Processes of behavior change and weight loss in a theory-based weight loss intervention program: a test of the process model for lifestyle behavior change
International Journal of Behavioral Nutrition and Physical Activity
© 2015 Gillison et al.; licensee BioMed Central. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
BackgroundProcess evaluation is important for improving theories of behavior change and behavioral intervention methods. The present study reports on the process outcomes of a pilot test of the theoretical model (the Process Model for Lifestyle Behavior Change; PMLBC) underpinning an evidence-informed, theory-driven, group-based intervention designed to promote healthy eating and physical activity for people with high cardiovascular risk.Methods108 people at high risk of diabetes or heart disease were randomized to a group-based weight management intervention targeting diet and physical activity, or to usual care. The intervention comprised nine group based sessions designed to promote motivation, social support, self-regulation and understanding of the behavior change process. Weight loss, diet, physical activity and theoretically defined mediators of change were measured pre-intervention, and after four and 12?months.ResultsThe intervention resulted in significant improvements in fiber intake (M between-group difference?=?5.7?g/day, p?<?.001) but not fat consumption (?2.3?g/day, p?=?0.13), that were predictive of weight loss at both four months (M between-group difference?=??1.98?kg, p?<?.01; R2?=?0.2, p?<?0.005), and 12?months (M difference?=??1.85?kg, p?=?0.1; R2?=?0.1, p?<?0.01). The intervention was successful in improving the majority of specified mediators of behavior change, and the predicted mechanisms of change specified in the PMBLC were largely supported. Improvements in self-efficacy and understanding of the behavior change process were associated with engagement in coping planning and self-monitoring activities, and successful dietary change at four and 12?months. While participants reported improvements in motivational and social support variables, there was no effect of these, or of the intervention overall, on physical activity.ConclusionsThe data broadly support the theoretical model for supporting some dietary changes, but not for physical activity. Systematic intervention design allowed us to identify where improvements to the intervention may be implemented to promote change in all proposed mediators. More work is needed to explore effective mechanisms within interventions to promote physical activity behavior.
This is a freely-available open access publication. Please cite the published version which is available via the DOI link in this record.
International Journal of Behavioral Nutrition and Physical Activity, 2015, Vol. 12, pp. 1 - 15