Roux-en-Y Gastric Bypass Reduces Preprandial Appetite and Energy Intake Without Altering Relative Macronutrient Intake

Obesity is a chronic and relapsing disease with significant health risks. Roux-en-Y Gastric Bypass (RYGB) is an effective treatment, but its impact on the macronutrient composition of energy intake and postoperative appetite remains poorly understood. In this multi-centre, prospective observational study, we conducted a four-choice drinkometer test to directly measure energy intake from four stimuli differing in their caloric density and macronutrient composition in 23 adult females before and 1, 3, 6, and 12 months after RYGB and compared to females with obesity (n=24) and normal weight (n=11). We found that RYGB significantly reduced total energy intake by 60% within the first year after surgery, without altering the relative macronutrient intake. Appetite assessments indicated reduced preprandial appetite after surgery, which together with the reduced absolute energy intake resulted in balanced satiation quotients. These findings suggest that RYGB primarily reduces meal size through appetite regulation rather than altering dietary preferences.