Feeling full can cue desire to eat more, study suggests

The findings suggest that internal, physical states can serve as contexts that cue specific learned behaviors.
By Amy Wallace  |  Oct. 2, 2017 at 9:46 AM
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Oct. 2 (UPI) -- New research with rats shows the cues people get to eat when hungry or stop when full can be reversed with conditioning.

The study, published Friday in Psychological Science, found internal, physical states can serve as contexts that cue specific learned behaviors.

"We already know that extreme diets are susceptible to fail. One reason might be that the inhibition of eating learned while dieters are hungry doesn't transfer well to a non-hungry state," Mark Bouton, a psychological scientist at the University of Vermont, said in a press release. "If so, dieters might 'relapse' to eating, or perhaps overeating, when they feel full again."

Researchers tested their theory on 32 Wistar rats by placing rats in a box that contained a lever, training them to receive a treat if they pressed the lever every day for 12 days -- even though the rats were already satiated. Then, for four more days, the rats were placed in the same box when they were hungry, but pressing the lever no longer produced treats.

The rats were conditioned to associate satiety with receiving food and hunger with receiving no food. When the rats were tested again, researchers found they pressed the lever far more often if they were full than if they were hungry, relapsing into seeking treats.

"Rats that learned to respond for highly palatable foods while they were full and then inhibited their behavior while hungry, tended to relapse when they were full again," Bouton said.

The study showed the relapse pattern happened even when food was removed from the cage before both the learning and unlearning sessions, meaning that the rats' internal physical states and not the presence or absence of food was what cued the learned behavior.

The findings support the theory that hunger and satiety could be learned as contextual cues.

"A wide variety of stimuli can come to guide and promote specific behaviors through learning. For example, the sights, sounds, and the smell of your favorite restaurant might signal the availability of your favorite food, causing your mouth to water and ultimately guiding you to eat," Bouton said.

"Like sights, sounds, and smells, internal sensations can also come to guide behavior, usually in adaptive and useful ways: We learn to eat when we feel hunger, and learn to drink when we feel thirst. However, internal stimuli such as hunger or satiety may also promote behavior in ways that are not so adaptive."

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