Roux-en-Y gastric bypass surgery changes food reward in rats

CONTEXT: Roux-en-Y gastric bypass surgery (RYGB) is currently the most effective treatment for morbid obesity and clinical studies suggest that RYGB patients change food preferences and the desire to eat. OBJECTIVE: To examine hedonic reactions to palatable foods and food choice behavior in an established rat model of Roux-en-Y gastric bypass surgery (RYGB). METHODS AND DESIGN: Male Sprague-Dawley rats and selected line obesity-prone rats that were rendered obese on a high-fat diet underwent RYGB or sham surgery and were tested for ‘liking’ and ‘wanting’ of palatable foods at different caloric densities 4 – 6 months after surgery. RESULTS: Compared with sham-operated (obese) and age-matched lean control rats, RYGB rats of both models exhibited more positive orofacial responses to low concentrations of sucrose but fewer to high concentrations. These changes in ‘liking’ by RYGB rats were translated into a shift of the concentration-response curve in the brief access test, with more vigorous licking of low concentrations of sucrose and corn oil, but less licking of the highest concentrations. The changes in hedonic evaluation also resulted in lower long-term preference/acceptance of high-fat diets compared with sham-operated (obese) rats. Furthermore, the reduced ‘wanting’ of a palatable reward in the incentive runway seen in sham-operated obese SD rats was fully restored after RYGB to the level found in lean control rats. CONCLUSIONS: The results suggest that RYGB leads to a shift in hedonic evaluation, favoring low over high calorie foods and restores obesity-induced alterations in ‘liking’ and ‘wanting’. It remains to be determined whether these effects are simply due to weight loss or specific changes in gut-brain communication. Given the emerging evidence for modulation of cortico-limbic brain structures involved in reward mechanisms by gut hormones, RYGB-induced changes in the secretion of these hormones could potentially be mediating these effects.