in the large portion size condition, relative to the reference condition. To evaluate whether allowing children to self-select portion size when exposed to large amounts of food is beneficial, intake in the self-selection condition was compared with intake in the large condition: (self-selected portion intake – large portion intake)/large portion intake × 100. In this case, a score of −30 would indicate a 30% decrease in entrée intake when allowed to self-select than when served the large portion. A dummy variable representing age grouping (2 to 3, 5 to 6, 8 to 9 years) was used to predict relative change scores using analysis of covariance; the main analyses controlled for child preference for the entrée, condition order, and child gender. Child BMI z-score, maternal BMI, and maternal disinhibition were evaluated as predictors in separate models. Mixed models were used to assess whether entrée intake was similar among groups of children who ate together. Statistical significance was indicated by p < 0.05.

Results

  1. Top of page
  2. Abstract
  3. Introduction
  4. Research Methods and Procedures
  5. Results
  6. Discussion
  7. Acknowledgments
  8. References

Complete intake data were obtained from 75 children. Because relative change in entrée consumption across conditions was of primary interest, cases in which entrée intake was 0 grams were not included in analyses: eight in the reference condition, two in the large portion condition, and four in the self-selection condition. Also excluded from data analyses were two cases in which change scores were >3 SD above the mean: one case comparing entrée intake in the reference and large portion conditions (339% increase) and one case comparing entrée intake in the large and self-selection conditions (226% increase). Analyses of relative change in entrée intake from the reference to large portion condition were performed on 65 cases. Those 10 excluded cases tended to be boys (χ2 = 4.7, p < 0.05) from the two youngest age groups (χ2 = 8.5, p < 0.01) but did not differ from those retained on the basis of child overweight (χ2 = 1.0, p = 0.31). Relative change from large to self-selected condition was performed on 69 cases. Those six excluded cases tended to be boys (χ2 = 4.6, p < 0.05) but did not differ from those retained on the basis of child age (χ2 = 4.3, p = 0.11) or overweight (χ2 = 0.1, p = 0.70).

Intake in the Reference Condition

The amount of food provided in the reference condition did not artificially restrict entrée or total energy intake. On average, children consumed 56 ± 27% of the reference entrée; the proportion consumed did not differ by age group (F = 2.8, p = 0.07), child BMI (F = 1.6, p = 0.21), condition order (F = 0.4, p = 0.70), or entrée preference (F = 3.3,p = 0.08) but was higher among boys than girls (61% vs. 42%; F = 8.5, p < 0.01). The number of children consuming 95% or more of the entrée in the reference condition was two, three, and two for the 2 to 3, 5 to 6, and 8 to 9 year olds, respectively. Similarly, total energy in the reference condition was not limiting; children consumed 47 ± 17% of total energy provided in the reference condition. The proportion of available energy consumed by children tended to be lowest among girls (39% vs. 49%; F = 6.5, p < 0.01) and the youngest group (30% vs. 49% and 53% in the 2 to 3, 5 to 6, and 8 to 9 year olds, respectively; F = 11.1, p < 0.0001) but did not vary by child BMI (F = 1.3, p = 0.26), condition order (F = 0.3, p = 0.74), or entrée preference (F = 2.2, p = 0.14).

Intake in the Large Condition

Analysis of individual change revealed that children's entrée consumption was, on average, 29% greater in the large portion condition than in the reference condition (F = 11.0, p < 0.001); 63% of the children showed increases in entrée intake from the reference to large portion condition. Group means for energy intake in each condition are shown in Table 3. Among 2- to 3-year-old children, mean intake of the large portion entrée (102 grams; ∼0.5 cup) fell between the 25th and 50th percentiles of macaroni and cheese intake per eating occasion for 2 to 5 year-old children participating in Continuing Survey of Food Intakes of Individuals, 1994 to 1996 (12). Intake of the large portion entrée among children 5 to 6 years old (204 grams; a little less than 1 cup) fell between the 50th and 75th percentiles for children 6 to 11 years old participating in Continuing Survey of Food Intakes of Individuals, 1994 to 1996, and intake among children 8 to 9 years old (286 grams; 1.25 cups) was slightly higher than the 75th percentile of consumption (12).

Table 3.  Group means for energy intake in the reference, large, and self-selected conditions
 2 to 3 years5 to 6 years8 to 9 years
 Reference (N = 18)Large (N = 18)Self (N = 21)Reference (N = 22)Large (N = 22)Self (N = 23)Reference (N = 25)Large (N = 25)Self (N = 25)
  1. Values are mean ± standard deviation kilocalories.

