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1 From the Stanford Prevention Research Center, Stanford University School Of Medicine, Stanford, CA.
2 Supported by grant no. 5-R01 HL54102 from the National Heart, Lung, and Blood Institute; grant no. 99-00530V-10173 from the California Department of Health Services, Cancer Research Program; and a Robert Wood Johnson Foundation Generalist Physician Faculty Scholar Award (to TNR). 3 Address reprint requests to DM Matheson, Stanford Prevention Research Center, Stanford University School of Medicine, Hoover Pavilion, Room N229, 211 Quarry Road, Stanford, CA 94305-5705. E-mail: matheson{at}stanford.edu.
ABSTRACT
Background: Television viewing is associated with childhood obesity. Eating during viewing and eating highly advertised foods are 2 of the hypothesized mechanisms through which television is thought to affect children’s weight.
Objectives: Our objectives were to describe the amounts and types of foods that children consume while watching television, compare those types with the types consumed at other times of the day, and examine the associations between children’s body mass index (BMI) and the amounts and types of foods consumed during television viewing.
Design: Data were collected from 2 samples. The first sample consisted of ethnically diverse third-grade children, and the second consisted predominantly of Latino fifth-grade children. Three nonconsecutive 24-h dietary recalls were collected from each child. For each eating episode reported, children were asked whether they had been watching television. Height and weight were measured by using standard methods and were used to calculate BMI.
Results: On weekdays and weekend days, 17–18% and 26% of total daily energy, respectively, were consumed during television viewing in the 2 samples. Although the fat content of the foods consumed during television viewing did not differ significantly from that of the foods consumed with the television off, less soda, fast food, fruit, and vegetables were consumed with the television on. The amount of food consumed during television viewing was not associated with children’s BMI, but in the third-grade sample, the fat content of foods consumed during television viewing was associated with BMI.
Conclusions: A significant proportion of children’s daily energy intake is consumed during television viewing, and the consumption of high-fat foods on weekends may be associated with BMI in younger children.
Key Words: Childhood obesity • dietary intake • television viewing • dietary recalls • multiethnic population • children
INTRODUCTION
Television viewing has been associated with childhood obesity in several epidemiologic studies (1). In a clinical trial, third- and fourth-grade children who received intervention to reduce television viewing had lower body mass index (BMI; in kg/m2) values, tricep skinfold thicknesses, waist circumferences, and waist-to-hip ratios than did control subjects (2). Children who received the television-reduction intervention reduced the number of meals consumed during television viewing, and a trend toward lower intakes of high-fat foods was observed. Two of the hypothesized mechanisms through which television viewing is thought to promote childhood obesity are increased dietary intake from eating during viewing and eating highly advertised foods (1). Several studies provided ecologic evidence in support of these mechanisms. First, increased television viewing has been associated with increased energy intake (3–5). Adolescents who reported watching more television also reported eating more high-fat foods (6) and fast food, drinking more soft drinks, and consuming fewer fruits and vegetables (4). Likewise, in households in which the television is on during meals, children consume more red meat, pizza, snack foods, and soda and fewer fruits and vegetables (7). Second, several content analyses of children’s television programs showed that foods, especially high-fat or high-sugar foods, are frequently advertised on children’s television programs (8–11). Furthermore, an experiment conducted with preschool children showed that only a brief exposure to food advertisements embedded within children’s programming resulted in the children choosing the advertised brand of food over a similar unadvertised product (12). Prior studies of the effects of food advertising on older children’s food choices showed similar effects (13, 14).
Most previous epidemiologic research investigating the relation between television viewing and dietary intake has relied on separate reports of daily television viewing practices and dietary intake. Data on what children actually eat during television viewing are lacking. Therefore, during 24-h dietary recalls, we collected data on the activities that children participated in while they ate each meal or snack. We used these data to describe the amount and types of foods consumed during television viewing, to examine the association between these types of foods and children’s BMI, and to compare the types of foods that children consumed when the television was on with the types of foods that they consumed when the television was off.
SUBJECTS AND METHODS
Subjects
Data were collected from 2 different samples. All data were collected in 1999–2000 by using the same methods. Both studies were approved by the Stanford University Panel on Human Subjects in Medical Research.
