Feeling sated can become a cue to eat more

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When hunger pangs strike, we usually interpret them as a cue to reach for a snack; when we start to feel full, we take it as a sign that we should stop eating. However, new research shows that these associations can be learned the other way around, such that satiety becomes a cue to eat more, not less. The findings, published in Psychological Science, a journal of the Association for Psychological Science, suggest that internal, physical states themselves 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,” says psychological scientist Mark E. Bouton of the University of Vermont, one of the authors on the study. “If so, dieters might ‘relapse’ to eating, or perhaps overeating, when they feel full again.”

To test this hypothesis, Bouton and co-author Scott T. Schepers conducted a behavioral conditioning study using 32 female Wistar rats as their participants. Every day for 12 days, the rats, who were already satiated, participated in a 30-minute conditioning session. They were placed in a box that contained a lever and learned that they would receive tasty treats if they pressed that lever. Then, over the next 4 days, the rats were placed in the same box while they were hungry, and they discovered that lever presses no longer produced treats.

Through these two phases, the rats were conditioned to associate satiety with receiving tasty food and hunger with receiving no food. However, what would the rats do if they were placed in the box again? The results were clear: When the rats were tested again, they pressed the lever far more often if they were full than if they were hungry. In other words, they relapsed back to 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 explains.

This relapse pattern emerged even when food was removed from the cage before both the learning and unlearning sessions, indicating that the rats’ internal physical states, and not the presence or absence of food, cued their learned behavior. Findings from three different studies supported the researchers’ hypothesis that hunger and satiety could be learned as contextual cues in a classic ABA¹ (sated-hungry-sated) renewal design. However, the researchers found no evidence that an AB design², in which the rats learned and subsequently inhibited the lever-treat association in a hungry state and were tested in a sated state, had any effect on the rats’ lever pressing. Together, these results show that seeking food and not seeking food are behaviors that are specific to the context in which they are learned.

Although our body may drive food seeking behavior according to physiological needs, this research suggests that food-related behaviors can become associated with internal physical cues in ways that are divorced from our physiological needs. “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,” say Schepers and Bouton. “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.”

¹A-B-A design involves establishing a baseline condition (the “A” phase), introducing a treatment or intervention to effect some sort of change (the “B” phase), and then removing the treatment to see if it returns to the baseline (“A”).

²An AB design is a two part or phase design composed of a baseline (“A” phase) with no changes, and a treatment or intervention (“B”) phase.

Adapted from: Scott T. Schepers, Mark E. Bouton. Hunger as a Context: Food Seeking That Is Inhibited During Hunger Can Renew in the Context of Satiety. Psychological Science, 2017; 095679761771908 DOI: 10.1177/0956797617719084

Nutrtition Tip of the Day

Package your own healthy snacks! Put cut-up veggies and fruits in portion-sized containers for easy, healthy snacking on the go, without the added sugars and sodium.

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Brain cells that control appetite identified for first time

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Dieting could be revolutionized, thanks to the ground-breaking discovery by the University of Warwick on the key brain cells which control our appetite. Professor Nicholas Dale in the School of Life Sciences has identified for the first time that tanycytes, cells found in part of the brain that controls energy levels, detect nutrients in food and tell the brain directly about the food we have eaten. According to the new research, tanycytes in the brain respond to amino acids found in foods, via the same receptors that sense the flavor of amino acids (“umami” taste), which are found in the taste buds of the tongue. Two amino acids that react most with tanycytes, and therefore are likely to make you feel more full, are arginine and lysine.

These amino acids are found in high concentrations in foods such as pork shoulder, beef sirloin steak, chicken, mackerel, plums, apricots, avocadoes, lentils and almonds. Therefore, eating those foods will activate the tanycytes, based on the research, and make you feel less hungry more quickly. The researchers made their discovery by adding concentrated amounts of arginine and lysine into brain cells, which were made fluorescent so that any microscopic reactions would be visible. They observed that within thirty seconds, the tanycytes detected and responded to the amino acids, releasing information to the part of the brain that controls appetite and body weight. They found that signals from amino acids are directly detected by the umami taste receptors by removing or blocking these receptors and observing that the amino acids no longer reacted with tanycytes.

Nicholas Dale, who is Ted Pridgeon Professor of Neuroscience at the University of Warwick, commented: “Amino acid levels in blood and brain following a meal are a very important signal that imparts the sensation of feeling full. Finding that tanycytes, located at the centre of the brain region that controls body weight directly sensing amino acids, has very significant implications for coming up with new ways to help people control their body weight within healthy bounds.” This major discovery opens up new possibilities for creating more effective diets, and even future treatments to suppress one’s appetite by directly activating the brain’s tanycytes, bypassing food and the digestive system. Nearly two thirds of the UK population is overweight or obese and one third of the U.S. population is obese. This excess weight elevates the risk of premature death and a range of illnesses, such as cancer, diabetes, cardiovascular disease and stroke, which greatly reduce quality of life. A new understanding of how appetite functions could curb the growing obesity crisis.

The research, ‘Amino Acid Sensing in Hypothalamic Tanycytes via Umami Taste Receptors’, will be published in Molecular Metabolism and is funded by the Biotechnology and Biological Sciences Research Council.

Adapted from: University of Warwick. (2017, September 27). Brain cells that control appetite identified for first time: Dieting could be revolutionized, thanks to the groundbreaking discovery by the University of Warwick of the key brain cells which control our appetite. ScienceDaily. Retrieved December 21, 2017 from http://www.sciencedaily.com/releases/2017/09/170927093254.htm

Nutrition Tip of the Day

Make snacks count! Be sure your snack consists of protein, whole grains and healthy fat for the trifecta that will keep you feeling fuller longer.

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