A Structured Intentions and Action-Planning Intervention Improves Weight Loss Outcomes in a Group Weight Loss Program

Abstract

Purpose. To assess whether forming general behavioral intentions and implementing intentions through action plans promotes weight loss and is moderated by weight loss goals and self-efficacy. Design. A quasi-experimental study comparing change in body mass index (BMI) for 15 months between a behavioral intentions condition (BIC), an implementation intentions condition (IIC), and a comparison condition (CC). Setting. Ten-week weight loss program delivered in weekly group meetings at community medical centers. Subjects. Six hundred thirty-two attendants at the weight loss program (80% of program attendants participated in the study). Intervention. Weight loss program focused on lifestyle changes, augmented by two experimental conditions (vs. a comparison condition): BIC, intended use of weight loss techniques; IIC, intended use and detailed plans for two techniques. Phone follow-up was conducted 3 and 12 months later. Measures. Main outcome: BMI during the program (computed on the basis of weight and height measured on a mechanical medical scale). Experimental manipulations included exposure to list of techniques (BIC/IIC) and structured planning form (IIC); independent variables were assessed with questionnaires (eating self efficacy, weight loss goal, demographics). Analysis. Linear mixed models estimating changes in BMI and their interactions with the planning interventions, goals, and self-efficacy. Results. Participants in the BIC and IIC lost 40% more weight during the 10-week program than those in the CC (1.10 and 1.11 BMI points compared with. 79; ts < −2.76, ps < .01). Weight loss goals interacted with implementation intentions (t = 2.98, p < .01). Self-efficacy was unrelated to weight loss. No differences were found between conditions at 3 and 12 months after the program. Conclusion. Findings revealed that forming implementation intentions promotes weight loss within a weekly program at a field setting and that its effectiveness depends on initial high goals.