Sample 1
The first sample was drawn from children participating in a school-based randomized clinical trial on reducing television viewing. Twelve elementary schools from 2 ethnically diverse elementary school districts in northern California participated in this study. All third-grade children enrolled in the schools in September 1999 were eligible to participate. During telephone interviews, parents were informed of the opportunity to participate in 24-h dietary recalls and physical activity monitoring. If they were interested in having their child participate, they were mailed information, including a consent form, and contacted to schedule an initial interview. All children recruited at baseline (fall 1999) and additional children from the same 12 schools who were recruited into the control group during the spring 2000 data-collection period were included in the sample. This sample is referred to as the third-grade sample.
Sample 2
The second sample was drawn from a cross-sectional study of environmental factors affecting children’s dietary intake that was part of a school-based clinical trial to reduce obesity. Fifth-grade students enrolled in 8 low-income elementary schools in San Jose, CA, participated in this project. The students’ mothers were contacted at school events and through telephone solicitation. The families of the children enrolled in these schools were primarily Mexican American and low income. Written informed consent was obtained from the children and their mothers during the first interview. This sample is referred to as the fifth-grade sample.
Measures
Dietary intake
Three nonconsecutive 24-h dietary recalls that included 2 weekdays and 1 weekend day were conducted, and the children were the primary respondents. Nine validation studies have provided support for the use of 24-h dietary recalls in children as young as third-grade children (15–23), and 24-h dietary recalls are considered the most appropriate method to collect dietary data from diverse cultural groups (24). Registered dietitians collected the recalls by using standard protocols in the Nutrition Data System for Research (NDS-R, versions 4.01 and 4.02) (25). In addition, for each meal or snack, the children were asked whether they participated in any of the following activities while eating: watching television, watching a videotape or movie on a videocassette recorder or video disk, playing video games or playing on a computer, watching a movie at the theatre, doing homework, reading (other than for homework), playing inside, playing outside, or riding in a car, van, bus, or truck. This information was linked to the data on the foods and nutrients consumed during each meal or snack. The first recall was conducted face-to-face, and the remaining 2 recalls were collected over the telephone. The children’s mothers were consulted on both the face-to-face and telephone recalls to clarify food details, food-preparation methods, or brand names that the children could not recall. To check the interinterviewer reliability of the dietary recalls, a subsample of 22 (5%) telephone recalls were tape-recorded and reentered by a second dietitian.
The NDS-R database (versions 4.01 and 4.02) is derived from the US Department of Agriculture Handbook No. 8 and includes many Hispanic food items (26). Average intakes of energy; percentages of energy from fat; energy densities; and average intakes of soda, children’s cereals, sweets and snack foods, fast foods, and fruit and vegetables were calculated. Energy density calculations included all foods and all beverages with >1.20 kJ/serving. Soda included all varieties of soda, both diet and regular. Children’s cereals included those that had a character designed to appeal to children on the box. Sweets and snack foods included ice cream, doughnuts, cookies, cakes, pies, candy, chips, popcorn, crackers, pretzels, and other salty snack foods. Fast foods included all foods and beverages purchased from national fast food restaurant chains. Fruits and vegetables were defined according to the 5-A-Day criteria (27). Accordingly, fresh, frozen, or canned fruit and 100% fruit juices were included, but fruit dishes that contained >30% of energy from fat were not included. Likewise, vegetables included all fresh, frozen, or canned vegetables. Fried or pickled vegetables and vegetable dishes that contained >30% of energy from fat were not included.
Height and weight
Standing height without shoes was measured twice, to the nearest millimeter, by using a portable, direct-reading stadiometer. If the 2 measures differed by >5 mm, a third measure was obtained. Body weight was measured twice, to the nearest 0.1 kg, by using digital scales while the subjects wore light indoor clothing but no shoes. If the 2 measures differed by >0.2 kg, a third measure was obtained. The mean of the 2 measures, or the median of the 3 measures, was used in the analysis. BMI was calculated as weight (in kg) divided by the square of height (in m).
Demographic variables
In the third-grade sample, the parents reported their children’s age, sex, and ethnicity during telephone interviews. In the fifth-grade sample, the mothers reported this information during a face-to-face interview.
