The Truth About Fasting and Focus

Did your Granny used to tell you “Don’t skip breakfast, you’ll lose focus!”? Maybe those snack adverts warning that “you’re not you when you’re hungry” have lingered as genuine life advice over the years. Messages like these have quietly shaped the way we think about food and productivity: Eat regularly, stay sharp.

But as fasting has crept into mainstream Western-wellness, a question has lingered for me:

Is fasting healthy for both the mind AND the body, or does a lack of sustenance make our minds unravel?

After recently reading a major review exploring this, I was fascinated to discover that many of my long-held beliefs about fasting and mental clarity might not be quite right...

What the research says

A sweeping meta-analysis pulling together 71 studies over nearly seven decades found something surprising:

For healthy adults, fasting doesn’t significantly affect cognitive performance.

Participants performed just as well on tests of memory, attention, and problem-solving whether they’d recently eaten or not.

This means that those foggy morning meetings or “hangry” moments might not reflect a genuine drop in brain function after all, even if they feel that way. Our minds could simply be interpreting the body’s hunger cues as tiredness or stress, rather than an actual loss of cognitive ability. So it's more to do with how we emotionally associate with a feeling of hunger, which is something we have more power over than we might realise.

How fasting affects us

The body’s relationship with food is super smart. When we eat regularly, the brain runs mostly on glucose, stored as glycogen. But after roughly 12 hours without food, glycogen stores fade and the body switches to using ketones, which is a clean, fat-derived energy source that can sustain the brain just fine.

It’s a mechanism our ancestors depended on through centuries of feast and famine and it’s now being revisited for its potential benefits, from improved insulin sensitivity to the cellular spring clean known as autophagy, where old or damaged cells are recycled to keep us functioning at our best.

Nope, I didn't know that word either...

autophagy (noun)

biology

Consumption of the body’s own tissue as a metabolic process occurring in starvation and certain diseases:

"the process of starvation-induced autophagy was recently the focus of extensive research"

destruction of damaged or redundant cellular components occurring in vacuoles within the cell.

So why do some people still feel foggy when fasting?

The review found a few key exceptions that make sense once you think about them:

Children and teens – Their developing brains do seem to struggle without breakfast. It’s one reason the “breakfast before school” advice still stands strong.
Timing – Later in the day, fasting might amplify natural dips in alertness. So if your work relies on sharp focus in the afternoon, fasting windows may need some tweaking.
Food cues – When participants were shown images of food, fasted individuals got distracted more easily. (Who hasn’t been caught daydreaming about lunch mid-meeting?)

So, rather than fasting creating “brain fog”, it seems hunger simply draws our attention to… well, food.

What this means in real life

For most healthy adults, these findings are reassuring. You can explore intermittent fasting for metabolic health, weight balance, or simply to tune into your body’s natural rhythms, without fear that your brain will shut down.

But as always, context is key.

Fasting can feel empowering for some and depleting for others. If you’re managing long, complex days, emotionally demanding work, or fluctuating energy, it may be worth experimenting gently rather than straight in at a 16:8 fasting schedule.

And, of course, if you have health conditions, specific dietary needs, or a history of disordered eating, professional guidance is essential.

Final Thoughts

What I love about this new research is how it echoes that our minds are capable of more balance and adaptability than we often give them credit for.

We’ve built a culture that fears hunger, that fills every pause with snacks, screens and scrolling, when perhaps what we’re really craving is space.

If you read last week's blog on Okinawa: What Can We Learn From Blue Zones? then you may already be very familiar with the 80% rule (hara hachi bu), whereby we stop eating when we perceive our stomach to be 80% full, which is one of a list of factors that seem to contribute to a longer and happier lifespan in the five named places identified as having a high number of Centenarians (people who live past 100).

Maybe fasting, in its gentlest form, isn’t about deprivation at all. Maybe it’s about learning to sit in the quiet, trusting that the mind knows how to fuel itself from something deeper than what’s on our plate. It could be more to do with finding appropriate ways of calming the senses of anxiety or boredom that seem to come from skipping the odd meal.

If you'd like help recognising the signs of anxiety or addiction associated with consumption, you can reach out to Happy Citta for support: