Opioids in the regulation of food intake and energy expenditure.

This paper and the following four papers summarize a symposium on the role of opioids in regulation of feeding, body weight, and energy expenditure. The central sites of opioid action are discussed, as is opioid activity in invertebrates, large animals, and humans. This paper provides a historical review of developments in the field from the early concepts of an endogenous opioid system to the current understanding of multiple receptor types and their interaction in regulating ingestive behavior. Opioids from all three opioid families may stimulate food intake, and some evidence exists that opioids may stimulate energy expenditure. Eating and drinking behavior is very complex and involves a number of components. Our understanding of the role of opioids in this process is shallow, and future research must be designed carefully to evaluate individual components of ingestive behavior.