The increasing prevalence of obesity in children and youth is largely attributed to unfavorable changes in diet, physical activity, and sedentary behaviors.1-4
The Institute of Medicine calls for multiple strategies to change these behaviors in young people5
and other groups such as the US Department of Health and Human Services6
call for changes in the same behaviors to prevent several chronic diseases. Because most adolescents fail to meet recommendations for multiple health behaviors7
interventions targeting multiple behaviors are attractive. However changing multiple behaviors simultaneously is difficult8
and if diet, physical activity, and sedentary behavior covary over time, this could impact both the intended and unintended consequences of interventions meant to improve these behaviors.
Covariation has also been termed “clustering of health behaviors” and defined as assocations between two or more health behaviors.”9
Defining covariation in this manner does not make a distinction between measuring the behaviors cross-sectionally versus prospectively. In the present study, we examine prospective covariation, which is conceptually more relevant for informing the design of interventions. Though numerous, cross-sectional studies on the clustering of behaviors have limited implications for interventions because they provide no information about temporal change. Prospective studies can determine whether, over time, two or more behaviors are independent or tend to change in tandem. Interventions to prevent and treat obesity and chronic diseases in youth often target multiple behaviors, specifically, diet, physical activity, and sedentary behaviors. There is the possibility that these behaviors are related to one another such that improvements in one or two result in worsening of the other. If this is the case, trying to improve some behaviors can have deleterious effects on attempts to improve the others, leading to unintended consequences. Conversely, if the behaviors tend to covary in a positive way, improving together, this might suggest more efficient ways to target improvements in multiple behaviors.
If covariation occurs over time among behaviors, it could occur for several reasons. One is that the behaviors could be inherently related. For example, decreasing TV viewing reduces exposure to commercials for unhealthy foods and allows more time for other activities. Another mechanism might be that some behaviors help explain part or all of the relationships between other behaviors. An example of this might be parent modeling or use of behavior change skills such as goal-setting. Perhaps adolescents readily generalize behavior change strategies across multiple behaviors resulting in change for more than one behavior.
Physical activity and dietary behaviors are thought to be related for several reasons. Studies suggest that exercise reduces hunger and delays eating.10
However, there are mixed results. Exercise may also change the tastes of foods. Studies have shown increases or no change in the palatability of food during or after bouts of exercise and none have shown decreases in palatability.10
Another suggestion is that more active individuals are motivated to eat healthier diets.10
Conversely, active individuals may justify eating unhealthy foods due to their higher activity levels.
Relationships between diet and physical activity have been demonstrated in cross-sectional studies in adults11-16
and youth9, 17-21
but there is less known about the covariation of these behaviors over time.22
One study examined cross-sectional relationships between healthy eating behaviors and physical activity over 7 years, from 6th
grades some of whom were part of a health behavior intervention.9
Results showed that those who had the healthiest food habits were more active than those in the lowest quintile of healthy food habits. The largest differences were after 9th
grade and for those in the intervention condition. A systematic review concluded cross-sectional evidence existed for the association between physical activity and healthy diet for children but not adolescents.23
A recent cross-sectional study of 8-10 year old African-American girls found physical activity was negatively associated with fat intake and positively associated with carbohydrate intake.24
However, the same study did not find covariation between diet and nutrition behaviors over 12 weeks.25
Additional cross-sectional studies have examined the associations between sedentary behavior and nutrition and/or physical activity in youth. In a large sample of U.S. high school students, TV viewing was associated with less consumption of fruits and vegetables.26
A meta-analysis showed small effect sizes for the relationship between TV viewing and physical activity in children and adolescents.2
Epstein has shown experimentally that reducing sedentary behaviors can increase physical activity, but effects were inconsistent across studies and, in some cases, depended on weight status of the participants. When sedentary time was reduced, obese youth decreased in PA while non-obese youth increased.27-29
The purpose of the present study was to examine whether and how diet, sedentary, and physical activity behaviors covary over time in a sample of adolescents enrolled in a behavior change intervention study over a one-year period. Because of the paucity of literature examining covariation over time, we did not have specific hypotheses about how covariation might occur or in what direction.