Statistics
Because the children were sampled from 2 different populations, all analyses were calculated independently for each sample. Prior to our primary analyses, we examined weekday–weekend day effects by using multilevel analysis of variance, which showed significant heterogeneity (defined a priori as P < 0.10) between weekend days and weekdays in energy intake and percentage of energy from fat with the television on or off in both samples (F ranged from 3.57 to 15.16, all P < 0.06). Therefore, all subsequent analyses were performed separately for weekend day and weekday data, or effects for weekend day compared with weekday were included in the analyses. The average of the 2 weekdays were used in all weekday analyses.
First, the amount of food consumed during television viewing was described by the number of meals consumed with the television on or off, the amount of energy consumed with the television on or off, and the number of servings, based on standard US Department of Agriculture serving sizes, of foods in each of the 6 food categories that were consumed during television viewing. A paired sample sign test was used to examine differences in the percentage of meals consumed during television viewing between weekdays and weekend days. To examine the association between children’s food consumption during television viewing and their weight status, Spearman correlations were calculated between BMI and both percentage of total energy consumed with the television on and percentage of total energy from fat consumed with the television on.
Second, we examined the types of foods consumed during television viewing, the differences between the types of foods consumed with the television on or off, and the associations between the types of foods consumed during television viewing and children’s weight status. The types of foods consumed with the television on or off were described by the percentage of energy from fat, the energy density (kilojoules per gram of food or beverage containing >1.20 kJ/serving), and the percentage of energy that each of the 6 food categories contributed to the total amount of energy consumed with the television either on or off. To assess the relation between the types of foods consumed during television viewing and children’s weight status, Spearman correlations were calculated between children’s BMI and both the percentage of energy from fat consumed during television viewing and energy density of foods consumed during television viewing for the subsample of children who consumed any food while watching television. Finally, two-factor repeated-measures analysis of variance was used to examine differences in the types of foods consumed with the television on or off and in the types of foods consumed on weekdays and weekend days and the interaction between the types of foods consumed with the television on or off on weekdays and weekend days. All analyses were conducted by using SAS version 8.02 (SAS Institute Inc, Cary, NC).
RESULTS
Sample characteristics
Sample 1
At baseline, 639 families were informed of the 24-h dietary recall data collection for the study during parent telephone interviews. Of these families, 350 expressed interest in participating in the recalls, and 64 children completed 3 recalls. Of the 350 families who expressed interest in participating in the recalls, 234 families were called at least once, 116 were not called because of limits on the number of weeks spent on baseline data collection, 99 families did not schedule an interview because of these time restraints, 66 refused to make the initial appointment when they were contacted, 3 had moved, and 2 had disconnected phone numbers. At posttest, dietary recalls were collected from an additional 60 children whose families had expressed interest in participating in the 24-h dietary recall data collection at baseline but were unable to schedule a data-collection appointment during the baseline data-collection period. From the 12 schools from which the original subjects were drawn, 27 additional children were randomly assigned as control subjects. Therefore, our total sample consisted of 91 children who had 3 dietary recalls (98% had one weekend day and 100% had 2 weekdays), and of these children, 90 had complete physical measurements (Figure 1). In the final sample, 57.1% of the subjects were girls, and the average age of the children was 8.6 y (range: 7.8–9.6 y.) More than one-third of the families (39.6%) identified their ethnicity as Latino, 24.2% as white, 19.8% as Filipino, 6.6% as Asian, 4.4% as African American, and 4.4% as multiethnic. The mean (± SD) BMI of the sample was 18.6 ± 3.4 (range: 13.5–27.2).
FIGURE 1.. Flow chart of sample 1 recruitment.
Sample 2
A total of 178 families were contacted regarding this study. One hundred thirty families agreed to participate, and 129 children provided 3 dietary recalls (95% had 1 weekend day, and 100% had 2 weekdays). Of these children, 124 also had complete physical measurements. In this sample, 46.5% of the subjects were girls, and the average age of the children was 9.6 y (range: 9.0–11.5 y). Most of the families identified their ethnicity as Latino (86.8%), but the other families identified their ethnicity as Pacific Islander (9.1%), white (1.7%), Asian (1.7%), and African American (0.8%). The mean (± SD) BMI of the sample was 20.70 ± 4.17 (range: 13.10–36.81).
Total amount of food and energy consumed daily during television viewing
Food was consumed more often during television viewing, which included the viewing of television shows, movies, or videotapes on a videocassette recorder, than while participating in other activities. Specifically, <3% of total daily energy was consumed in each of the other 8 activity categories: playing video games or playing on a computer, watching a movie at the theatre, doing homework, reading (other than for homework), playing inside, playing outside, or riding in a car, van, bus, or truck. Therefore, these categories were combined with the category "just eating" and labeled "not watching television" or "television off." The average energy intake during television viewing was similar in both samples and was higher on weekend days than on weekdays. In the third-grade sample, 16.6 ± 16.4% (
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TABLE 1. Children’s daily dietary intakes with the television (TV) on or off on weekdays and weekend days1
The percentages of meals and snacks consumed during television viewing are reported in Table 2. Mean values for each child’s 2 weekday dietary recalls were first calculated and were then used to calculate sample means. Snacks, especially on weekdays, were consumed more frequently during television viewing than were any of the meals. More than one-third of the children’s dinners were consumed in front of the television. As expected, lunch on weekdays was rarely consumed during television viewing because the children were likely in school. In both samples, television viewing during breakfast and lunch was significantly higher on weekend days than on weekdays, and in the fifth-grade sample, television viewing during snacks was significantly lower on weekend days.
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TABLE 2. Percentages of meals and snacks consumed during television viewing on weekdays and weekend days1
The associations between children’s BMI and the percentages of total daily energy and fat consumed during television viewing are reported in Table 3. None of these correlations were significant.
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TABLE 3. Spearman correlations of children’s BMI with average percentages of total daily energy and fat consumed during television viewing1
To examine whether children eat qualitatively different types of foods during television viewing than during other times of the day, we compared the percentage of energy from fat, energy density, and the percentage of energy that each food type contributed to meals or snacks when the television was on with the same variables when the television was off both on weekend days and weekdays (Table 4). In both the third-grade and fifth-grade samples, there were no significant differences between the percentage of energy from fat and the energy density of foods consumed during television viewing and those of foods consumed at other times on either weekdays or weekend days. In the third-grade sample, soda, fast food, and vegetables were significantly less likely to be consumed during television viewing than during other times. Also in the third-grade sample, fruit was significantly less likely to be consumed during television viewing on weekdays than on weekend days, and soda was significantly less likely to be consumed on weekdays. The children in the fifth-grade sample consumed a significantly higher percentage of energy from fat on weekend days than on weekdays. In the fifth-grade sample, vegetables and sweets and snack foods were significantly less likely to be consumed during television viewing than during other times. On weekdays, soda was significantly more likely to be consumed during television viewing than during other times of the day, but on weekend days, soda was significantly less likely to be consumed during television viewing than during other times. In addition, these fifth-grade children were significantly more likely to consume fast food and vegetables but significantly less likely to consume fruit on weekend days.
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TABLE 4. Percentages of energy from fat, energy densities, and percentages of energy from various types of foods consumed with the television (TV) on or off on weekdays and weekend days1
Associations between BMI and both the percentage of energy from fat and the energy density of foods consumed during television viewing are reported in Table 5. Only the children who ate while watching television were included in this analysis. In the third-grade sample’s weekday data, the correlation between the children’s BMI and the percentage of energy from fat consumed during television viewing was significant (r = 0.25, P = 0.04; n = 66), and the correlations between the energy density of foods consumed during television viewing and BMI for the weekdays and weekend days were similar in magnitude but not significant [r = 0.23 (P = 0.06) for weekdays, and r = 0.21 (P = 0.13) for weekend days]. BMI was not significantly correlated with the percentage of energy from fat or the energy density of foods consumed during television viewing in the fifth-grade sample.
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TABLE 5. Spearman correlations of children’s BMI with percentage of energy from fat and energy density of foods consumed during television viewing
DISCUSSION
This is the first study to examine how much food and what types of foods children eat while watching television. Our results show that children consume a substantial proportion of their daily energy while watching television. Food consumption during television viewing differs between weekend days and weekdays, and therefore weekend-weekday differences must be considered both in the design of studies of food consumption during television viewing and in the analysis of the data generated by such studies. On weekend days, more than one-quarter of the children’s daily energy was consumed during television viewing, and on weekdays, nearly 20% of daily energy was consumed during television viewing. These results were highly consistent across 2 qualitatively different samples of children. Accordingly, eating while watching television may be an important behavior to target in interventions designed to alter children’s overall food intake.
