Physical activity planning interventions, body fat and energy-dense food intake in dyads: ripple, spillover, or compensatory effects?

Objectives: It is unclear if planning to change one behavior may prompt changes in other health behaviors or health outcomes. This study tested if physical activity (PA) planning interventions may result in (i) a body fat reduction in target persons and their dyadic partners (a ripple effect), (ii) a decrease in energy-dense food intake (a spillover effect), or an increase in energy-dense food intake (a compensatory effect). Method: N = 320 adult-adult dyads were assigned to an individual (‘I-for-me’), dyadic (‘we-for-me’), or collaborative (‘we-for-us’) PA planning intervention or a control condition. Body fat and energy-dense food intake were measured at baseline and at the 36-week follow-up. Results: No Time x Condition effects were found for target persons’ body fat. There was a reduction in body fat among partners participating in any PA planning intervention, compared to the control condition. Across conditions, target persons and partners reduced energy-dense food intake over time. The reduction was smaller among target persons assigned to the individual PA planning condition compared to the control condition. Conclusions: PA planning interventions delivered to dyads may result in a ripple effect involving body fat reduction among partners. Among target persons, the individual PA planning may activate compensatory changes in energy-dense food intake.