Davison KK, Birch LL. Child and parent characteristics as predictors of change in girls’ body mass index. Int J Obes 2001; 25: 1,834-1,842.
PubMed ID: 11781765
To assess parents’ dietary intake and physical activity in addition to children’s intake and physical activity as predictors of girls’ change in BMI between ages five and seven with the goal to develop a comprehensive and context-based model of girls’ change in BMI.
- Five years of age at start of study
- Living with both biological parents.
- Severe food allergies or chronic medical problems affecting food intake
- Dietary restrictions involving animal products.
- Subjects were recruited for the study using flyers and newspaper advertisements
- In addition, families with age-eligible girls within a five-county radius received letters invited them to participate
- Also received follow-up phone calls.
- Analyses conducted using SAS version 6.12
- Data checked for outliers prior to analysis
- Predictors of girls' change in BMI: Hierarchical regression - order of entry of predictor variables was established to reflect the developmental process leading to accelerated changes in children's BMI and the development of overweight.
- Predictor variables were entered in the following order:
- Background and confound variables (i.e., family income; parent education status; girls' BMI at age five)
- Parents' weight status (i.e., familial risk of overweight; partents' change in BMI)
- Parents' physical activity (i.e., frequency and enjoyment of activity)
- Parents' dietary intake (i.e., total energy and percentage fat intake)
- Girls' physical activity (i.e., relative activity and tendency toward activity)
- Girls' dietary intake (i.e., total energy and percentage fat intake)
- Predictor variables were entered in the following order:
- Familial aggregation of risk factors for overweight:
- Correlations among all indicators of weight status, physical activity and dietary intake at time one (baseline); corrrelations between girls' and parents' change in BMI.
Timing of Measurements
- Time 1: In summer before entry into kindergarten, all variables measured except girls' tendency toward activity
- Time 2: In summer during same period before entry into second grade, measurements included girls', mothers' and fathers' BMI, and girls' tendency toward activity.
Girls’ change in BMI:
- Measured height and weight; difference between age five and seven years
- Overweight defined as BMI of at least 17.2kg per m2 at age five and at least 18kg per m2 at age seven years
- Obese defined as at least 19.3kg per m2 at age five and at least 21kg per m2 at age seven years.
- Girls’ dietary intake: Total energy intake and percent of energy from fat (when girls were five, mother’s provided three, 24-hour recalls of their daughters’ food intake); Analyzed using Nutrition Data Systems (NDS 12A; University of Minnesota)
- Girls’ physical activity:
- Relative activity (time one only): Mothers' response to "How active is your daughter relative to other girls her age?"
- Tendency toward activity (time two only): Girls completed shortened version of the Children’s Physical Activity Scale (CPA) (Cronbach's alpha for this sample=0.58)
- Parents’ change in BMI: Measured height and weight
- Parents’ dietary intake: Total energy intake and percent of energy from fat; Semi-quantitative food frequency questionnaire (Kristal)
- Parents’ (mothers' and fathers') physical activity:
- Relative activity: "How many days a week do you exercise or participate in sports?" (Low, Medium, High)
- Enjoyment of activity: "I exercise or play sports for fun." (really describes me; sort of describes me; does not describe me)
- Familial risk of overweight: Value for familial risk of overweight is 1=neither parent overweight, 2=one parent, 3=both parents).
Variables controlled for:
- Girls’ and parents’ total energy intake was adjusted for body weight
- Family income
- Parent education status
- Girls’ BMI at age five years.
- Initial N: 197 girls and their families; N=185 for analysis after outliers removed
- Final N: 168 (only those with complete anthropometric data at both time points)
- Age: Girls: 5.4±0.4 years; Parents: Mothers: 35.4±4.7 years; Fathers: 37.4±5.4 years
- Ethnicity: Non-Hispanic white
- Well-educated (Two-thirds had at least high school)
- Equal proportions with annual incomes greater than $35,000; between $35,000 and $50,000 and over $50,000
- Anthropometrics: See results section
- Location: Central Pennsylvania.
Weight Status, Physical Activity and Dietary Intake
|Time 1||Time 2|
Mean change in BMI
Mean change in BMI
Mean change in BMI
NOTE: At Time 1, girls were 5 years old; At Time 2, girls were 7 years old.
- Girls' mean BMI at ages five and seven years and girls' change in BMI reflect population-level patterns for white five- and seven-year old girls
- Strong degree of tracking was noted in girls' BMI from ages five to seven years (r=0.87, P<0.001)
- Girls' change in BMI was correlated with BMI at age five (r=0.36, P<0.001) and BMI at age seven years (r=0.76, P<0.001)
- 80% of girls who were overweight at age five were also overweight at age seven years
- Only 9% of girls became overweight between ages five and seven years
- Approximately half of mothers were overweight (BMI at least 25kg per m2), reflecting population estimates among women; three-quarters of fathers were overweight, slightly higher than population estimates for men
- Girls' and mothers' reports of girls' activity indicated that girls were moderately active. Parents' reports of their own activity indicated that mothers exercised one to three days per week, whereas fathers tended not to exercise.
