Objective:  Meta-analyses of behavior change (BC) interventions typically find large heterogeneity in effectiveness and small effects. This study aimed to assess the effectiveness of active BC interventions designed to promote physical activity and healthy eating and investigate whether theoretically specified BC techniques improve outcome. Design:  Interventions, evaluated in experimental or quasi-experimental studies, using behavioral and/or cognitive techniques to increase physical activity and healthy eating in adults, were systematically reviewed. Intervention content was reliably classified into 26 BC techniques and the effects of individual techniques, and of a theoretically derived combination of self-regulation techniques, were assessed using meta-regression. Main Outcome Measures:  Valid outcomes of physical activity and healthy eating. Results:  The 122 evaluations (N = 44,747) produced an overall pooled effect size of 0.31 (95% confidence interval = 0.26 to 0.36, I²  = 69%). The technique, “self-monitoring,” explained the greatest amount of among-study heterogeneity (13%). Interventions that combined self-monitoring with at least one other technique derived from control theory were significantly more effective than the other interventions (0.42 vs. 0.26). Conclusion:  Classifying interventions according to component techniques and theoretically derived technique combinations and conducting meta-regression enabled identification of effective components of interventions designed to increase physical activity and healthy eating.

Interventions designed to change health-related behaviors generally include many components and typically produce small effects in meta-analyses, but with large heterogeneity in effectiveness (e.g., Dishman & Buckworth, 1996; Grimshaw et al., 2004; National Institute for Health & Clinical Excellence, 2007). This limits the potential for understanding how intervention content relates to effectiveness and, consequently, the inferences that can be drawn regarding optimal design and the content of future behavior change interventions. Recent guidance has called for new methods to evaluate the effects of “complex” interventions (Craig et al., 2008). This study aimed to assess the utility of classifying the content of behavior...