The present study provided unique prospective data to examine longitudinal associations between energy balance behaviors and weight change among a community sample of adults and adolescents recruited from the same HH. No previous studies have prospectively examined behavior changes related to weight gain among related adults and adolescents living in the same HH. Despite low power for these secondary analyses, a clear association was observed among adolescents between reduction in TV hours and decreased weight gain over one year. These findings are important, as they have direct implications for clinical recommendations to parents. Reducing TV hours is a clear strategy parents can use to help prevent excess weight gain among their children.
The present study was also unique in its ability to directly compare adults (parents) and adolescents (their children) living in the same HHs. It is clear that the effects of TV hours are different for parents and children. TV was not predictive of excess weight gain over the one-year observation period among the adults.
Although the reasons for this observed difference are not clear, the finding highlights the potential differences by age in strategies that might be effective in preventing excess weight gain and obesity, even among people in the same HH. An advantage of reducing TV hours among adolescents as an obesity-prevention strategy is that parents in the HH control the household policy around TV viewing hours and other HH TV-related practices such as whether the children are allowed to have TVs in their bedroom. The presence of a TV in a child’s bedroom is associated with as much as three times the amount of TV viewing compared to children without TVs in the bedroom.2,3
Several mechanisms could promote weight gain as a consequence of TV viewing. TV viewing is positively associated with energy intake and high fat food consumption among adults and adolescents.9,13,32,52,53
The association is thought to be due in part to the fact that TV exposes people to a high volume of food advertising and many people eat while watching TV, which may result in eating more frequently, eating larger quantities of food or food of lower nutritional quality.54
Energy intake and eating locations were not measured in the present study.
PA is a second mechanism through which TV could affect body weight change. Significant inverse associations between TV viewing and PA among youth have been reported in several studies.4,5,9,14,15
By contrast, the results of two school-based TV reduction intervention studies found no significant effects on youth PA levels.16,20
It is hypothesized by some that leisure time PA and time spent in sedentary entertainment may be independent.11,13,16,20,
In the present study, PA was not associated with BMI z-score in adolescents, cross-sectionally or prospectively.
The present study was unique in its inclusion of a community-based sample of 90 HHs with a range of education and income, and in its inclusion of both adolescents and adults. The prospective study design was a strength, and the retention rate (96%) at one year was high. Behavioral measures used were reliable and valid, and BMI z-scores and BMI were computed from directly measured weight and height. In the main intervention, HH TV viewing weekly hours were reduced by about 50% using an objective TV viewing limiting device among the intervention HHs.42
Limitations of the present study included the self-selected sample and the limited power to detect associations between changes in energy balance behaviors and BMI. Families self-selected to participate because they initially were motivated to make changes in the HH related to TV viewing time, eating habits and PA. A minimum amount of TV viewing hours had to be met to enroll in the study. However, the enrolled HHs may have had more healthful eating habits than the general population, and no minimum inclusion criteria for fast food or SSB intake were stipulated. For example, the baseline consumption of SSBs and frequency of eating out was lower than national estimates.29,30,55,56
This may have limited the ability of the intervention to further change these HH behaviors and as a result, limited the ability to detect associations between changes in these behaviors and changes in BMI. The relatively brief duration of follow-up is another limitation. A longer follow-up period may have enabled the small, cumulative behavioral effects on body weight to be detected. Although reliable and valid PA measures were used, the adolescent measure was self-administered instead of administered by an interviewer, which is the usual method of administration. This may have resulted in higher than usual measurement error. Finally, the dietary questionnaire was limited to a short list of targeted foods and beverages. The limitations of food frequency questionnaires are well-understood.57