The Diabetes Prevention Program (DPP) is highly effective in promoting weight loss in overweight and obese individuals (e.g., 7% average loss of body weight), and thereby reducing the risk of developing weight-related health consequences. One-on-one DPP sessions, however, are costly and the group-delivered DPP version, the Group Lifestyle Balance program (GLB), is less effective (4% average loss of body weight). The aim of this two-arm parallel randomized controlled trial is to increase the effectiveness of the GLB by integrating habit formation techniques, namely if-then plans and their mental practice, into the program. The study will provide evidence-based data on the effectiveness of an enhanced GLB intervention in promoting weight loss and in reducing weight-related risk factors for chronic health problems.