Planning to lose weight: Randomized controlled trial of an implementation intention prompt to enhance weight reduction among overweight and obese women.

OBJECTIVE: The trial investigates the effects of augmenting an established weight-reduction intervention with implementation intention prompts. DESIGN: Fifty-five overweight or obese women (ages 18 to 76 years; body mass index from 25.28 to 48.33) enrolled in a commercial weight reduction program were randomly assigned to either an implementation intention prompt or a control condition. Data were collected twice, with a time gap of 2 months. MAIN OUTCOME MEASURES: The primary outcome was participants' change in weight and body mass index from preintervention to follow-up. RESULTS: Repeated measures analysis of variance revealed a significant Time = Condition interaction: On average, implementation intention prompt participants lost 4.2 kg (95% confidence interval = 3.19, 5.07), whereas control participants lost 2.1 kg (95% confidence interval = 1.11, 3.09). The change in frequency of planning mediated the effects of the intervention on weight and body mass index change. CONCLUSION: Among obese or overweight women participating in a commercial weight loss program, those who learn to form implementation intentions can achieve greater weight reduction. Planning facilitation is a key mechanism explaining enhanced weight loss generated by implementation intention formation.