Physical Activity, Aerobic Fitness, Self-Perception, and Dietary Intake in At Risk of Overweight and Normal Weight Children
Posted on: Monday, 3 October 2005, 12:00 CDT
By Ball, Geoff D C; Marshall, J Dru; McCargar, Linda J
Abstract
Differences in physical activity, aerobic fitness, self- perception, and dietary intake were examined in a sample of six- to ten-year-olds at risk of overweight, and m normal weight boys and girls. Participants (n=20 at risk of overweight [BMI ≥85th percentile]; n=115 normal weight [BMI <85th percentile]; n=68 boys; n=67 girls) had anthropometric, physical activity, aerobic fitness, self-perception, and dietary intake measurements at zero, three, six, and 12 months. Over the 12-month period, normal weight children were more physically active (F=4.1, p<0.05) and aerobically fit (F=14.3, p<0.001), and possessed higher self-perceptions of social acceptance (F=7.3, p<0.01) than their at risk of overweight peers. Fitness differences between the sexes were not apparent at baseline, but emerged over the long term (F=7.9, p<0.01). Overall, boys consumed more total energy, fat, carbohydrate, and protein than did girls, while the entire sample consumed diets low in vegetables and fruits and meat and alternatives, and high in "other" foods. These observations highlight key disparities in lifestyle-related behaviours and perceptions between groups of children according to overweight status and sex. The findings underscore the importance of longitudinal studies in youth because cross-sectional studies may reflect transient differences.
(Can J Diet Prac Res 2005;66:162-169)
Rsum
Les diffrences relatives l'activit physique, la condition arobie, la perception de soi et l'apport alimentaire ont t examines chez un chantillon d'enfants de 6 10 ans risque de souffrir d'embonpoint et chez des garons et filles de poids normal. Les participants (n=20 risque d'embonpoint [IMC≥85^sup e^ percentile]; n=115 de poids normal [IMC<85^sup e^ percentile]; n=68 garons; n=67 filles) ont t soumis des mesures anthropomtriques et des mesures de l'activit physique, de la condition arobie, de la perception de soi et de l'apport alimentaire avant la priode exprimentale, puis 3, 6 et 12 mois du dbut de la priode exprimentale. Au cours de la priode de 12 mois, les enfants de poids normal taient plus actifs physiquement (F=4,1, p<0,05), plus en forme sur le plan arobie (F=7,3, p<0,001) et avaient une perception plus positive de leur acceptation sociale (F=7,3, p<0,01) que leurs pairs risque d'embonpoint. Les diffrences dans la forme physique entre les sexes n'taient pas apparentes au dpart, mais se sont rvles long terme (F=7,9, p<0,01). Dans l'ensemble, les apports en nergie totale, matires grasses, glucides et protines taient plus levs chez les garons que chez les filles, tandis que tous les sujets de l'chantillon ont consomm une alimentation faible en lgumes, fruits, viande et substituts, et riche en d'autres aliments. Ces observations mettent en relief les diffrences cls dans les comportements et perceptions lis au mode de vie entre les groupes d'enfants selon leur tat pondral et leur sexe. Les rsultats font ressortir l'importance d'tudes longitudinales chez les jeunes, car les tudes transversales peuvent reflter des diffrences transitoires.
(Rev can prat rech ditt 2005;66:162-169)
INTRODUCTION
The prevalence of overweight among Canadian children has increased dramatically over the past two decades. Currently, an estimated 29.2% of girls and 35.4% of boys are overweight (body mass index [BMI] ≥85th percentile), while 14.6% of girls and 16.6% of boys are obese (BMI ≥95th percentile) (1). This high level of overweight in childhood is cause for concern because increased levels of body fat are known to persist from youth to adulthood (2), and because heavier children are more likely than their leaner peers to possess risk factors for chronic disease (3,4). Such observations may explain the increased risk of morbidity and mortality seen among overweight children who become overweight and obese adults (5). The evidence linking increased weight with unfavourable levels of objective physical health indicators is well supported. However, findings are equivocal when health-related behaviours and perceptions are contrasted according to weight status, especially in younger populations.
