Does skipping meals sharpen your mind?

The pros and cons of not eating

Mar 02, 2025

I decided to kick off this series of articles about eating and how it affects your brain in a slightly odd place: what happens if you don't eat? Obviously if you go without food for long enough, you'll die, which clearly has a very negative effect on your brain health. I think we can all agree that’s best avoided.

However, intermittent fasting, caloric restriction, and various similar diets are widely recommended for weight loss, longevity, and various other reasons. They’re nothing new: people have been fasting for centuries. Hippocrates often recommended fasting as a therapeutic tool for illnesses, while Cicero and Marcus Aurelius believed that eating more than one meal a day was unhealthy and gluttonous. Ayurvedic practice involves regular fasts, and fasting is also practiced by Christians, Muslims, Jains, Buddhists, and many others.

Popular fasting techniques include the following:

16/8 Method (also known as Lean-Gains): fast for 16 hours each day and eat only during the other 8. This is not dissimilar to what Muslims do during Ramadan.
The Warrior Diet: a more extreme version of 16/8, fasting for 20 hours each day and eating a large meal at night.
One Meal A Day (OMAD): basically, what it says.
5:2 Diet: eat normally five days a week and restrict calorie intake to around 500-600 calories for the other two days (not consecutive)
Eat-Stop-Eat: a 24-hour fast once or twice a week.
Alternate-Day fasting: fast every other day. Some people choose to eat a few calories on fasts, while others prefer to go without food completely.

Weight loss, however, is not my area of expertise or interest. What I’m much more intrigued by is what effect intermittent fasting has on your brain.

Before I go any further, fasting is not recommended for everyone. Don’t try it without medical supervision if you have (or think you may have or are at risk of) diabetes, hypertension, eating disorders, heart issues or if you’re pregnant, underweight or taking medication.

Getting hangry: the short-term effects of hunger

For the most part, your brain and body likes regular routines. Your Circadian rhythms operate on a 24-hour cycle to determine when you should eat, when you should sleep, when you're most mentally active, and so on, and it functions best if you stick fairly closely to that cycle. In the West, most of us eat three times a day, and our bodies have adapted to that.1 Intermittent fasting would appear to disrupt that cycle: your brain isn't getting the energy it expects when it expects it.

As Dr Mark Mattson of the School of Neurology at Johns Hopkins University points out, we can survive and function perfectly well without food for quite some time. Animals, including humans, “evolved so that their bodies and brains were able to function very well, perhaps optimally in a food-deprived state. Otherwise, they wouldn't have been successful in acquiring food.”2 Clearly, then, skipping a few meals is highly unlikely to have major adverse effects.

However, as you’re probably aware, hunger does have a noticeable and immediate effect on your mind. We’ve all experienced the feeling of being hangry: if food is just a couple of hours late, we quickly become irritable, grumpy, and sullen. Alongside that, we get the feeling of "brain fog”, where we just can’t think clearly, and we start to feel tired, sluggish and unmotivated. We may get headaches, dizziness and nausea, and we begin to feel stressed and anxious.

All these are symptoms of the body switching modes to reduce energy consumption as glucose levels drop. It’s preparing to burn stored fats and ketones, a metabolic switch that happens after about 12-16 hours. This is why most fasting regimes involve going without food for at least 16 hours - that’s how longs it take to fully trigger the metabolic switch and start the process of ketogenesis.

This mode switch causes changes in the production of multiple hormones, which can have wide-ranging effects on your body and brain. These effects can be exacerbated if electrolyte levels drop, which is common if you don’t drink enough while fasting. Once the process of ketosis begins, and your brain is getting sufficient energy from ketones, things start to get back to normal - for a while, at least. You can only go so long powered by stored fats before you have to eat actual food again.

In other words, your body doesn’t like being deprived of its regular intake of food. It’ll cope just fine by using alternative energy sources, but don’t be surprised if it protests about having to do it.

Potential long-term benefits of fasting

However, if you can get through these short-term setbacks, it seems that fasting may well have some very positive long-term effects.3 It’s essential to note two things, though: not all studies confirm these effects,4 and results seem to depend on both the individual and the specific fasting pattern.5 It is not possible to say with any reliability that this pattern is better or worse than any other, or which one will work for you - if any of them.

That said, there appears to be good evidence for the following:

Improved cognitive function: improved learning, memory, alertness, and executive function.6 After a few months, the effects are noticeable in a significant proportion of people, particularly older people.7
Neurogenesis: may promote the growth of new neurons in the hippocampus, which is associated with learning and memory.8 It also triggers production of brain-derived neurotrophic factor (BDNF), a protein essential for brain health.9
Neurological disease resistance: ketones have naturally anti-inflammatory properties which can potentially help the brain resist oxidative stress and reduce the risk of developing brain disorders. For example, can improve response to chemotherapy, enhance functional recovery after a stroke, and reduce the severity of epilepsy, Alzheimer’s, Parkinson’s, and MS.10 Some studies also suggest that it can benefit autism sufferers.11
Promotes autophagy: this is a process where cells break down accumulated waste, recycling usable parts into functional cell components and removing the rest. This reduces protein buildup in the brain, protects existing neurons, and allows new neural connections to develop.12

What this suggests is that when it comes to brain health, when you eat is possibly as important and what you eat and how much you eat. Intermittent fasting may have numerous benefits. However, it’s not for everyone, and it can be a pretty unenjoyable process, for yourself and for everyone around you.

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