Endogenous opioids are released during stress and are known to be important for adaptive effects such as resistance to pain. They are also involved in motivational and reward processes in eating behavior, such as the stimulation of appetite by palatable foods. Perhaps the best evidence for opioid involvement in an interaction between stress and eating is the finding that, in animals and human infants, the ingestion of sweet and fatty foods, including milk, alleviates crying and other behavioral signs of stress. Recently, this effect was shown to depend on sweet taste rather than calories, as non-nutritive sweeteners also reduce crying. This stress-reducing effect can be blocked by opioid antagonists. The conclusion that adults select sweet fatty foods for opioid-mediated relief of stress is tempting, but remains speculative. Also, such behavior would need to be explained in the context of stress itself enhancing endogenous opioid release.
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