There were no significant differences between the fat content and energy density of foods consumed with the television on and those of foods consumed with the television off. This result is consistent with that of previous ecologic research in which no total nutrient differences were found between the overall diets of children who consumed >2 meals/d while watching television and those of their peers who consumed <2 meals/d watching television (7). However, in the present study, there were some differences in the relative energy contributions of some types of foods between times of television viewing and other times of the day. Specifically, in both samples, the percentage of energy from vegetables consumed during television viewing was significantly lower than that from vegetables consumed at other times during the day. Children’s preferences for vegetables are generally low (28); thus, if children are given a choice, they may be less likely to choose vegetables over other foods. Furthermore, snacks were consumed more frequently during television viewing than were any of the meals, and children may have more autonomy or choice in their snacks than in their meals. Accordingly, children may not choose vegetables for snacks during television viewing.
Although advertising has been shown to influence children’s food choices (12–14), our results do not support the hypothesis that children consume more highly advertised foods while watching television. In the diverse third-grade sample, significantly less soda and fast food were consumed on weekdays during television viewing than during other times of the day, and in the mostly Latino fifth-grade sample, significantly less soda and significantly fewer sweets and snacks were consumed on weekend days during television viewing than during other times of the day. These results are counter to those of previous research that showed that more soda, snack foods, and pizza were consumed by children in households in which the television was on for >2 meals/d (7), and this discrepancy in results highlights the differences between the ecologic study design and our direct correlation design.
In the third-grade sample, the type, but not the amount or frequency, of foods consumed during television viewing was associated with the children’s current weight status. The children who consumed more energy from fat while watching television had higher BMI than did their peers who consumed fewer high-fat foods with the television on. A post hoc analysis showed no significant correlations between the number of servings from each food category consumed during television viewing on weekdays and the children’s BMI, but on weekends, soda consumption during television viewing was significantly associated with BMI (r = 0.26, P < 0.01).
There are some limitations to the methods used in these studies. First, although 24-h dietary recalls are recognized as the best method to estimate dietary intake in children (15–22, 29) and are the most appropriate method to determine what children eat while watching television, the intraindividual variation in dietary intakes makes multiple recalls necessary to accurately estimate energy intake (30). However, prior to our primary analysis, we detected weekend-weekday differences in food consumption with the television on or off and, therefore, analyzed weekend and weekday data separately for each child. Accordingly, only one weekend recall and 2 weekday recalls were included in the analysis, which may have limited the reliability of the food and nutrient estimates and reduced the power to detect differences. The fat intakes reported by both samples were relatively low and may have reflected the children’s inability to report dietary intake, especially fat intake, or this finding may show true regional or ethnic differences in fat consumption.
Second, the samples were too small for analysis of differences in sex or ethnicity, and pooling data from heterogeneous samples increases the risk of invalid results (31, 32). For example, the 2 samples differed notably in vegetable intake. The fifth-grade children were from low-income, Latino homes in which beans, which were classified as a vegetable, were staple foods, and therefore their vegetable intake was significantly higher than that of the third-grade sample. The correlational results also differed between the 2 samples, so pooling the samples would likely obscure the differences in these relations and lead to misleading conclusions. Therefore, this research should be replicated in a large multiethnic sample.
In sum, this study shows that a significant proportion of children’s daily energy is consumed during television viewing, and the consumption of high-fat foods during television viewing on weekdays was associated with BMI in the third-grade sample. These findings support the speculation that eating while watching television is a potential mechanism linking television viewing to obesity. These results serve to justify future experimental studies to test this hypothesis. Interventions designed to help children change the types of foods consumed during television viewing, reduce food consumption during television viewing, or even reduce television viewing may markedly change children’s dietary intake patterns (33).
ACKNOWLEDGMENTS
We thank Helena C Kraemer for statistical advice and Kara Hansen, Jennifer Styles, Melissa Saphir, Andrea Romero, and Rebecca Brown for assistance with data collection.
DMM was responsible for the design of the study, collection of the data, and the writing of the manuscript. JDK contributed to the design of the study and the securing of funding. YW and AV were responsible for data analysis and provided statistical advice. TNR was responsible for the securing of funding, the design of the study, and the writing of the manuscript. None of the authors had advisory board affiliations or financial interests in the organizations sponsoring the research.
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