"Does 'Being Hungry Makes You Unable to Think' a Myth?—A Large-Scale Study Reveals the Unexpected Relationship Between Fasting and the Brain"

"You Can't Think Clearly Without Breakfast"

This is a phrase many people have likely heard at least once since childhood. Before school tests, important work meetings, or long drives, it's natural to think that hunger reduces concentration, dulls judgment, and increases mistakes. In fact, the term "hangry," a combination of "hungry" and "angry," is widely used to describe irritability caused by hunger.

However, a large-scale review study examining the relationship between fasting and cognitive function is prompting a rather calm revision of this common belief.

In conclusion, short-term fasting in healthy adults does not necessarily significantly worsen performance on general cognitive tests. In fact, on average, no meaningful difference in cognitive performance was observed between those who were eating and those who were fasting.

Of course, this is not to say that "fasting is safe for everyone and the longer, the better." The study specifically addresses short-term fasting in healthy adults. Different considerations are needed for prolonged fasting, children and young people in growth phases, individuals with chronic illnesses, or those at risk of eating disorders.

Nonetheless, what makes this study intriguing is that it challenges the simple equation of "hunger = brain fuel depletion = decreased thinking ability."

What the Data from 3,484 People Showed

The study in focus is a systematic review and meta-analysis by Christoph Bamberg and David Moreau on the "Acute Effects of Fasting on Cognitive Performance." It analyzed 71 independent studies from 63 scientific papers, involving a total of 3,484 participants.

The studies analyzed compared the cognitive functions of people in a fasting state with those who ate normally. The evaluations included various abilities related to daily life, work, and learning, such as memory, attention, reaction speed, accuracy, decision-making, and inhibitory control.

The results showed that with short-term fasting of about 12 hours on average, there was no significant difference in cognitive performance between those fasting and those who ate. Statistically, there wasn't enough difference to definitively say "fasting dulls the mind."

This is a rather important insight considering modern eating habits.

For example, if you eat dinner at 8 PM and skip breakfast the next morning, eating lunch instead, the fasting time is about 16 hours. Many people try the so-called 16-hour fast or time-restricted eating. Or, some might miss breakfast due to a busy schedule and carry on with their morning work. The major takeaway from this study is that it's not necessary to assume "not eating means the brain won't work."

Where Did "You Can't Think Clearly Without Breakfast" Come From?

The debate over the importance of breakfast has a long history. Particularly for children, research and educational experiences have repeatedly suggested that eating breakfast is related to learning, attention, and school performance.

However, several factors are intertwined here.

Children who eat breakfast might also benefit from other factors such as family environment, sleep, lifestyle rhythm, and nutritional status. Additionally, the energy demands and brain development stages differ between growing children and adults. Therefore, the notion that "breakfast is important for children" should not be directly extended to "all healthy adults will experience decreased cognitive abilities if they skip breakfast."

The review also suggests that cognitive performance decline during fasting might be more noticeable in children and young people. This means the study does not entirely dismiss the value of breakfast. Rather, it indicates the need to consider who might be affected by fasting, to what extent, and under what conditions.

The question "Is breakfast important?" cannot be answered with a simple yes or no. Breakfast for children, breakfast for manual laborers, meals for people with chronic illnesses like diabetes, and breakfast for healthy adults with desk jobs each have different meanings.

Does the Brain Really "Stop Without Food"?

The anxiety surrounding fasting is often based on the well-known fact that "the brain uses a lot of glucose." Indeed, the brain is a major energy-consuming organ, and extreme drops in blood sugar levels are dangerous.

However, the human body is not so fragile that it stops functioning immediately after a few hours without food. There is energy stored as glycogen in the body, and as fasting time extends, the body starts using fat and ketone bodies as energy sources.

Of course, this metabolic switch varies from person to person. It is influenced by regular diet, sleep, exercise habits, body composition, health status, and familiarity with fasting. But at least for healthy adults, it's hard to say that memory and judgment visibly deteriorate just because they haven't eaten for a short period.

