Gastric bypass surgery for obesity decreases the reward value of a sweet-fat stimulus as assessed in a progressive ratio task

Background: Obesity is among the leading causes of disease and death. Bariatric surgery is the most effective treatment of obesity. There is increasing evidence that after gastric bypass surgery, patients and animal models show a decreased preference for sweet and fatty foods. The underlying mechanism may include alterations in taste function. Objective: We hypothesize that a gastric bypass reduces the reward value of sweet and fat tastes. Design: In this prospective case-control study, 11 obese patients who were scheduled to undergo a gastric bypass and 11 normal-weight control subjects in the fed state clicked a computer mouse to receive a sweet and fatty candy on a progressive ratio schedule 10 wk apart (in patients, testing took place 2 wk before and 8 wk after gastric bypass surgery). Subjects worked progressively harder to obtain a food reward (reinforcer) until they stopped clicking (ie, the breakpoint), which was a measure of the reinforcer value. Breakpoints were assessed by the number of mouse clicks in the last completed ratio. The experiment was repeated in a different cohort by using vegetable pieces as the reinforcer. Results: Breakpoints in the test sessions of control subjects correlated highly for both reinforcers. The median breakpoint for candies, but not vegetables, was reduced by 50% in the obese group after gastric bypass. Patients with the largest reduction in the breakpoint had the largest decrease in BMI. Conclusions: Gastric bypass surgery resulted in the selective reduction of the reward value of a sweet and fat tastant. This application of the progressive ratio task provided an objective and reliable evaluation of taste-driven motivated behavior for food stimuli after obesity surgery. This trial was registered at clinicaltrials.gov as NCT01531738. Am J Clin Nutr 2012;96:467-73.