Entrée133 ± 82145 ± 113127 ± 92223 ± 83290 ± 145241 ± 156361 ± 173407 ± 258380 ± 270
Other foods143 ± 80149 ± 59153 ± 68257 ± 84271 ± 96260 ± 80276 ± 85294 ± 81261 ± 94
Total energy276 ± 135294 ± 123280 ± 134480 ± 128562 ± 179501 ± 179637 ± 190700 ± 282641 ± 286

Change in entrée consumption did not vary by age (F = 0.9, p = 0.40). As shown in Figure 1, the sample means ± SE for 2 to 3, 5 to 6, and 8 to 9 year olds were 29 ± 21%, 43 ± 14%, and 18 ± 13%, respectively; however, differences between these means were not statistically significant. The magnitude of change in entrée intake did not vary by condition order (F = 0.3, p = 0.74), preference for the entrée (yummy vs. just-okay/yucky; F = 0.1, p = 0.74), or eating >95% of the entrée in the reference condition (F = 0.8, p = 0.37) but was greater among girls than boys (47% vs. 11%; F = 3.9, p < 0.05). Similarly, child BMI (F = 1.0, p = 0.32), maternal BMI (F = 0.2, p = 0.64), and maternal disinhibited eating (F = 1.1, p = 0.29) were not associated with entrée change scores representing children's response to large portions. Table assignment at each visit did not predict entrée intake after controlling for age and condition assignment (data not shown).

image

Figure 1. Intake of entrée in large portion condition relative to reference condition. The sample mean is given by the horizontal line. Lower and upper edges of the box represent the 25th and 75th percentiles, respectively. Lower and upper boundaries of the whiskers indicate the 10th and 90th percentiles, respectively.

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Total energy intake was, on average, 13% higher in the large portion condition than in the reference condition (F = 8.2, p < 0.01), with 60% of children showing increases in total energy consumed at the meal. Among 2- to 3-year-old children, total meal energy in the large portion condition was less than mean meal energy for 3- to 5-year-old children participating in Continuing Survey of Food Intakes of Individuals, 1994 to 1996 and 1998 (sample mean = 294 kcal vs. Continuing Survey of Food Intakes of Individuals mean = 389 kcal) (11). However, mean energy consumption in the large portion condition among children 5 to 6 (562 kcal) and 8 to 9 years old (700 kcal) was greater than average meal energy for 6- to 11-year-old children participating in Continuing Survey of Food Intakes of Individuals (509 kcal) (11). The magnitude of change in energy intake at the meal from reference to large portion condition did not vary by child age group (F = 1.1, p = 0.33), condition order (F = 0.6, p = 0.57), preference for the entrée (F = 0.2, p = 0.69), eating >95% of the entrée in the reference condition (F = 1.3, p = 0.26), or sex (F = 0.6, p = 0.43). Similarly, changes were not associated with child BMI (F = 0.2, p = 0.66), maternal BMI (F = 0.0, p = 0.97), and maternal disinhibited eating (F = 0.6, p = 0.46).

Bite Frequency and Size

As reported in Fisher et al. (8), the increase in entrée consumption was attributable to an increase in bite size (9 ± 5 and 11 ± 6 g/bite in the reference and large portion conditions, respectively; F = 15.3, p < 0.001), with the majority (67%) of children showing increases in bite size. In contrast, less than one half (49%) of children showed increases in total bite frequency when served the large entrée portion; bite frequency did not differ across conditions (23 ± 14 bites in the reference condition vs. 21 ± 15 bites in the large condition; F = 0.2, p = 0.64). The sample was dichotomized to compare the bite parameters of children who ate more of the entrée when served the large portion than when served the reference portion to those children who did not eat more. As shown in Figure 2, children who ate more of the large portion entrée showed increases in both bite size (p < 0.01) and the total number of bites taken (p < 0.001). In contrast, children who ate the same amount or less of the large portion showed increases in bite size when served the large portion (p < 0.05) but decreases in the total number of bites taken (p < 0.001).

image

Figure 2. Changes in bite number and size for children who ate more of the entrée in the large portion condition than in the reference condition and for children who did not. Data are presented as mean ± standard error. ****Different from the value observed among children who ate more when served the large portion (p < 0.0001).