This might be surprising to those who view fasting as a dangerous act of willpower. On the other hand, for those who incorporate fasting or time-restricted eating into their daily lives, it might be a confirmation of what they suspected.

However, There Are Cautions for "Fasting Beyond 12 Hours"

An important aspect of this study is that while no major adverse effects were observed on average, cognitive performance decline was suggested under certain conditions.

One such condition is when fasting time extends. According to an article in ScienceAlert, fasting beyond 12 hours showed modest cognitive performance decline.

Another condition involves young participants, such as children and teenagers. The developing brain has different energy demands and physiological characteristics compared to adults. Although the data on young people in the overall study is limited, they might be more susceptible to the effects of fasting.

Differences also emerged depending on the content of the cognitive tests. Tasks using food-related stimuli were particularly susceptible to the effects of fasting. This is intuitively understandable; when hungry, seeing pictures or words related to food can divert attention. This suggests that rather than the entire brain dulling, there might be a tendency to be more easily distracted by food-related information.

This can also happen in everyday life. For instance, seeing restaurant ads while hungry or discussing food before lunch can disrupt concentration. However, this might be more about attention resources being diverted to appetite rather than a decline in mathematical calculation or reading comprehension skills.

On Social Media, Reactions to "Misleading Headlines"

 

The ScienceAlert article also garnered reactions on social media platforms like Reddit. Notably, there were reactions to the headline.

The headline "We Were Wrong About Fasting" is strong in attracting readers' interest. However, on social media, there were comments suggesting that it should clearly state what was wrong and that it seemed clickbait-like.

In reality, the article's content is not a simple narrative of "fasting was not dangerous" or "fasting was a panacea." More accurately, it presents a rather limited conclusion that "short-term fasting in healthy adults does not necessarily significantly impair general cognitive function."

Skipping over these limited conditions can lead to misunderstandings.

On social media, there were also cautious comments like "the lack of impact might mainly pertain to fasting up to about 12 hours" and "the point that there is a decline in children and teenagers should be emphasized." Such reactions demonstrate an important attitude when reading scientific articles: not judging by the title alone but confirming the subjects, conditions, research methods, and exceptions.

Meanwhile, some shared personal experiences like "I can concentrate even while fasting" or "I feel more mentally clear." Among those who have experienced long-term fasting, some feel mentally clear when entering ketosis. However, this is merely personal experience and should be considered separately from universally applicable scientific conclusions.

"Cognitive Function" and "Mood" Are Not the Same

An interesting point raised on social media was the suggestion that "even if cognitive function doesn't decline, emotions might be a different matter."

Indeed, even if memory or reaction speed on tests doesn't decline, some people become irritable when hungry. They might become grumpy at work, make hasty judgments, have prickly conversations, or feel bad even if they can concentrate before lunch. Many people have these experiences.

What's important here is that "cognitive performance" and "subjective mood" are different things.

Even if cognitive tests show no issues, the person might feel strongly hungry. While concentration scores might not change, stress, fatigue, drowsiness, and irritability might increase. Conversely, even if someone feels "not mentally sharp today," objective tests might not show a decline in performance.

If incorporating fasting into your life, it's important to understand this difference. The result "tests are fine" does not mean "the person can spend the day comfortably." It's necessary to consider not only work or study performance but also mood, relationships, sleep, meal quality, and exercise impacts.

Fasting Is Not a "Universal Health Method" but a "Tool with Significant Individual Differences"

In recent years, fasting and time-restricted eating have gained attention in contexts such as dieting, blood sugar control, inflammation, cardiovascular risk, and longevity. The idea that "when you eat" affects health, not just "how much you eat," has attracted many researchers and practitioners.

However, there is also a lot of extreme information about fasting.

"Just skipping breakfast will make you lose weight"
"Fasting awakens the brain"
"The longer you extend the time without eating, the healthier you become"
"Modern people eat too much, so everyone should fast"

Such assertions are risky. Some people are suited for fasting, while others are not. Skipping meals can disrupt eating rhythms, lead to rebound overeating, or worsen sleep for some individuals. People undergoing diabetes treatment, pregnant or breastfeeding women, growing children, those with a history of eating disorders, and the elderly may need to consult specialists.

