Postingestive processes, which refer to the physiological and behavioural responses occurring after food intake, are crucial for regulating eating behaviour, influencing both the sensation of satiety and food preferences. The research team led by Albino Oliveira Maia investigated the impact of these processes on three distinct groups: healthy individuals, people with obesity, and post-bariatric surgery patients. Specifically, the study explored whether these effects occur through implicit (non-conscious) mechanisms and how the availability of dopamine D2 receptors in the brain is related to these processes. Using the flavour-nutrient conditioning (FNC) method, where the flavour of yogurt enriched with maltodextrin was associated with increased caloric content, it was observed that food preferences were influenced primarily through implicit consumption decisions rather than explicit assessments of flavour pleasantness ratings. In other words, the study demonstrated that FNC affected food choices without participants being consciously aware that they were preferring foods due to their association with nutritional value. This shift was observed in healthy individuals, people with obesity, and post-bariatric patients. Furthermore, people with obesity showed lower availability of dopamine D2 receptors, crucial in the brain's reward system. After bariatric surgery, particularly gastric bypass, there was an increase in receptor availability, which may be linked to improved feeding behavior regulation. These findings suggest that changes in the reward system may play a role in the surgery's effectiveness in reducing weight and modifying eating behaviours. This study was supported by the BIAL Foundation, in the scope of the research project 176/10 - Dopaminergic regulation of dietary learning in humans and rodents, and published in the journal PLOS BIOLOGY, in the article Postingestive reward acts through behavioral reinforcement and is conserved in obesity and after bariatric surgery.
ABSTRACT
Postingestive nutrient stimulation conditions food preferences through striatal dopamine and may be associated with blunted brain responses in obesity. In a cross-sectional study, we tested flavor-nutrient conditioning (FNC) with maltodextrin-enriched yogurt, with maltodextrin previously optimized for concentration and dextrose equivalents (n = 57), and to mask texture cues (n = 102). After conditioning, healthy volunteers (n = 52) increased preference for maltodextrin-paired (+102 kcal, CS+), relative to control (+1.8 kcal, CS-) flavors, as assessed according to intake, but not pleasantness. In a clinical study (n = 61), behavioral conditioning without effects on pleasantness was confirmed across pre-bariatric candidates with obesity, weight-stable post-surgery patients, and healthy controls, without significant differences between groups. Striatal dopamine D2-like receptor (DD2lR) availability, assessed with [123I] IBZM SPECT, was reduced in the obesity group and strongly correlated with conditioning strength and a measure of restrained eating in patients with gastric bypass. These results show that postingestive nutrient stimulation influences human food choices through behavioral reinforcement and is conserved in obesity and after bariatric surgery.