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Given the association of portion size and bite size observed within each age group, we further evaluated whether children's mean bite size was ordered across the range of entrée serving sizes used in this experiment (200, 250, 400, 450, 500, and 900 grams), without consideration of child age. Figure 3 depicts mean bite size data for each entrée serving size. Indeed, greater entrée serving portions were predictive of greater mean bite sizes (β= 0.006, SE = 0.001, p < 0.0001).

image

Figure 3. Mean bite size (standard error) across the range of entrée serving portions used.

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Comments about Entrée Portion Size

Children made few comments about portion size. Seven of 75 children made comments in the large portion condition (e.g., “This is a lot of mac and cheese”; “This is a lot of food”; “This is more food than we get to eat at home”), whereas only one child made similar comments in the reference portion condition. Of note, three children spontaneously indicated being full in the reference condition, whereas seven children indicated being full in the large portion condition.

Intake in the Self-selected Condition

Group means for energy intake in the self-selected condition are shown in Table 3. Analysis of individual change revealed that children's entrée consumption in the self-selected portion size condition was not different from that in the large portion condition (F = 0.7, p = 0.41). The sample was again dichotomized to compare self-selection of those children who ate more when served the large portion to those who did not. Allowing children to self-select entrée portion resulted in decreased entrée intake for 40 of the 65 children who ate more when served the large portion than when served the reference portion. Among those 40 children, self-selected entrée intake (means by age group = 102 grams among children 2 to 3 years old, 181 grams among children 5 to 6 years old, 315 grams among children 8 to 9 years old) was 17% less (p < 0.01), and total energy intake at the meal was 11% less (p < 0.01), than in the large portion condition. Among the group of children who ate the same amount or less of the entrée in the large condition than in the reference condition, self-selected entrée intake was actually 36% higher than in the large portion condition (p < 0.001) but did not differ from entrée intake in the reference condition (p = 0.13). Furthermore, self-selected intake of those children (means by age group = 80 grams among children 2 to 3 years old, 190 grams among children 5 to 6 years old, 195 grams among children 8 to 9 years old) was, in absolute terms, similar to or less than the self-selected intake of the rest of the sample.

Discussion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Research Methods and Procedures
  5. Results
  6. Discussion
  7. Acknowledgments
  8. References

Preschool-age children have shown an ability to self-regulate energy intake in controlled laboratory conditions (4, 5). These abilities, however, can be readily disrupted by social and situational conditions of the environment in which eating occurs (18, 19). For instance, limiting children's access to a preferred food has been shown to produce increases in its selection and consumption when the food becomes available (19). The results of this research provide new evidence that portion size promotes energy intake at meals in children as young as 2 years of age. In this study, entrée consumption among 2- to 9-year-old non-Hispanic white children was 29% greater when the children were served a large portion compared with an age-appropriate portion. These results were observed despite the fact that children consumed, on average, only 56% of the entrée in the reference condition and may not have been appreciably aware of changes to the entrée portion size. Serving the large portion entrée also resulted in a 13% increase in total energy consumed at the meal. The fact that most children did not fully consume the reference entrée portion or total available energy in the reference condition suggests that intake was excessive when the large entrée portion was served.

The findings that large portions produced increases in entrée and total meal energy among 2- to 9-year-old children are consistent with those of Fisher et al. (8) and a recent analysis of Continuing Survey of Food Intakes of Individuals data (20), showing relationships between average food portion size and daily energy intake in younger (2 to 3 years) and older preschool (4 to 6 years) children. In contrast to the results of Rolls et al. (7), entrée and total meal energy of 2- to 3-year-old children were significantly increased when large entrée portions were served. Furthermore, in this study, portion size–related increases in total meal energy did not vary by age. In other words, the 2 to 3 year olds did not differ from older children in the extent to which they compensated for intake of the large entrée by consuming less of other foods served at the meal. Therefore, the findings of this study do not support the idea of a significant developmental shift in children's susceptibility to portion size during early childhood.

