The holiday season is upon us and with it the opportunities to enjoy festive treats. The proverbial saying that you eat with your eyes first seems especially relevant this time of year.
However, the science behind eating behavior reveals that the process of deciding what, when and how much to eat is much more complex than simply consuming calories when your body needs fuel. Hunger cues are only part of why people choose to eat. As a scientist interested in the psychology and biology that guides eating behavior, I am interested in how the brain’s experience with food shapes eating decisions.
So how do people decide when to eat?
Eat with your eyes
Visual cues related to food can shape the feeding behavior of both humans and animals. For example, wrapping food in McDonalds packaging is enough to improve the taste experiences of small children in many foods, from chicken nuggets to carrots. Visual food-related cues, such as the display of a light when food is delivered, can also promote overeating behavior in animals by bypassing energy needs.
In fact, a whole range of sensory stimuli, sounds, smells, and textures, can be associated with the pleasurable consequences of eating and influence decisions about food. This is why hearing a food brand’s catchy radio jingle, seeing a restaurant’s television ad, or walking past your favorite eatery can change your consumption decision and sometimes overdo it.
However, your ability to learn from food-related cues extends beyond stimuli from the outside world to include your body’s internal environment. In other words, you also tend to eat with your stomach in mind, and you do so using the same learning and brain mechanisms involved in processing food-related stimuli from the outside world. These internal signals, also called interoceptive cues, include feelings of hunger and satiety that come from your gastrointestinal tract.
It’s no surprise that signals from your gut help determine when to eat, but the role of these signals goes deeper than you might expect.
Trust your gut
Feelings of hunger or satiety serve as important interoceptive cues that affect food intake.
To study how interoceptive states shape eating behavior, researchers trained laboratory rats to associate feelings of hunger or satiety with whether or not they received food. They did this by giving the rats food only when they were hungry or full, so that the rats were forced to recognize internal cues to calculate whether food would be available or not. If a rat is trained to wait for food only when hungry, it will usually avoid the area where food is available when it feels full because it does not expect to receive food.
However, when the rats were injected with a hunger-triggering hormone called ghrelin, they approached the food delivery site more often. This suggests that the rats used this artificial hunger state as an interoceptive cue to predict food delivery and subsequently behaved as if they were expecting food.
Interoceptive states are sufficient to shape feeding behavior even without external sensory cues. One particularly striking example is mice that have been genetically modified to be unable to taste food, but still show preferences for certain foods based on caloric content alone. In other words, rodents can use internal cues to shape their food-related decision-making, including when and where to eat and what foods they prefer.
These findings also suggest that the sensation of hunger and the perception of nutrients are not limited to the stomach. They also contain brain areas important for regulation and homeostasis, such as the lateral hypothalamus, and brain centers involved in learning and memory, such as the hippocampus.
What happens in the vagus
The gut-brain axis, or the biochemical connection between the gut and the brain, shapes feeding behavior in many ways. One of them concerns the vagus nerve, a cranial nerve that helps, among other things, control the digestive tract.
The vagus nerve quickly transmits nutrient information to the brain. Activation of the vagus nerve can induce a pleasurable state in which mice voluntarily perform behaviors such as sticking their noses through an open gate to stimulate their vagus nerve. Importantly, the mice also learned to prefer foods and places where vagus nerve stimulation occurred.
The vagus nerve plays an essential role in not only transmitting digestive signals, but also a host of other interoceptive signals that can influence your emotions and behavior. In humans, vagus nerve stimulation can improve learning and memory and can be used to treat major depression.
The benefits of interoceptive awareness
Your body’s ability to use both external and internal cues to regulate how you learn and make decisions about food highlights the influential processes involved in regulating your energy needs.
Poor interoceptive awareness is associated with several poor feeding behaviors, such as eating disorders. For example, anorexia can be caused by a failure of interoceptive signals such as hunger to trigger the motivation to eat. Alternatively, the inability to use satiety to suppress the rewarding and pleasurable consequences of eating palatable food may lead to binge eating.
Your interoceptive signals play an important role in regulating your daily eating habits. Eating during the holidays comes with many stressors from the outside world, such as busy social calendars, pressure to conform, and feelings of guilt for overindulging. At this time, it is especially important to develop a strong connection with your interoceptive signals. This can help promote intuitive eating and a more holistic approach to your eating habits. Instead of fixating on external factors and setting conditions on your eating behavior, enjoy the moment, consciously enjoy each bite, and give your interoceptive signals time to play the role they were designed to play.
Your brain evolved to sense your current energy needs. By integrating these signals into your experience of your food environment, you can both optimize your energy needs and enjoy the season.
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Image Source : theconversation.com