Its hardly a compelling sales pitch for cutting calories, but being hungry can mess with our minds in manifold ways not least by making us hungry, that familiar feeling of rage that erupts when its been too long between meals.
In fact, research is starting to reveal that fasting can negatively affect everything from our emotions to our cognition and judgement, at least in the short term. And, as weve outlined in our recent book about the internal and external factors that influence and control the way we think, all these things affect how well we reflect and make decisions.
This is a problem that goes much deeper than dieting. In a world where many people strive to feed themselves, its worth remembering that hunger can boost inequality. One study found that the provision of school meals in Indian schools improved the cognitive performance of students by 13% to 16%.
Without sufficient nutrients and calories, it is hardly surprising our brains might struggle to develop and function properly. But how can everyday hunger also affect how we think?
Emotions have a profound influence on how we think particularly when we dont really understand or acknowledge them. Thats because its easier to regulate our emotions when were aware of where they come from and how they influence our thinking and decision making.
Low mood often makes us more pessimistic, for example, which biases our thinking to be more negative. And if youre not fully aware how worried you are about an upcoming medical test, research shows you will be more risk-averse when taking an unrelated financial decision. Similarly, if youre trying to sell a jacket online after watching a sad movie, you are likely to market it at a lower price.
But whats this got to do with how recently weve eaten?
Well, hunger appears to be a reliable driver of negative emotions and low mood. In one 2023 study, psychologist Nienke Jonker and colleagues from the University of Groningen in the Netherlands asked 129 women around half of whom had been asked to fast for 14 hours questions about their hunger level, eating habits and mood. And they found that the hungry women reported more negative emotions, including higher tension, anger, depression, fatigue and confusion. They also reported lower positive emotions, such as vigour.
They werent small effects, says Jonker. In fact, the hungry women reported, on average, feeling more than twice as angry as those who werent famished. They were, quite literally, hangry.
Low mood can radically change how we interpret the world. If you are in a negative mood, then you remember negative things better which may put you in an even worse mood.
This negative framing can lead to errors in interpreting our surroundings causing us to see the world in simplistic black-and-white terms and miss the all-important nuance. When we feel down, we also pay more attention to negative details than positive ones, which may make us feel bad about ourselves and wary of others.
In another series of experiments, Kristen Lindquist, a psychologist and neuroscientist at the University of North Carolina, Chapel Hill, in the US, and colleagues found that hunger increases peoples tendency to be manipulated by negative emotions. They showed 218 workers (some of whom were hungry) neutral, positive and negative images (such as an angry dog), and then asked them to use their gut feeling to determine whether a more ambiguous image (a Chinese pictograph) was positive or negative.
Those who had been shown a negative image first were more likely to rate the pictograph as negative, even though theyd been instructed not to be influenced by the previous pictures. And yes, the participants who had described themselves as hungry before taking the test were more likely to be manipulated in this way.
Hunger doesnt just make us feel negative and low, however. It can also make us both impulsive something to be aware of if youre penning your resignation letter before lunch and punitive. A famous 2011 study of Israeli parole judges appears to show just how much the latter might influence our decision-making. Hunger is a powerful signal because it ultimately helps us to survive
Cognitive flexibility is also needed for simple decisions such as what to eat. If were on a diet, for example, we need to be flexible to fight the intense urge to eat fatty, carbohydrate-laden foods. But if we go shopping when were hungry and mentally rigid in this way, adds Parkinson, we just buy a whole lot of crap.
Hunger is a powerful signal because it ultimately helps us to survive. But, as a result, it can deeply interfere with our thinking. When were hungry, we will likely struggle with complex cognitive tasks, nuance and concentration and opt for simpler thinking approaches often driven by bias and prejudice. Being irritable, impulsive, punitive and stuck in the present particularly when we dont realise that these feelings are simply down to hunger will further muddle our minds.
But being aware of this can be hugely useful. The next time you are angry or low, for example, it may help to ask yourself whether youre really just hungry.
We are all prone to negative thoughts about the world, but that we can regulate them until hunger breaks down our ability to do so
It discovered that the judges were more lenient at the start of the day and just after lunch, when they were full, than just before lunch or at the end of the day. While this study has been criticised the effect could have resulted from other factors, such as how the cases were scheduled, rather than the judges hunger levels science does support the notion that we become more punitive when we havent eaten.
According to Lindquist, its hard to determine the cause of effects found in studies conducted in real world situations, such as during parole board hearings there are always alternative, possible explanations. But you can often control for these under laboratory conditions.