Why age-related effects on children's intake of large portions differed across studies is not obvious. This study used the same type of entrée (macaroni and cheese) as in Rolls et al. (7) and similar large entrée portion sizes for the 2- to 3-year-old children [400 grams in this study vs. 376 grams in the study of Rolls et al. (7)]. By design, the youngest group of children was, on average, 3 years younger than children in the next age group, whereas the mean age difference between younger and older age groups in the previous studies was less than a year (7, 8). Presumably, this difference would have made any such age differences easier to detect rather than more difficult. Other methodological differences between studies include time of day [dinner meal in this study vs. a lunch meal in previous research (7, 8)], experimental setting [laboratory setting in which children ate with unfamiliar peers in this study vs. a daycare setting with familiar peers in the previous research (7, 8)], and the number of accompanying foods offered [this study offered corn and cookies in addition to those foods used by Rolls et al. (7)]. That the aforementioned factors would differentially affect the youngest age group's intake of the reference and large portion entrées, however, is unlikely in that the factors were held constant across conditions. In fact, the proportion of total energy consumed from accompanying foods in the youngest age group was similar across studies [51% to 62% in the study of Rolls et al. (7) vs. 51–52% in this study]. Although parents were instructed to withhold food and beverage for 2 hours before the session, it is possible that variability in child hunger could have also influenced energy intake at the meal. The fact that the order of condition presentation was varied among children, however, argues against a systematic bias that would account for the observed portion size effects. One potentially significant difference between studies is that this study expressed children's intake of the large entrée portion relative to entrée intake in the reference condition to take into account the fact that the entrée serving size in each condition was different for each age group. This approach allowed each child to serve as his/her own control, where each child's intake in the large portion condition was directly compared with his/her intake in the reference condition. More importantly, the use of change scores allowed the separation of portion size effects from age-related differences in absolute intake that were inherent to the design.

The direct contribution of large food portions to overweight among children is not known. Huang et al. (11) reported a positive association of mean meal portion size (measured by grams of foods and beverages) with BMI for male children 6 to 11 years old and for male and female adolescents 12 to 19 years old, although not for 3- to 5-year-old children. However, causal inferences cannot be drawn from cross-sectional observational research, and ethical considerations prohibit conduct of the relevant experimental studies in children. The single-meal design of this research was clearly not appropriate to evaluate this question. However, to the extent that the children's intake in the laboratory represented a characteristic response to large portions, these data provide insight as to whether overweight children are particularly susceptible to overconsuming large portions. Consistent with previous laboratory studies of portion size in children (7, 8) and adults (21, 22), this study failed to observe an association of weight status with children's intake of large entrée portions. Similarly, maternal weight and overeating did not explain individual differences in children's intake of large entrée portions. Collectively, the experimental findings suggest that the tendency to overconsume large portions is not unique to overweight children or adults. As such, the contribution of large portions to high energy intake and positive energy balance among children may be explained principally by the extent of children's habitual exposure to large food portions rather than by a particular susceptibility per se of the overweight child to overeat. Prospective studies that quantify children's exposure to large portions and associate exposure with energy intake and weight gain are needed to clarify the relationship between exposure to large food portions and overweight among children.

The capacity of large portions to promote intake in both male and female children of varying ages and body weights raises the question of potential mechanism. Some have argued that large food packaging, food vessels, and portion sizes promote selection and consumption in adults by conveying greater expected consumption norms (23, 24, 25). In this case, visual cues provided by larger food portions are believed to implicitly reinforce greater consumption as being normative or appropriate. Behavioral observations made in the present study, however, suggest that children were unlikely to be affected by such norms because they were relatively unaware of the increases to entrée portion size. Furthermore, the notion that the findings reflected a motivation to clean the plate seems unlikely given that children consumed, on average, only 56% of the reference portion. The fact that entrée intake was uncorrelated among children sitting at the same table would also seem to argue against the facilitation of such norms through social processes (23).

Studies of spatial perception suggest that perceptual cues regarding the amount of food available might also explain portion size effects on children's intake. Increases in size tend to be underestimated, and the magnitude of the perceptual error grows as the size increases (26, 27). Piaget et al. (28) showed that, before age 8, young children have difficulty recognizing that the quantity of a given amount of liquid does not change when transferred from a shorter container to a taller narrower container. It has since become clear, however, that such volume illusions (29) alter portion selection and consumption of liquids even among adolescents (30) and adults (31). For instance, adolescents were served and consumed ∼75% more juice when using a short (10.6 cm), wide glass than a taller (18.9 cm), narrower glass of the same volume capacity (22.3 oz) (30). In this research, visual cues pertaining to the amount of food on the plate may have similarly increased consumption by altering the microstructure of eating.

As in Fisher et al. (8), the total number of bites children took of the entrée did not differ in the reference and large portion conditions. However, the large entrée produced a significant increase in the average entrée bite size relative to the reference portion. The manner by which portion size affects bite size is not well described. Among adult men and women, Lawless et al. (32) observed an increase of 15% in the average amount of water taken into the mouth per sip across conditions in which 150-, 300-, and 600-mL cup sizes were presented. In another study of adult men, the number of grams ingested per chew varied widely across foods provided ad libitum at a meal, ranging from ∼2 to 14 g/chew. Although not discussed in the report, the magnitude of those values seemed to be ordered with the size of the unit food provided (i.e., grams ingested per chew for sandwich > cake > bagel > cookie > chip) (33). A post hoc analysis of the data in this experiment provided similar results, revealing that bite size increased across the full range of entrée serving sizes used (200 to 900 grams).