This study does not recommend fasting for everyone. Rather, it alleviates the anxiety that "short-term fasting will always make you less intelligent" while indicating that caution is needed for long-term fasting and young people.

In other words, fasting is neither something to believe in like a religion nor something to uniformly dismiss as a dangerous trend. It is reasonable to view it as a "tool" to be used cautiously according to one's constitution and goals.

A Practical Interpretation for Working Adults

So, how can this study be applied to daily life?

First, if you are a healthy adult, skipping breakfast does not necessarily mean your thinking ability will collapse in the morning. Some people might feel better and concentrate better in the morning without breakfast. In such cases, there might be no need to worry excessively that "not eating breakfast makes me unhealthy."

On the other hand, some people clearly feel more stable and find it easier to get into work or study after eating breakfast. For them, breakfast may be an important habit.

The key is that "there is no average difference in studies" is not the same as "there is no difference for me." Studies show group trends but do not directly teach individual optimal solutions.

If you want to practice this, observe your condition. Compare concentration, mood, hunger, lunch amount, drowsiness, ease of exercise, and evening appetite on days you eat breakfast and days you don't. Ideally, observe over weeks rather than just a few days. It's important to look at the overall quality of life, not just changes in weight.

The "Limited Conditions" Needed When Reading Scientific Articles

This topic serves as a good example of how to read scientific news.

"Fasting Doesn't Dull the Mind"
"The Breakfast Myth Has Collapsed"
"The Brain Is Fine Even When Hungry"

These expressions are catchy but come with many conditions.

The subjects are mainly healthy adults. The median fasting time is 12 hours. Different trends exist for long-term fasting. Caution is needed for children and young people. Among cognitive functions, tasks related to food are more susceptible to impact. It does not completely deny mood or irritability.

Reading these limited conditions carefully enhances the value of the research. Science does not provide "answers that explain everything at once" but is an endeavor to approach reality by distinguishing conditions.

It's understandable that reactions like "scientists say different things every year" appear on social media. In nutrition and health information, past common knowledge is often revised later. However, this does not necessarily mean science is unreliable. It also means that with more data, better analysis methods, and more precise condition settings, we can gain a higher-resolution view than before.

Conclusion: Being Hungry Doesn't "Always" Dull the Mind

The large-scale review presented a simple yet important point.

In healthy adults, short-term fasting does not necessarily significantly impair general cognitive function. At least, the image that memory and judgment will always decline just by skipping one meal might need reconsideration.

However, this does not unconditionally recommend fasting. Caution is needed for long-term fasting, young people, people with chronic illnesses, and those who experience negative impacts on mood or health. While test scores might not drop when hungry, irritability, discomfort, and impacts on relationships do not disappear.

Fasting is neither magic nor an enemy.

Those who feel balanced by eating breakfast should eat it. Those who concentrate better without eating, as long as there are no health issues, can choose that rhythm. The important thing is to move away from the belief that "breakfast is absolute" or "fasting is absolute" and think flexibly according to your body and goals.

The phrase "you can't think clearly when you're hungry" is not entirely wrong. However, at least for short-term fasting in healthy adults, it doesn't seem to be that simple.

Our brains might be slightly more resilient to hunger than we think.

Source URL

ScienceAlert: The article introducing the large-scale review on fasting and cognitive function that is the subject of this article
https://www.sciencealert.com/we-were-wrong-about-fasting-massive-study-finds

Overview of the study published in Psychological Bulletin: Research information, number of subjects, effect size, and conclusions of "Acute Effects of Fasting on Cognitive Performance: A Systematic Review and Meta-Analysis" by Christoph Bamberg and David Moreau
https://uni-salzburg.elsevierpure.com/en/publications/acute-effects-of-fasting-on-cognitive-performance