Some research suggests that boys and girls with higher levels of body fat consume more total energy (6,7) and dietary fat (8,9), and are less physically active (10,11) and aerobically fit (12) than leaner children. Other studies have failed to show differences in diet (13,14) and physical activity (15) in children stratified by weight status. Although overweight children generally are believed to have lower self-esteem than their normal weight peers, this belief has not been consistently supported in the literature. French and colleagues (16) concluded in their review that overall self- esteem levels in overweight seven- to 12-year-olds were either similar to or just slightly lower than those of normal weight boys and girls.
Because most data linking body fatness in youth with unfavourable lifestyle behaviours and perceptions are derived from cross- sectional investigations, relationships between overweight and lifestyle variables may be transitory. This is a plausible theory because many health-related behaviours and attitudes are established in childhood (17). Thus, the purpose of this study was to examine differences in physical activity, aerobic fitness, self-perception, and dietary intake in a sample of six- to ten-year-olds at risk of overweight, as well as in normal weight boys and girls at zero-, three-, six-, and 12-month intervals.
METHODS
Participants
Thirteen teachers from a convenience sample of seven Edmonton- area elementary schools were asked to have their classrooms (grades 2 to 4) participate in this investigation; the research was not a component of class curricula and participation was voluntary. Parents and children provided informed consent and assent, respectively. Approval for this project was obtained from the University of Alberta Faculty of Agriculture, Forestry and Home Economics human ethics review committee, the Cooperative Activities Program, and the Edmonton Public and Catholic School Districts.
Procedures
Skinfold-thickness measurements were taken at five sites (triceps, biceps, subscapular, suprailiac, and calf) on the right side of the body using Harpenden skinfold calipers (Health Dimensions, Plymouth, MI). Height was assessed to the nearest 0.1 cm using a set square and a wall-mounted tape measure, and weight was determined to the nearest 0.1 kg using a portable medical scale (Health o meter, Inc., Bridgeview, IL); BMI (kg/m^sup 2^) was subsequently calculated. Children were classified as at risk of overweight (BMI ≥ 85th percentile) or normal weight (BMI <85th percentile) according to the United States Centers for Disease Control and Prevention growth charts (18). Body mass index percentiles were calculated using Epi Info 2002, version 2. All data were collected using Canadian Standardized Test of Fitness procedures (19).
Table 1
Baseline anthropometric comparisons between at risk of overweight and normal weight groups, and boys and girls
Physical activity level was assessed using the Physical Activity Questionnaire for Older Children (PAQ-C), a self-administered, seven- day activity recall that evaluates sports, leisure activities, and games performed during school days, evenings, and weekends (20). The 20-metre shuttle run test (20-MST) was used to determine aerobic fitness levels (21). The test requires subjects to run back and forth between two markers spaced 20 m apart; as the test advances, the time interval between signals decreases so that running speed must increase progressively.
Self-perception was measured using the Self-Perception Profile for Children (SPPC) (22-24). The SPPC consists of the following sub- scales that collectively influence overall self-esteem: scholastic competence, social acceptance, athletic competence, physical appearance, behavioural conduct, and global self-worth. Higher scores represent more positive ratings of self-perception.
The 24-hour dietary recall was used to estimate dietary intake. Detailed written instructions and a completed sample recall were provided to families. Boys and girls completed the instrument at home with their parents; teachers collected the forms the following day. Two registered dietitians (RDs) telephoned families within one week of the recall day to review and confirm the data with parents (25,26). Nutrition data were collected using the multiple-pass technique (25). Retrieving data for all days of the week was not possible for practical reasons (i.e., holidays and field trips). Forms were distributed to classrooms from Monday to Friday, so information was recorded on five days of the week only (Sunday to Thursday). An RD used the Food Processor for Windows (ESHA Research, version 7.02, Salem, OR, 1997) to analyze the data.
?Statistics
At baseline, the effects of overweight status (at risk of overweight, normal weight) and sex and overweight status sex interaction were evaluated using a 2 2 multivariate analysis of variance (MANOVA). Significant MANOVA results were followed up with pair-wise comparisons on the dependent variables. Longitudinally, a 2 2 4 repeated measures analysis of variance (ANOVA) mod\el was used to assess differences m each independent variable across overweight status and sex at zero, three, six, and 12 months. Because aerobic fitness and self-perception sub-scale data were not normally distributed, these values were log-transformed before analysis. The number of servings of grain products, milk products, meat and alternatives, vegetables and fruit, and other foods (27) was adjusted for total energy intake before analyses. All data are expressed as means standard deviation, and statistical analysis was performed using the Statistical Package for the Social Sciences (SPSS Inc., version 7.5, Chicago, IL, 1995), with significance set a priori at p<0.05.