- Both mothers and fathers reported an average likeing for physical activity
- Mean energy intake (not controlling for body weight): Girls 1,517 + 311kcal; Mothers 1,807 + 685kcal; Fathers 2,058 + 670kcal
- Mean percentage energy from fat: Girls 31%; Mothers and fathers 36%.
Predictors of Girls' Change in BMI from Age Five to Seven Years
The final model was significant (P<0.0001) and explained 26% of the variance in girls’ change in BMI (r2=0.26).
Girls with greater increases in BMI between ages five and seven years had a higher BMI at age five years (P<0.0001 at entry into model); explained 15% of variance. Other variables explained a further 11% of variance:
- Higher family risk of overweight (P=0.005 at entry into model)
- Higher change in mothers' BMI (P=0.05 at entry)
- Fathers who enjoyed activity less (P=0.01 at entry)
- Fathers with higher energy intake, controlling for body weight (P=0.09 at entry)
- A higher percent energy from fat at age five years (P<0.01 at entry).
Girls’ energy intake at age five (controlling for body weight) was not significantly associated with girls’ change in BMI between age five and seven years (P<0.70).
Analysis of data for those families for which there was complete data for all variables (N=142) did not show meaningful changes in results.
Familial Aggregation of RiskFactors for Overweight
Over 25% of correlations calculated were significant, illustrating the extent to which risk factors for overweight cluster within families (* P<0.05; ** P<0.01).
Significant associations between girls' and parents' weight status:
- Girls BMI and family risk overweight (r=0.19**); Moms' BMI (r=0.14**); Dads' BMI (r=0.21**)
- Moms' BMI and family risk overweight (r=0.65**); Dads' BMI (r=0.22**)
- Dads' BMI and family risk overweight (r=0.21**)
Significant physical activity associations:
- Moms' and dads' frequency of activity were positively correlated (r=0.18*)
- Mom's frequency of activity negatively correlated with moms' BMI (r= -0.15*) and girls' tendency toward activity (r= 0.16*)
- Moms' enjoyment of activity negatively correlated with family risk overweight (r= -0.16*)
- Dads' frequency of activity negatively correlated with dads' BMI (r= -0.18**)
- Dads' enjoyment of activity positively correlated with dads' frequency of activity (r= 0.38**).
Significant dietary intake associations:
- Girls' energy intake not associated with any weight status or physical activity variable.
- Girls' energy intake positively assocciated with moms' energy intake (r=0.19**); Dads' energy intake (r=0.16*)
- Girls' percentage fat intake positively associated with moms' percentage fat intake (r= 0.22**); and negatively associated with moms' frequency of activity (r= -0.20**)
- Moms' energy intake positively associated with moms' enjoyment of activity (r= 0.24**) and moms' percentage fat intake (r=0.22**)
- Moms' percentage fat intake positively associated with moms' BMI (r=0.19**) and negatively associated with moms' enjoyment of activity (r= -0.20**) and moms' frequency of activity (r= - 0.21**); Dads' frequency of activity (r=-0.18**)
- Dads' energy intake positively associated with moms' energy intake (r=0.19**)
- Dads' percentage fat intake positively associated with dads' BMI (r=0.20**); Dads' energy intake (r= 0.41**); and negatively associated with dads' frequency of activity (r= -0.26**) ; Dads' enjoyiment of activity (r= -0.16*).
Partial correlations calculated between girls and parents' change in BMI, controlling for girls' and parents' BMI when girls were five years:
- Mothers' and fathers' change in BMI were positively correlated (r=0.20, PM<0.01) and girls' change in BMI was positively and marginally correlated with mothers' (r=0.14, P<0.10), but not fathers' BMI.
Use of food frequency for parents' dietary intake and use of one question for physical activity assessment are less reliable measures that might obscure some potential associations.
Research Design and Implementation Criteria Checklist: Primary Research
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|3.||Is the focus of the intervention or procedure (independent variable) or topic of study a common issue of concern to nutrition or dietetics practice?|
|4.||Is the intervention or procedure feasible? (NA for some epidemiological studies)|
|1.||Was the research question clearly stated?|
|1.1.||Was (were) the specific intervention(s) or procedure(s) [independent variable(s)] identified?|
|1.2.||Was (were) the outcome(s) [dependent variable(s)] clearly indicated?|
|1.3.||Were the target population and setting specified?|
|2.||Was the selection of study subjects/patients free from bias?|
|2.1.||Were inclusion/exclusion criteria specified (e.g., risk, point in disease progression, diagnostic or prognosis criteria), and with sufficient detail and without omitting criteria critical to the study?|
|2.2.||Were criteria applied equally to all study groups?|
|2.3.||Were health, demographics, and other characteristics of subjects described?|
|2.4.||Were the subjects/patients a representative sample of the relevant population?|
|3.||Were study groups comparable?|
|3.1.||Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT)|
|3.2.||Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline?|
|3.3.||Were concurrent controls used? (Concurrent preferred over historical controls.)|
|3.4.||If cohort study or cross-sectional study, were groups comparable on important confounding factors and/or were preexisting differences accounted for by using appropriate adjustments in statistical analysis?|
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|6.6.||Were extra or unplanned treatments described?|
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