A pilot functional MRI study in Roux-en-Y gastric bypass patients to study alteration in taste functions after surgery.

backgroundGastric bypass restricts food intake, with a limited component of malabsorption. Gut and brain hormone changes also facilitate improvements in weight and comorbidities. Patients' perception of taste and smell also change, along with reduced appetite for savory meals. Data on how changes in gastrointestinal physiology affect brain centers of perception and reward are sparse.

methodsWith IRB approval, we recruited 13 patients to undergo pre- and postoperative taste testing and functional MRI (fMRI) in response to sweet and salty solutions. A delivery system to the tongue was used, and patients rated intensity and pleasantness. They then underwent fMRI scanning. Sensory and reward areas of the brain were evaluated for activation. Subjects were then compared to non-obese non-surgical controls with the same taste paradigm and scanning twice, at 1 month apart.

resultsAll subjects experienced significant weight loss at 1 month and at 1 year after surgery. As expected, after surgery brain activation in the reward center of the brain was significantly decreased in response to sweet solutions, but this effect was also seen in non-surgical controls, making this result inconclusive. In contrast, surgical patients had significantly increased activation in the reward center to salty taste compared both to their preoperative scans and to healthy controls.

conclusionsAfter GBS, brain activation in the reward system of obese patients responding to palatable tastes may be significantly changed, and such changes can be detected using fMRI. They do not always correlate with subjective reports of intensity and pleasantness. To verify that such taste-related activation changes are caused specifically by the GBS, taste function of a control group of obese patients should be studied during the same period of time without GBS intervention but with similar weight loss.