RESULTS
Subject participation
Overall, 136/276 (49.1%; 92% Caucasian) children agreed to participate in the study. One child moved out of the area during the year, so these analyses were based on complete data collection from the remaining sample (n=135). Socioeconomic status was not formally assessed, but school principals considered the participating schools to be located in middle-class to upper-middle-class neighbourhoods.
Weight classifications
Those children who possessed a BMI at or above the 85th percentile at all four measurement intervals (zero, three, six, and 12 months) were included m the at risk of overweight group (n=20; 11 boys, nine girls). This cohort was compared with a normal weight group (n= 15; 57 boys, 58 girls) comprising children who did not consistently have a BMI at or above the 85th percentile. Cross- sectionally, some children were categorized as at risk of overweight at one, two, or three time points and were subsequently included in the normal weight group. Because the inclusion of "transiently" at risk of overweight children (n=23) in the normal weight group may have affected our findings, we also compared the at risk of overweight cohort with those children who were never at risk of overweight (n=92). Ultimately, our results did not differ when the at risk of overweight group was compared with either the normal weight (n=115) or the never at risk of overweight (n=92) group. Thus, we included data from all participating children m our analysis.
Table 2
Baseline lifestyle-related behaviour comparisons between at risk of overweight and normal weight groups, and boys and girls
Baseline findings
Anthropometry: At risk of overweight children were heavier, possessed higher absolute BMI and BMI percentile scores, and had a greater sum of five skinfolds than did their normal weight peers (all p<0.001) (Table 1). Boys were taller, heavier, and had a smaller sum of five skinfolds (all p<0.05).
Activity, fitness, and self-perception: For the physical activity, aerobic fitness, and self-perception variables, a main effect of overweight status (F=2.0, p<0.05) was found. Univanate analyses revealed that at risk of overweight children had lower levels of self-reported physical activity (p<0.01), aerobic fitness (p<0.01), and social acceptance (p<0.05) than did their normal weight peers (Table 2).
Diet: For the dietary variables (Table 3) there was no mam effect for overweight status (F=11, p=0.40), but there was for sex (F=4.0, p<0.001). Overall, boys had a higher total energy intake (p<0.01) and consumed more absolute fat (p<0.05), carbohydrate (p<0.05), and protein (p<0.001).
Table 3
Baseline dietary intake (24-hour recall) comparison between at risk of overweight and normal weight groups, and boys and girls
Longitudinal findings
Anthropometry: Normal weight children consistently weighed less (F=68.4, p<0.001), had a lower absolute BMI (F=136.3, p<0.001), a lower BMI percentile (F=69.5, p<0.001), and a smaller sum of five skinfolds (F=125.0, p<0.001) in relation to at risk of overweight children. In addition, boys remained taller (F=5.5, p<0.05) and possessed a lower sum of five skinfolds (F=18.8, p<0.001) over 12 months.
Activity, fitness, and self-perception: The normal weight group possessed higher levels of self-reported physical activity than did the at risk of overweight children (F=4.1, p<0.05) (Figure 1). Follow-up univariate analyses showed that group differences were significant at zero and three months (p<0.05) only. Normal weight children also exhibited consistently higher levels of aerobic fitness (F=14.3, p<0.001) (Figure 2), and pair-wise comparisons revealed differences at all time points (all p<0.01). While no difference was found in aerobic fitness levels between boys and girls at baseline, a main effect emerged over the course of the study, with boys scoring higher on the 20-MST (F=7.9, p<0.01). Univariate comparisons showed that boys performed better on the 20- MST at three, six, and 12 months (all p<0.05). During the study period, self-perceived social acceptance remained lower among at risk of overweight children in relation to normal weight children (F=7.3, p<0.01). Pair-wise analyses showed that differences were evident at zero- and three-month time points (p<0.05).
Diet: No differences were detected between at risk of overweight and normal weight groups, but boys had a consistently higher intake of total energy (F=10.8, p<0.01), fat (grams) (F=5.0, p<0.05), carbohydrate (grams) (F=8.8, p<0.01), and protein (grams) (F=9.0, p<0.01). A significant time sex interaction emerged with respect to percent intakes of fat (F=3.1, p<0.05) and carbohydrate (F=3.0, p<0.05). Univariate analyses showed that at 12 months only, percent intake of fat was higher for boys and percent intake of carbohydrate was higher for girls (both p<0.05). No differences were detected between groups in intakes of any of the food groups from Canada's Food Guide to Healthy Eating (CFGHE) (27). However, for the entire sample, intakes of grain products and milk products fell within recommended ranges, intakes of vegetables and fruit and meat and alternatives were low, and intakes of other foods were high (Table 4).
