Effects of obesity surgery on food preferences, taste and reward in animals and humans

Abstract

BACKGROUND: After Roux-en-Y gastric bypass bariatric surgery (RYGB) patients and animal models show a decreased preference for sweet/fatty foods. However, there are significant discrepancies in the findings of animal and human studies, and the mechanisms are not understood. AIMS: To investigate: 1. The effect of a high-fat (HFD) vs. low-fat (LFD) pre-operative maintenance diet on the ingestive behaviour of rats after RYGB 2. The effects of RYGB vs. gastric banding (BAND) surgery on food hedonics and brain reward systems in humans 3. The effects of RYGB on taste in humans METHODS: Study 1: Rats were fed either LFD or HFD before RYGB or sham surgery. Ingestive behaviour was assessed after surgery using food preference tests. Study 2: Brain reward responses to food were investigated using functional magnetic resonance imaging (fMRI), eating behaviour and metabolic phenotyping in body mass index (BMI) matched un-operated controls and patients after RYGB and BAND surgery. Study 3: The intensity and reward of sweet, fat and fat/sweet taste stimuli were assessed in patients undergoing RYGB using behavioural techniques. RESULTS: Study 1: Pre-operative maintenance diets with different fat contents, did not affect post-surgical weight loss or caloric intake. HFD-RYGB rats exhibited behaviour consistent with condition taste aversion to a familiar stimulus, compared to condition taste aversion to a novel stimulus in the LFD-RYGB rats. Study 2: Patients after RYGB had lower activation in brain reward systems to food and lower food hedonics than BAND patients and/or BMI-matched unoperated controls. Anorexigenic plasma gut hormones, plasma bile acids and dumping syndrome scores were higher in RYGB patients. Study 3: RYGB increased the intensity of fat/sweet taste solutions and reduced the reward value of fat/sweet stimuli. CONCLUSION: Pre-operative feeding may affect ingestive behaviour after RYGB. The mechanisms underlying the healthier food preferences after RYGB include the reduced reward value, and increased aversion to, high-calorie food and taste. Potential mediators are gut hormones, bile acids and altered gut nutrient sensing.