Aug 23 (BBC) – Diets are widely celebrated as the noble, often celebrity-endorsed, route towards improved health and wellness – and form the basis of a booming $250bn (£203bn) industry.
But let’s face it: dieting can also be miserable.
One study of almost 2,000 overweight and obese people who wanted to lose weight found that those who actually managed to do so were nearly 80% more likely to have symptoms of depression than those who didn’t.
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It’s hardly a compelling sales pitch for cutting calories, but being hungry can mess with our minds in manifold ways – not least by making us “hangry”, that familiar feeling of rage that erupts when it’s 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 we’ve outlined in our recent book about the internal and external factors that influence and manipulate the way we think, all these things ultimately affect how well we reflect and make decisions.
This is a problem that goes much deeper than dieting. In a world where many people struggle to feed themselves, it’s 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 don’t really understand or acknowledge them. That’s because it’s easier to regulate our emotions when we’re 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 you’re 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 you’re trying to sell a jacket online after watching a sad movie, you are likely to market it at a lower price.
But what’s this got to do with how recently we’ve eaten?
Well, hunger appears to be a reliable driver of negative emotions and low mood. In one 2022 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 weren’t small effects,” says Jonker. In fact, the hungry women reported, on average, feeling more than twice as angry as those who weren’t 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 people’s 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 they’d 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 doesn’t just make us feel negative and low, however. It can also make us both impulsive – something to be aware of if you’re 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.
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 haven’t eaten.
According to Lindquist, it’s 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 weren’t 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 Lindquist’s finding that hungry people who don’t 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 wouldn’t be irritated at all by a slight from your co-worker, but when you’re 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.
Jonker’s 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.
Jonker’s 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 you’re 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 we’re 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 weren’t 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 we’re 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 we’re 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 isn’t 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 doesn’t affect the task performance because the task is simple enough.”
Researchers discovered that the more people’s minds were wandering, the worst they performed on the task
He set out to test the extent to which famished people are affected by mind wandering in a complex task – reading 27 pages of the epic novel War and Peace followed by a reading comprehension test. They were also asked whether their minds were wandering and, if so, what they were thinking about. In the test, 39 people were asked to show up to the laboratory without eating for five hours, while 91 were told to arrive satiated. Among the latter group, 46 people got to listen to a recording of an erotic story to see if that increased mind wandering.
The researchers discovered that the more people’s minds were wandering, the worst they performed on the task. And the hungry group was the most prone to mind wandering – those individuals did it 10% more than the two other groups, and were mainly thinking about food. Being hungry, this seems to imply, is potentially even more distracting than sex.
But this may not just be down to poor attention. Hunger also appears to reduce cognitive flexibility, which is hugely important during any kind of cognitive task, including reading comprehension. This executive function, which helps with complex thinking but is distinct from IQ, enables us to switch perspective easily and abandon strategies that are no longer working in favour of better ones.
John Parkinson, a psychologist at Bangor University in the UK, has shown that hungry people who are distracted by thinking about food are more likely to make errors on a task measuring cognitive flexibility.
“The parallel here is with the fear and anxiety literature,” explains Parkinson. “If I put you into an anxious state by showing you a picture of snakes or whatever, you actually narrow your cognitive focus. So, you’ll reduce your cognitive flexibility and you’ll really focus on how to get rid of the snake.”
Similarly, our thinking can become significantly impaired when we’re starved and trying to get rid of the sensation. If you are trying to solve problems at such times, you “may choose simpler, immediate solutions rather than long-term, complex solutions”, says Parkinson.
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 we’re 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 we’re 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 we’re 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 don’t 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 you’re really just hungry.
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