DISCUSSION
This study represents one of the few Canadian longitudinal investigations of lifestyle-related behaviours in a sample of at risk of overweight and normal weight six- to ten-year-old boys and girls. In addition to the anticipated group differences in adiposity, we discovered higher baseline self-reported physical activity, aerobic fitness, and self-perceived social acceptance scores in normal weight children; these differences were generally maintained over the long term.
Boys compared with girls
Longitudinal analyses revealed that boys were more aerobically fit and scored lower in self-perceived behavioural conduct. Dietary intakes were similar between the at risk of overweight and normal weight groups, but boys consumed more total energy, which was reflected in their higher absolute intakes of fat, carbohydrate, and protein.
Given the manner in which the at risk of overweight and normal weight groups -were distinguished, consistent anthropometric differences were anticipated. The differences we found between the sexes were also in the expected direction, with girls having higher levels of body fat. This observation is consistent with nationally representative Canada Fitness Survey data (28), which have highlighted a sexual dimorphism in body fatness that becomes more apparent m girls in later childhood.
Activity and fitness levels
Our findings agree with previous observations of lower activity levels among overweight children (7,10). To our knowledge, our study is the first to use the PAQ-C to compare physical activity levels in groups categorized by overweight status. Group differences in PAQ-C scores were considered at all four time points, and yet individual pair-wise comparisons indicated that groups differed at zero and three months only. Because no intervention was delivered, we can only speculate why PAQ-C scores of the at risk of overweight group increased over time in relation to the normal weight group. It is possible that the former group learned to provide more socially desirable responses as the study progressed. Participating m a long- term study of health-related behaviours may have influenced physical activity attitudes and behaviours, and elicited an improvement. Seasonal differences do not appear to explain the one-year (zero to 12 months) change, as both measurement intervals occurred in the fall. Sex differences did not achieve significance, but there was a trend (F=3.4, p=0.07) for boys to be slightly more active over the course of the study. This finding is similar to those from earlier studies, in which boys rated themselves as more physically active on the PAQ-C (29).
Figure 1
Differences in self-reported physical activity between at risk of overweight and normal weight groups over 12 months (based on the Physical Activity Questionnaire for Older Children [PAQ-C])
Figure 2
Differences in aerobic fitness between at risk of overweight and normal weight groups over 12 months (based on the 20-metre shuttle run test [20-MST])
Table 4
Dietary intake (assessed by 24-hour food recall) of absolute servings/day from food groups based on Canada's Food Guide to Healthy Eating (CFGHE) (27)
The observation that at risk of overweight children were consistently less aerobically fit than normal weight children was not unexpected. Despite differing opinions on the best means of expressing fitness data in children (30), a general observation has been that overweight boys and girls possess lower aerobic fitness levels than their non-overweight counterparts (12). Using the 20- MST, Marshall and Bouffard (31) documented lower aerobic fitness levels in obese versus non-obese youth. Our data also were in agreement with previous study findings (32) of sex differences in aerobic fitness (i.e., boys fitter than girls) on the 20-MST. Grade 1 boys from elementary schools offering quality daily physical education (QDPE) were more aerobically fit than were grade 1 girls from QDPE schools, a finding confirming that measurable differences in aerobic fitness exist in young boys vs. gi\rls (31).
Perceptions of being overweight
Social and cultural perceptions of being overweight were already being established in this sample of children. The lower scores on the social acceptance sub-scale for the at risk of overweight group suggested that their greater degree of adiposity had had an impact on their perceived acceptance by others. Our longitudinal observations also revealed a borderline significant effect of self- perceived physical appearance (i.e., a lower self-perception in those at risk of overweight [F=3.9, p=0.05]); this sub-scale is particularly relevant to children with a high BMI. Others have demonstrated that self-perception changes become increasingly evident as children mature. Strauss (33) assessed global self-worth and scholastic competence in obese and non-obese children, and failed to observe any group differences at baseline. However, in follow-up measurements four years later, global self-worth scores decreased in obese boys, obese Hispanic girls, and obese white girls compared with their non-obese peers; no changes in scholastic competence were detected. Others have shown that an increased BMI over one year was associated with a change toward a less favourable self-concept in physical activity and global self-worth domains (34).
