Postingestive reinforcement is conserved in obesity and after bariatric surgery.

Postingestive reward contributes to acquisition of food preferences, mediated by striatal dopamine, with assessment in humans, while challenging, suggesting blunted brain responses to postingestive nutrient stimulation in obesity. To perform postingestive conditioning in humans, we used carboxymethylcellulose, a food thickener, to optimize conditions where maltodextrin, an insipid carbohydrate, was not detectable by sensory cues (n=159). In the resulting Flavour Nutrient Conditioning protocol using flavoured yoghurts, where one flavour was paired with maltodextrin (+102 Kcal, CS+) and another with carboxymethylcellulose (+1.8 Kcal, CS-), we found that in healthy volunteers (n=52), preference for CS+ increased after conditioning, when assessed according to intake, with no effects on pleasantness scores. This protocol and [123I] IBZM SPECT, to assess availability of striatal dopamine D2-like receptors (DD2lR) were applied in a clinical study (n=61) with pre-bariatric candidates with obesity, weight-stable patients after surgery, and an additional group of healthy controls. Conditioning was conserved among participants in the clinical study, and did not differ significantly between the 3 groups. However, striatal DD2lR availability was reduced in patients from the obesity group, when compared both to healthy volunteers and the surgical group. Importantly, in exploratory analyses, DD2lR availability was strongly correlated with conditioning strength, as well as a measure of restrained eating, but only in patients with gastric bypass. These results suggest that postingestive reinforcement, while conserved in obesity and after bariatric surgery, may be associated to post-surgery recovery of central dopaminergic homeostasis and to changes in feeding behaviour after gastric bypass.