Skipping a morning meal won’t ruin your day, research suggests. (Credit: Farknot Architect on Shutterstock)

‘The most important meal of the day’ may not be so important after all, at least for adults.

In A Nutshell

• A meta-analysis of over 3,400 people found virtually no cognitive difference between fasted and fed adults; the effect was just 0.02 standard units.
• Your brain switches from glucose to ketones after 12-16 hours without food, a natural adaptation that keeps mental performance stable during fasting.
• Fasting mainly hurt performance when people viewed food images; on neutral tasks, fasted people performed just as well or slightly better than fed participants.
• Children still benefit from breakfast, but for healthy adults, the science doesn’t support the “breakfast is essential for brain function” myth.

For decades we’ve heard the same advice. Breakfast is the most important meal of the day. Parents say it, doctors echo it, cereal companies print it on boxes. But science is catching up to that old belief, and the evidence tells a very different story.

A meta-analysis published in Psychological Bulletin looked at data from more than 3,400 people across 63 studies. The researchers wanted to know what really happens to your thinking when you skip a meal. The answer? Not much.

Across dozens of experiments testing memory, attention, and problem-solving, the average difference between people who had eaten and those who hadn’t was almost zero. Statistically speaking, fed participants performed just 0.02 standard units better — a gap so tiny it’s meaningless. In fact, the researchers’ model even suggested about a one-in-four chance that fasting groups performed a bit better, though the difference was so small it was likely random.

In other words, skipping breakfast won’t make you dumber.

Your Brain Runs on Two Fuels

Here’s the biology behind it. Most of the time your brain runs on glucose, the simple sugar your body gets from food. When you haven’t eaten for several hours, those sugar reserves start to dip. But instead of shutting down, your body flips a switch and begins using a backup fuel: ketones, made from stored fat.

Think of it like a hybrid car changing from gas to electric. The brain keeps running, just on a different source of energy.

This flexibility isn’t a modern trick; it’s ancient. Our ancestors often went long stretches between meals while hunting or gathering, and their brains had to stay sharp to survive. We’re built to think clearly whether we just ate or not.

Children benefit from nourishment in the AM more than adults. (Photo by Tima Miroshnichenko from Pexels)

What the Research Found

Researchers Christoph Bamberg and David Moreau pulled together decades of fasting studies. They compared how people performed after fasting anywhere from three hours to two weeks, with most fasts lasting about half a day.

When they ran the numbers, the pattern was remarkably consistent. Fasting for 8, 12, or even 16 hours didn’t affect memory, attention, or decision-making in any meaningful way. Short-term hunger just wasn’t enough to dull the mind.

There were a few small exceptions. Younger participants showed slightly more drop-off in performance than older ones. People tested late in the day did a little worse than those tested in the morning. And once fasting stretched beyond a full 24 hours, performance started to dip modestly. But most of us never fast that long in everyday life.

One quirky finding stood out: fasting only hurt performance when people were shown pictures of food. Looking at images of burgers and pizza while hungry made them slower and less focused. When the same people were given neutral memory or attention tests, they did just as well as those who had eaten.

So hunger mainly distracts you when you’re thinking about food, not when you’re doing normal mental tasks.

Kids Still Need Breakfast — Adults Don’t

Before parents start skipping grocery runs, one big caveat: these results apply to adults, not children. Kids’ brains are still developing and use a steadier stream of energy. Research shows that children, especially those with limited nutrition, learn and focus better after breakfast.

Adults, on the other hand, have fully developed brains that handle energy swings just fine. If you’re healthy, missing breakfast or eating later won’t drain your focus.

Feed the kids before school, but if you skip your morning toast on a busy day, don’t stress.

The Power of Expectation

One of the more fascinating parts of this research had nothing to do with food at all. People’s beliefs about fasting changed how they performed.

In one experiment, those who believed fasting would help them concentrate actually did better than those who feared it would make them sluggish. Everyone was equally hungry; the only difference was mindset.

So maybe the “breakfast myth” isn’t just cultural, it’s psychological. If you expect to feel foggy when you skip breakfast, you probably will.

What It Means for Intermittent Fasting

Intermittent fasting — skipping meals on purpose — has become hugely popular. Critics worry that going without food for long stretches might cloud your thinking at work or school.

According to this review, that fear doesn’t hold up. Studies on people who fast regularly, like those following 16-hour daily fasts, found no sign of cognitive impairment. Some even showed slight improvements once people got used to the routine.

That said, the research mostly covers healthy adults in Western countries. We still need more studies on older adults, people with medical conditions, and long-term fasting. But for most healthy people, the takeaway is simple: fasting won’t make you foggy.

The Bigger Picture

The myth that skipping breakfast hurts your brain has been around for more than a century. But when you look at the data, it just doesn’t hold up. Human brains evolved to stay alert whether we’ve eaten recently or not. The same adaptation that helped our ancestors stay sharp while hungry still works perfectly today.

So if you rush out the door without breakfast, or get caught in a long meeting before lunch, don’t feel guilty. Your brain isn’t falling apart, it’s just switching fuels.

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Disclaimer: This article is for general informational purposes and is not a substitute for medical advice. People with health conditions or special dietary needs should talk with a qualified healthcare provider before changing eating habits.

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Paper Summary

Methodology

The researchers conducted a systematic review and meta-analysis, searching multiple scientific databases for studies published from 1923 to February 2025. They included only studies that compared cognitive performance between fasted and satiated healthy adults using standardized psychological tasks. They analyzed 222 effect sizes from 63 studies involving 3,484 total participants. The median fasting duration was 12 hours, though studies ranged from three hours to 14 days. The researchers used Bayesian hierarchical models to account for differences between studies and to calculate the overall effect of fasting on cognitive performance.

Results

The analysis found no meaningful difference in cognitive performance between fasted and satiated participants (g = 0.02, with a 95% credible interval from -0.05 to 0.10). Longer fasting durations showed modest decreases in performance, with each additional hour of fasting associated with a 0.01 decrease in standard units. Younger participants showed larger performance decrements when fasted compared to older adults. Testing later in the day produced worse performance in fasted individuals. Tasks using food-related images showed impairment in fasted people, while neutral tasks showed no difference or slight improvements. Across different cognitive domains (attention, memory, executive function), no domain showed consistently larger effects than others.

Limitations

Most studies involved healthy young to middle-aged adults from Western countries, limiting generalizability to other populations. Many studies lacked precise reporting of fasting durations, blood glucose measurements, and testing times. Only four studies examined repeated intermittent fasting protocols, making it difficult to assess adaptation effects. The analysis excluded religious fasting practices like Ramadan due to confounding factors like water restriction. Individual differences in response to fasting were not captured in the group-level analyses. Some included studies had moderate to high risk of bias in their methodology.

Funding and Disclosures

The research was supported by the Royal Society of New Zealand Marsden Fund (Grant UOA193) and a University of Auckland Early Career Research Excellence Award to David Moreau. The authors declared no conflicts of interest.

Publication Details

Bamberg, C., & Moreau, D. (2025). Acute effects of fasting on cognitive performance: A systematic review and meta-analysis. Psychological Bulletin. Advance online publication. doi:10.1037/bul0000492

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