Life Events, Physical Activity, and Weight Loss Maintenance: Decomposing Mediating and Moderating Effects of Health Behavior.

Background: This analysis helps clarify the individual and joint effects of moderate to vigorous physical activity (MVPA) in concert with significant life events (eg, divorce, marriage, job change or loss, pregnancy, etc) on weight following a behavioral weight loss intervention.

Methods: Data from the Tracking Study weight loss trial were utilized to perform a 4-way decomposition of moderation and mediation of life events (≥ 1 vs 0) and MVPA (low <2500 kcal vs high ≥ 2500 kcal) on 24-month weight.

Results: The total effect of life events and MVPA on weight was estimated to be 1.63 kg (95% confidence interval = 0.30 to 2.96; P = .02). The controlled direct effect of life events on 24-month weight suggested that experiencing at least one life event controlling for MVPA was associated with an increase of 2.31 kg (95% confidence interval = 0.29 to 4.33) at 24 months. Other interaction and mediation estimates were not statistically significant.

Conclusions: This analysis offers new potential for examining health behaviors that may act as both mediators and effect modifiers of health. Although more work is needed to understand the interaction of life events and MVPA on weight loss maintenance, findings help rule out mediation. Life events and MVPA should be considered for their unique effects on weight loss maintenance in the future.