Opioids as facilitators of feeding: can any food be rewarding?

Palatability is one of the most rewarding aspects of consummatory behavior. Opioids, potent facilitators of intake of sweet and fat tastants, are thought to mediate hedonics of feeding. However, the rewarding context of consumption is not limited to palatability, and gratification can be achieved through other means, e.g., eating to satisfy hunger. The current review discusses the role of opioid peptides in food intake regulation by incorporating this expanded concept of feeding reward. We present evidence that, aside from increasing sugar/fat consumption, opioids propel the intake of diets whose gustatory value is low but are nonetheless consumed under circumstances allowing feeding gratification to occur. Opioids enhance reward-driven consumption by acting within the classical reward circuitry and also by signaling reward at sites that regulate other aspects of food intake, such as satiety and aversion. We conclude that, due to the complexity of neural and functional interactions, opioids are capable of enhancing pleasure of eating any food--palatable, bland or even aversive--making any meal into a more rewarding experience, despite possible consequences.