“Come on, little fella – we should get going now.” But my son was not listening. The sand in the playground was just right, so he kept digging with his new toy excavator.
As I drifted back to my list of to-dos, however, the laughter was suddenly replaced by sobs. My son was not hurt, just very upset. When I looked at my phone, I saw it was well past his regular mealtime – and he was feeling very hungry.
However old we are, we all have a tendency to grow irritated if our body lacks enough fuel. But while humans have experienced this for as long as we have been on the planet, a specific word to describe the phenomenon only entered the Oxford English dictionary in 2018. “Hangry: to be bad-tempered or irritable as a result of hunger.”
Perhaps more surprising is the scarcity of research into how hunger affects people’s everyday moods. Most studies on food and mood have focused on patients with metabolic or eating disorders – perhaps because many psychologists have traditionally understood hunger to be such a basic physiological process.
So, with colleagues from the fields of psychology and mental health, I decided to investigate how different people respond to feeling hungry. We wanted to see if (and why) some people are better at reacting calmly when hunger strikes. Perhaps there would be some lessons for those of us with young children, too.
Surprising results
In the animal world, hunger is frequently studied for its role as a key motivator. Hungry rodents, for example, will vigorously press a lever or climb over large walls to get to food rewards. In the wild, hungry animals often roam further to explore their environment, seeming restless as they seek to overcome the threat of low or no energy.
To investigate the relationship between energy levels, hunger and mood in people, we equipped 90 healthy adults with a continuous glucose monitor for a month. Glucose is the primary source of energy for the body and brain, and these monitors – used in clinical practice to help patients with diabetes regulate their blood sugar levels – report values every few minutes. (Participants could actively check their glucose levels using the sensor app, and we could see when they accessed them.)
We also asked our participants to complete mood check-ins on their smartphones up to twice a day. These included questions about how hungry or sated they felt on a scale from 0 to 100, as well as a rating of their current mood.
The results surprised us. First, people were only in a worse mood when they acknowledged feeling hungry – not simply when they had lower blood sugar levels. And second, people who more accurately detected their energy levels in general were less prone to negative mood swings.
This suggests there is a key psychological middle step between a person’s energy and mood levels, which scientists call interoception.
In the brain, hunger is signalled by neurons in the hypothalamus that detect a prolonged energy deficit. Conscious feelings of hunger are then linked to the insula, a part of the cerebral cortex that is folded deep within the brain, and which also processes taste and plays a role in feeling emotions.
In our recent study, people with high interoceptive accuracy experienced fewer mood swings. This does not mean they never felt hungry – they just seemed better at keeping their mood levels stable.
This is important, because a sudden change in mood can have knock-on effects on relationships with family, friends and colleagues. It can lead to bad decision-making and more impulsive behaviour – including buying fast-energy food that can be less good for you.
More generally, paying close attention to our bodies’ needs helps keep our minds at ease too, avoiding unnecessary wear and tear on both. Deviating too much from the body’s ideal state can pose a long-term risk to our health – mental as well as physical.
Caught off-guard
Young children find it hard to interpret all the signals from their rapidly developing body. They are also easily distracted by what is happening around them, and often fail to attend to their hunger or thirst without prompting – leading to a sudden meltdown like my son had in the playground.
Likewise for many adults in today’s fast-paced world full of digital distractions, it can be easy to be caught off-guard by dipping energy levels. One simple life hack is to keep a regular meal schedule, because hunger often kicks in when we skip a meal.
Everyone’s energy levels ebb and flow, of course. But it is possible to improve your interoceptive accuracy by allowing your inner systems to pay closer attention to your energy levels. In addition, exercise and physical activity can sharpen your hunger sensing and improve energy metabolism.
Most of the time, of course, our moods are only modestly affected by hunger, among the many other factors that can come into play. But one of the lessons of my time at the playground has been to take care of my son’s food needs long before they become obvious. Perhaps we all need to be more aware of the risk of getting hangry.
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