Effects of manipulating sedentary behavior on physical activity and food intake

Objectives: Sedentary behaviors have been correlated with obesity. We investigated whether changes in sedentary behaviors relate to changes in energy intake and/or physical activity. Study design: Experimental within-subject crossover design in which children participated in three 3-week phases: baseline and increased and decreased targeted sedentary behaviors. Participants: Thirteen 8- to 12-year-old, nonobese children. Measurements: Sedentary behaviors were measured through the use of daily activity logs, physical activity measured with accelerometers, and energy intake measured by means of repeated 24-hour recalls collected during each phase. Energy intake, energy expenditure, and energy balance per day were calculated. Results: Children showed significant ( P < .001) increases of 50% and decreases of 53% in targeted sedentary behaviors from baseline during the increase and decrease phases, respectively. There was a significant ( P = .05) increase in energy balance per day (+350.7 kcal) when sedentary behaviors were increased, as the result of an increase in energy intake per day (+250.9 kcal) and a decrease in energy expenditure (−99.8 kcal). No significant changes in energy balance were observed when sedentary behaviors were decreased. Conclusions: Increasing sedentary behaviors had a greater influence on physical activity and energy intake than reducing sedentary behavior in nonobese youth. In some children, changes in sedentary behaviors may be important to modify energy balance and prevent obesity. (J Pediatr 2002;140:334-9)