Dietary findings
Overall, we did not observe significant diet-related differences with respect to overweight status. Previous reports have suggested that overweight children tend to consume more total energy or fat than do their normal weight peers (6-8). Given the relatively small number of children in the at risk of overweight group (n=20), and the possibility that under-reporting may be substantial in overweight youth (35), we may have been unable to detect measurable nutrition-related differences.
We did observe that boys consumed more total energy, fat, carbohydrate, and protein. This finding was consistent with earlier reports on Canadian (13,36) and American (11) children. Boys had marginally higher levels of self-reported physical activity than girls, and so this higher energy intake may simply have reflected increased demands because of energy expenditure. Despite the differences in absolute and relative intakes, and the significant sex time interaction we observed for fat and carbohydrate intake in boys and girls, the macronutrient composition of the diets of all groups were similar to Canadian recommendations (37). These disparities therefore appear to be of statistical but not clinical significance.
The 24-hour dietary recalls revealed that the entire cohort had intakes of grain products and milk products within the recommended ranges. However, servings of vegetables and fruit and meat and alternatives were lower than those recommended by CFGHE (27). Specific recommendations do not exist for servings from the "other foods" group, but moderate consumption is suggested.
In one of the few studies available for comparison (38), children (n=226) completed 24-hour recalls six times over 12 months. Temporal patterns were not investigated, but intakes of vegetables and fruit were low for both sexes, while meat and alternatives were low m girls only. In both sexes, boys and girls consumed gram products and milk products in adequate amounts, while the consumption of other foods was relatively high and increased with age. More recently (39), the same research group reported marginally low intakes of vegetables and fruit (3.9 1.9 servings/day) and meat and alternatives (1.9 0.7 servings/day) in nine- to 13-year-old children. Intakes of grain products (5.5 1.3 servings/day) were adequate for the group, but intakes of milk products, while adequate for seven- to nine-year-old children (2.7 1.1 servings/day), were inadequate for the ten- to 12-year-old group. Although nationally representative data for Canadian children are lacking, children in the current study appeared to have diets similar to those in other published reports.
SUMMARY
We found significant anthropometric differences in the expected direction between children, according to overweight and sex status. Normal weight children were more physically active and aerobically fit, and scored higher in social acceptance than did their at risk of overweight peers. Boys were generally more active, fitter, and had a higher energy intake than did girls, but these differences did not correspond to disparities in risk of overweight. Macronutrient levels were within recommended ranges for the entire cohort, but dietary quality based on food group servings did not satisfy current guidelines. This research revealed key lifestyle-related behavioural differences between groups according to overweight status and sex; the dramatic rise in childhood overweight within Canada over the past two to three decades requires researchers and health professionals to continue exploring adiposity correlates in youth so that appropriate prevention and treatment can be established.
RELEVANCE TO PRACTICE
While several of the cross-sectional group differences we observed at baseline remained significant over the long term, other group differences (i.e., self-perceived behavioural conduct and aerobic fitness in boys versus girls) emerged once longitudinal measures were collected. These observations highlight the potential limitations of cross-sectional studies and underscore the importance of assessing lifestyle-related behaviours using longitudinal research designs.
These results also revealed that most children's diets do not satisfy CFGHE recommendations. Along with promoting a physically active lifestyle, dietitians should continue to work to develop and implement healthy nutrition education messages for all boys and girls.
Acknowledgements
We gratefully acknowledge the Canadian Fitness and Lifestyle Research Institute and the Children's Health Foundation of Northern Alberta for their financial support, and the children and families for their enthusiastic participation m this study.
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GEOFF D.C. BALL, PhD, RD, Department of Pediatrics and Child Health, University of Alberta, Edmonton, AB;
J. DRU MARSHALL, PhD, Faculty of Physical Education and Recreation, University of Alberta, Edmonton, AB;
LINDA J. MCCARGAR, PhD, RD, Department of Agricultural, Food, and Nutritional Science, Faculty of Agriculture, Forestry, and Home Economics, University of Alberta, Edmonton, AB
Copyright Dietitians of Canada Fall 2005
Source: Canadian Journal of Dietetic Practice and Research
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