A growing proportion of the world’s population is affected by obesity. Bariatric (weight-reducing) surgery is a recognized treatment option to achieve sustainable weight reduction. The altered structure of the stomach and intestines leads to numerous changes in hormone balance and metabolism. This particularly affects the communication between the stomach, the intestine and the brain, with possible effects on eating behavior and food preferences. Furthermore, new gut hormone-based (e.g. GLP1-receptor, GLP-1RA) pharmacotherapies which mimic the effect of bariatric surgery show impressive efficacy on weight reduction by modulation of food behavior. The BrainFood2 project uses food purchase data and self-reported food intake to investigate how eating behavior and food preferences change after initiation of anti-obesity treatment. The findings will be used to better understand the regulation of eating behavior in obesity and to derive new approaches for prevention and treatment.