Why do we get hangry?

Posted by Susan Lubejko on November 5, 2020 in Behavioral Neuroscience, Emotions, Mood, Neuroscience | Leave a comment

I’ll admit it – I get very hangry. “Hangry” (a colloquial combo of “hunger” and “angry”) describes the grumpiness and irritability I experience when I’ve gone a bit too long between meals. Hunger itself is an important physiological feeling that signals when our body is low on energy that needs to be replenished by eating. Hunger can commonly manifest in other symptoms, such as headache or lightheadedness. But have you ever wondered how hunger can have such a profound effect on your mood and emotions?

Hunger, the body, and the brain

    The sensation of hunger is thought to be signaled by your digestive tract to your brain in two ways. First, blood glucose-sensitive cells in the body detect a decrease in blood sugar and send a signal to the brain that you need to eat. Older laboratory studies in which subjects received injections of insulin, which causes a sudden decrease in blood glucose, indicate that a drop in blood sugar results in bodily reactions such as increased salivation, sweating, tremors, and adrenaline levels in the blood [1,2]. This is important as these responses are all associated with activating the sympathetic nervous system. The sympathetic nervous system is a division of the autonomic nervous system, which regulates our unconscious bodily functions. The sympathetic nervous system is most well known for regulating our “fight or flight” behaviors. Its activation causes the release of the chemicals adrenaline and cortisol, which are well known for their roles in our “stress response.” So it isn’t too much of a stretch to see how hunger can lead to disgruntled behavior.

    The second major signal of hunger is the release of the chemical ghrelin from cells in the stomach. Ghrelin signals through both the blood and the large abdominal vagus nerve to important brain areas to induce eating. Ghrelin appears to be involved in a ton of different digestive and metabolic system functions, including the blood glucose control mentioned above. It can also cause the release of our stress-related hormone cortisol [3], further illustrating how hunger may lead to anxious behavior. 

Hunger and your behavior

    While we know that hunger leads to changes in the body that could be related to a stressful physiological response, hunger has also been shown to lead to impulsive and aggressive behavior. In rodents in the laboratory, an infusion of ghrelin directly into the brain to imitate hunger signals led rats to perform poorly and impulsively on decision-making tasks [4]. In humans in the laboratory setting, hunger correlated with subjects acting impulsively during a gambling task and exhibiting financially risky behavior, which switched to becoming risk-averse after a meal. This result is interestingly similar to the behavior of animals in the wild in which hungry animals become less choosy about their meals [5]. 

In one study, observation of married couples using blood sugar levels in the evening as a proxy for not having eaten found that partners with low blood sugar had more aggressive impulses, which was measured by how many pins they chose to stick into a voodoo doll of their spouse each evening (yikes!). They also showed more signs of aggression in a task in which they chose the intensity and duration of a noise blasted through headphones into their spouse’s ears. Participants with lower blood sugar were more likely to increase the intensity and duration of the sound (double yikes!) [6]. 

What are the conditions that produce hangriness?

    In general, hungriness (usually as measured by low blood sugar) has been associated with impaired cognitive function and adverse effects on emotions [7]. However, most people that have experienced hangriness would not report that they feel hangry every single time that they feel hungry. So, what are the precise conditions that take a feeling that compels you to eat and transforms it into hunger-induced rage?

    In 2019, researchers at the University of North Carolina at Chapel Hill set out to answer this question [8]. The researchers showed study participants a series of pictures. The first image was designed to invoke positive, negative, or neutral feelings. The second image was a completely neutral image of a Chinese character, which had no meaning to this group of participants, and the subjects were asked to rate the pleasantness or unpleasantness of the character. The researchers found that hungry subjects only rated the character as unpleasant when they were already primed with a negative image first (e.g. an image of an attacking wolf). 

In another study, the same researchers asked hungry university students to participate in a writing task in which they either wrote a story about a picture of a face expressing some emotion or about something emotionally neutral. Next, the subjects participated in a visual task. The catch is, this task was designed such that the computer they were using froze and crashed right before the end of the task. A research technician then approached the subject in an aggressive manner, demanding to know what the subject did to interfere with the task. Finally, the subjects self-reported their emotional state. The researchers found that hungry students reported hangriness and hateful feelings toward the research technician only, surprisingly, if they weren’t already primed to consider their emotions by the writing task (aka the students that were instructed to write about something emotionally neutral). 

    So, taken together, what does this mean? The presentation of hangriness is extremely dependent on context. It appears as though hangriness only manifests from hungriness when you are primed with an already negative emotional context (think: being hungry at home is very different from being hungry while stuck in a traffic jam). Also, interestingly, hangriness won’t manifest if you are already thinking about emotional state. It is thought that just having a readily accessible concept of emotions makes emotions more easy to regulate, thereby reducing the risk of becoming irrationally hangry. Perhaps the next time you feel yourself getting hangry, taking a moment to acknowledge the negative emotions will buy you enough time to grab a snack.

Can you combat your hanger?

    As is the case with a lot of human behaviors, hanger appears to encompass components of biological bodily functions, as well as intricate psychological perceptions of the situations in which it manifests. Our understanding of these components may provide us with keys to combating hanger’s negative effects, such as taking the opportunity to assess our internal thoughts and external environment. As a hanger sufferer, I can say that this is way easier said than done in the moment, but look forward to trying some of these techniques in the name of science. But I’ll keep a snack in my purse, just to be safe. 

References

1. Heller SR, MacDonald IA, Herbert M, Tattersall RB (1987) Influence of sympathetic nervous system on hypoglycaemic warning symptoms. The Lancet, 2:359-363
2. Corrall RJM, Frier BM, Davidson NMcD, Hopkins WM, French EB (1983) Cholinergic manifestations of the acute autonomic reaction to hypoglycaemia in man. Clinical Science, 64:49-53
3. Abdalla MMI (2015) Ghrelin – physiological functions and regulation. European Endocrinology, 11(2):90-95
4. Anderberg RH, Hansson C, Fenander M, Richard JE, Dickson SL, Nissbrandt H, Bergquist F, Skibicka KP (2016) The stomach-derived hormone ghrelin increases impulsive behavior. Neuropsychopharmacology, 41:1199-1209
5. Symmonds M, Emmanuel JJ, Drew ME, Batterham RL, Dolan RJ (2010) Metabolic state alters economic decision making under risk in humans. PLoS ONE, 5(6):e11090
6. Bushman BJ, DeWall CN, Pond RS, Hanus MD (2014) Low glucose relates to greater aggression in married couples. Proceedings of the National Academy of Sciences, 111(17):6254-6257
7. Taylor LA, Rachman SJ (1988) The effects of blood sugar level changes on cognitive function, affective state, and somatic symptoms. Journal of Behavioral Medicine, 11(3):279-291
8. MacCormack JK, Lindquist KA (2019) Feeling hangry? When hunger is conceptualized as emotion. Emotion, 19(2):301-319