To test whether people really were harsher towards others when hungry, then, Lindquist invited 236 people into her lab. About half had fasted for at least five hours while the other half had eaten beforehand. They were then asked to perform a tedious task rotating geometric shapes on a computer before it suddenly crashed (or so they thought) forcing them to start over and do it all again.
At the end of this frustrating exercise, the participants were given the opportunity to review the researcher and potentially deliver a little passive aggressive retribution.
People who were hungry, especially those who werent paying attention to their emotions or focused on their internal state, were more likely to rate the researcher as judgmental [a negative verdict the researchers took to be punitive] on a little rating sheet we provided, says Lindquist.
The exact reasons why hunger makes us feel and behave in this way are complex. It could be down to an impairment in self-control that arises when blood glucose levels are depleted by fasting. This theory seems to suggest that we are all prone to negative thoughts about the world, but that we can regulate them until hunger breaks down our ability to do so.
The feelings that are generated in your body when hungry turn up the dial on what you are experiencing Kristen Lindquist
The view has been criticised, however, and other theories are becoming increasingly popular. Lindquist, for example, believes that feelings such as hanger are really just a misinterpretation of a physiological state as an emotional one. This is supported by Lindquists finding that hungry people who dont reflect on their emotions are more likely to misinterpret them and end up more angry and punitive as a result.
The feelings that are generated in your body when hungry turn up the dial on what you are experiencing in that context, explains Lindquist. So maybe you normally wouldnt be irritated at all by a slight from your co-worker, but when youre hungry you think it was a horrible thing to say.
This idea might be a game changer for people on diets. If the negative mental aspects of feeling hungry are caused by us misinterpreting a physical sensation, we could perhaps learn to reinterpret that physical sensation in a better way. This could work in a similar way to cognitive behavioural therapy (CBT), helping us to reframe our thoughts and feelings.
Jonkers study on the emotions of hungry women appears to back this up she found that women with symptoms of eating disorders experienced more positive feelings when hungry than women without such symptoms. Although eating disorders are complex mental health conditions, the findings suggest these women had relearned the normal association of hunger as a negative experience.
Jonkers study on the emotions of hungry women appears to back this up she found that women displaying some of the symptoms of eating disorders experienced more positive feelings when hungry than other women. Although eating disorders are complex mental health conditions, the findings suggest these women had relearned the normal association of hunger as a negative experience. While such mental reframing is highly counterproductive and dangerous when youre battling an eating disorder, Jonker is looking at ways it can be used in more positive ways.
There are evolutionary reasons why we might misinterpret hunger as something deeply unpleasant. After all, when were running low on nutrients, our brains need us to act rather than sit around contentedly with our feet up.
From an evolutionary standpoint, it makes sense that hunger would be accompanied by the impulse to go out and forage for things to maybe prioritise immediate gains as opposed to long-term gains, adds Lindquist.
Food restriction also affects cognition more directly
Indeed, a study from the University of Dundee in the UK showed that people do become increasingly biased towards the present when they are hungry and struggle to delay gratification.
The researchers offered study participants an immediate reward of either 20 cash or 20 song downloads or double that amount in the future. If the participants werent hungry, they were willing patiently to wait for 90 or 20 days, respectively, for the bigger reward. But among the hungry participants, these numbers shrank to 40 and 12 days, respectively. And that makes sense if the hunger signal is intended to spur us into action now, rather than plan for a more distant future.
Food restriction also affects cognition more directly. A 2021 review of the research investigating the effects of fasting on cognition found that attention and cognitive flexibility, the ability to switch between different tasks, are particularly affected.
Most of us will know what it feels like to have our attention hijacked by persistent thoughts of gooey chocolate cake, hot, crisp chips, or spicy noodles when were hungry. And research has shown this is very common hunger increases our attention to cues related to food. Again, this is also in keeping with the idea that the point of the physiological feeling of hunger is to make us go out and get food and that shifting our attention away from whatever else were doing is the first stage of this process.
In the modern world, and particularly in the West, it is rarely difficult to obtain food though. So being distracted by hunger isnt that useful anymore. It can create more disadvantages than advantages.
Jan Rummel, a cognitive psychologist at the University of Heidelberg in Germany and colleagues tested whether being hungry makes people more prone to intrusive mind-wandering, such as fantasising about food.
Usually, if you find people mind-wandering, the performance in a task they are doing goes down, he explains, adding that this effect only applies when the task is sufficiently complex, such as reading. If we are ironing or something, then I think we can have our minds wander and it doesnt affect the task performance because the task is simple enough.
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Its hardly a compelling sales pitch for cutting calories, but being hungry can mess with our minds in manifold ways not least by making us hungry, that familiar feeling of rage that erupts when its been too long between meals.
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