Increases in bite size were observed both for children who ate more of the entrée when served the large portion and for those who did not. Children who ate the same or less when served the large portion, however, actually took fewer total bites of the large portion entrée than the reference portion entrée. Whether variation in the total number of bites taken in this research reflected differences in children's self-regulatory abilities is not possible to determine. In animal and human studies, experimentally produced increases in lick volume or bite size were not only accompanied by higher average ingestion rates (grams ingested per minute) and greater chew efficiencies (grams per chew) but also by compensatory decreases in the total number of bites taken, such that meal size was not affected (34, 35). Clearly, further study of visual perception on ingestive behavior is needed to more fully understand the manner in which portion size alters the microstructure of eating.

Finally, in contrast to the findings of Fisher et al (8), an intake-reducing effect of self-selection was not apparent in the sample as a whole. Rather, allowing children to determine portion size seemed to benefit only those children who tended to overeat when served the large portion entrée. Those children consumed 17% less of the entrée and 11% less total energy at the meal when allowed to self-serve than when the large portion was served to them. These findings, in conjunction with those of previous research, indicate that allowing children to self-select portion size may prevent excessive intake among children who are prone to overeating when served large portions.

As in the previous studies (7, 8), this study used an amorphous macaroni and cheese entrée. It is unclear whether the findings generalize to other types of foods, particularly unit foods (e.g., sandwiches, cookies, chicken nuggets, etc.) for which portion size may be relatively easier to discern. Similarly, whether portion size effects on children's eating vary with food energy density is not known. In studies of adults, food energy density and portion size have combined effects on energy intake (36). The energy density of the entrée used in this research was 1.4 kcal/g, indicating a relatively low-energy density (37). It is possible that total energy intake at the meal may have been higher had an entrée of greater energy density been used. Specific to the interpretation of age-related effects is the consideration that the entrée reference portion for 8- to 9-year-old children was considerably larger than that specified for the other groups. Assuming a linear effect of portion size on intake, it is possible that the relatively large reference portion served to the oldest children produced ceiling effects on entrée intake and consequently limited the ability to observe age-related effects. However, the fact that the proportion of the reference entrée consumed did not differ by age group argues against this interpretation, and it may be that the assumption of a linear relationship of portion size and intake is false.

In summary, the results of this study show intake-promoting effects of serving large entrée portions at meals among 2- to 9-year-old children. Younger preschool-age children did not seem to be protected against portion size effects as in previous research (7). The absence of a strong age effect on children's intake of large entrée portions, however, does not preclude the possibility of an age effect in compensation observed beyond a single meal. High levels of energy intake among children are likely produced by a complex set of environmental, social, economic, and behavioral factors, acting on a background of genetic susceptibility (38, 39), occurring in familial and societal contexts that interact with age (39). Nor do the findings of this research rule out the possibility that sensitivity to internal regulatory cues generally decreases with age. Indeed, preschool-age children have shown a more precise regulation of short-term energy intake than adults in laboratory experiments (5). A recent experiment observed that younger school-aged children (6 to 7 years) showed more precise compensation than older children (8 to 9 years) (40). Rather, the results of this research confirm that environmental agents can modify self-regulatory controls of energy intake at early points in development and suggest that any developmental differences in children's susceptibility to overeating large food portions are likely of a magnitude smaller than previously suspected. A potentially protective effect of allowing children to self-determine portion size warrants further empirical inquiry to determine how children arrive at customary portions.

Acknowledgments

  1. Top of page
  2. Abstract
  3. Introduction
  4. Research Methods and Procedures
  5. Results
  6. Discussion
  7. Acknowledgments
  8. References

This research was funded by the North American International Life Sciences Association Committee on Lifestyle and Weight Management. The author thanks Wendy Tovar, Fely Aguilar, and the staff of the United States Department of Agriculture/Agriculture Research Service Children's Nutrition Research Center Metabolic Research Unit for collecting these data.

References

  1. Top of page
  2. Abstract
  3. Introduction
  4. Research Methods and Procedures
  5. Results
  6. Discussion
  7. Acknowledgments
  8. References
Footnotes
  1. The costs of publication of this article were defrayed, in part, by the payment of page charges. This article must, therefore, be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.