Binge-eaters' behavior is triggered by the trifecta of deprivation, stress, and tempting foods that act on the brain in a way that is similar to heroin and other opiods:
From the rats' responses to these drugs, Boggiano and her colleagues inferred how stress and dieting change the brain's opioid control of eating. The binge eating occurred after rats experienced both foot shock (stress) and cyclic caloric restriction (dieting). Either caloric restriction or stress alone were not enough to produce changes in food intake, but stressed and underfed rats ate twice the normal amount of Oreo® cookies, which rats find rewarding. In other words, animals subjected to both stressors became binge eaters, confirming how strongly these outside factors interact to change eating behavior.
The findings also implicated opioids in the neurochemistry of binge eating. The highly rewarding butorphanol enhanced the binge eating; the reward-blocker naloxone suppressed how much the stress/deprived rats ate, to the level of the control rats. The authors say this pattern of findings in rats who were sated at the time of testing strengthens the evidence that reward, more than metabolic need, drives binge eating. Boggiano and her colleagues speculate that sensitized opioid-receptor signaling may be necessary to initiate binge eating. In the rats, stress and reduced calories seemed to sensitize those receptors to the presence of highly palatable food, in this case cookies. This, they write, "may underlie the common clinical observation that just a bite of highly palatable (often forbidden) food triggers binges and makes it difficult to abstain from binge eating…"
"Highly palatable food can mimic opioid drugs by releasing opioids or activating sensitized receptors, so imagine so imagine what it can do in a human with a history of dieting. If only rat chow is available, even rats with a history of dieting when stressed rats don't binge — but when they get a little bite of cookie first, they do." As a result, she says when treating bulimics and binge eaters, it may not be a good idea to introduce palatable (junk) food too early in therapy.
