This research is a randomized controlled trial to compare long-term outcomes behavioral weight loss interventions that include either low-fat or low-glycemic load dietary instruction. Targets for energy intake and expenditure, and behavioral skills taught, are identical across the two diets. Additionally, both treatments include 20 weekly group sessions, followed by 10 every-other-week sessions. Participants are overweight and obese adults with type 2 diabetes. The primary outcomes are changes in weight and glycated hemoglobin. Those randomized to the low-glycemic load diet are expected to achieve greater weight losses and maintain better glycemic control at the end of treatment (i.e., week 40) and after 1 year of no-treatment follow-up (i.e., week 92).