OBJECTIVE To examine the psychological process of lifestyle change among adults at risk for type 2 diabetes.

RESEARCH DESIGN AND METHODS A randomized control trial in which 307 volunteers (intervention, n = 208; wait control, n = 99) diagnosed with prediabetes completed a six-session group-based intervention to promote healthier living. Participants’ motivation to change, diet and exercise self-efficacy, mood, knowledge about diabetes, activity levels, healthy eating, waist circumference, and weight were assessed before and after the program.

RESULTS Participation in the program was associated with significant increases in healthy eating and physical activity, reductions in waist and weight, and improvements in motivation, positive mood, self-efficacy, and knowledge. Examination of the pathways to lifestyle change showed that the educational aspect of the program increased activity levels because it increased diabetes knowledge and improved mood. Eating behavior was not mediated by any of the psychological variables. Improvements in diet and physical activity were, in turn, directly associated with changes in weight and waist circumference.

CONCLUSIONS Although the program significantly improved motivation, self-efficacy, and mood, its impact on knowledge uniquely explained the increase in physical activity. Group-based programs that are tailored to lifestyle behaviors may provide a cost-effective method of diabetes prevention, but more research is needed to explain why they improve healthy eating.