Want better focus? Healthy cognition as you age? Or maybe just a better chess game? Then brain health is probably on your agenda.

Aside from cool sci-fi scenarios with a magic pill or technological plug-in that makes you a genius, how else can you improve and/or preserve your brain health?

Some promising research suggests that intermittent fasting can help you be healthier and happier, not just physically but mentally capable, well into old age. 

In this article, we’ll explore the science behind intermittent fasting for brain health.  

Ready for a brain health boost? Take the Simple quiz to gain access to a personalized fasting routine, insightful nutrition scores, and a supportive community. Your brain and wellness journey starts here!

The metabolic switch of fasting

To understand whether fasting can support brain health, it helps to understand how fasting works in the body.

There are many types of intermittent fasting. For more on types of fasting, please check out our article.

However, they all generally share a process that scientists informally call “flipping the metabolic switch.”[1] This occurs somewhere around 8–12 hours after your last meal, depending on several factors. 

With this switch, your body shifts from primarily using carbohydrate-based glycogen for energy to using stored fat from your fat tissues. This stored fat gets turned into substances called free fatty acids and then into ketones. 

Thus, you might know this state as being in ketosis.

Want to see your metabolic switch flip in real time? You can see when your body switches to “fat-burning mode” by checking the Metabolic Status indicator in the Simple app while fasting.

Your brain on ketosis: how fasting changes your brain

Why does the body do this metabolic switch into ketosis? Short answer: your brain.

Your brain isn’t that big — about 2% of your body size — but it needs a lot of energy to run relative to its size: about 20%–25% of your total daily calorie needs.[2,3] (Hey, being a genius takes fuel!)

Famines and food shortages were common for most of human history. Our brains needed to come up with a way to get fuel when food was scarce. Being smart, of course, it did: ketosis.

Ketosis occurs when our body makes ketones, or ketoacids, from fats or proteins. Ketones can provide energy when other fuels aren’t available. 

During fasting, ketones made from stored body fat become the brain’s preferred energy source. Not only do they provide energy, but they may also help regulate important factors in the brain.

Boosting neuroplasticity with BDNF

Two key players are BHB (β-hydroxybutyrate) and AcAc (acetoacetate). These ketones are made in your liver during fasting and are sent to your brain. In animal studies, they seem to boost brain-derived neurotrophic factors (BDNF).[4] 

BDNF helps create new brain cells, strengthens connections between them, and makes your brain more resilient to stress.

(By the way, BDNF is also stimulated by exercise. So perhaps a morning fasted walk might be a nice little brain boost!)

However, the research in humans isn’t as strong right now. The results vary, with some studies showing that fasting reduces BDNF.[5] Other factors like measurement methods, sex, and health status play a role. 

So, we need more human research to draw some better conclusions. But animal studies look promising.

Fasting and autophagy

Intermittent fasting also helps your brain through a process called autophagy.

Autophagy is the process your body uses to break down and clear out damaged cells to make space for new ones. In the brain, this can mean tidying up damaged cells and cellular waste products.

Brief periods of fasting enhance the activity of genes linked to autophagy.[6] This suggests that intermittent fasting could potentially have a positive impact on autophagic activity. But since we don’t currently have a good way to measure autophagy in humans,  we still can’t say for sure.

While good housekeeping is important in general, it’s likely especially important as we age. Just as some of us tend to accumulate clutter in our homes as we get older and acquire more “stuff,” our brains can do the same, building up cellular “gunk” that may diminish cognition or contribute to neurodegeneration.

So, fasting may also be part of healthy brain aging.

Fasting and neurodegeneration

Fasting is being explored as part of the treatment or prevention of many neurodegenerative diseases (i.e., diseases where brain or nervous system tissues break down or don’t work as well) due to its potential for enabling ketosis, among other physiological processes.[4,7]

For instance, evidence from research on Alzheimer’s disease suggests that fasting may help reduce the buildup of harmful brain plaques and slow down memory loss. 

Although we’re not entirely sure why this works, some think it’s because intermittent fasting could activate pathways that make brain cells tougher and fight inflammation.[7] However, research in this area is still in its infancy, so it’s too soon to explain exactly how this works.

For Parkinson’s disease, intermittent fasting might offer some protection, too. 

Some smaller studies have shown promising results with Parkinson’s patients on ketogenic diets, but we need much more research to say for sure.[8]

Fasting and insulin

High circulating insulin levels — which can lead to insulin resistance, a situation where cells can’t effectively respond to the signal of insulin — are increasingly linked to worse brain health.[9]

By lowering circulating insulin, fasting may help alleviate this and indirectly support brain health.[10] Exercise also helps support insulin sensitivity in the brain, so there’s one more vote for those nice little fasted strolls![11,12,13]

If you’re ready to give intermittent fasting a try, take our Simple quiz and start your fasting journey!

Will fasting make you smarter?

While there’s interesting evidence (mainly from animal studies) that fasting may slow neurodegenerative processes, it’s not clear whether it reliably boosts cognitive function in humans, especially neurotypical people (i.e., people with no diagnosed cognitive conditions or neurological variations).[14]

However, many people report feeling “sharper” when fasting. 

This is likely due to the release of catecholamine hormones such as adrenaline (epinephrine) and noradrenaline (norepinephrine), which are linked to alertness and focus.[15] 

On the other hand, other people report feeling “brain fog” with less focus and concentration.

Likely, there are individual variations in how fasting affects people’s cognitive performance, focus, and concentration. 

Take-home: Experiment and notice how you feel when you fast. 

• Do you feel more alert and focused? If so, then fasting may be a good fit for times when you need more mental horsepower.
• Do you feel fuzzy and foggy? If so, then perhaps time your fast, so you aren’t doing anything important during that period.

Will fasting make you happier?

What’s good for your brain (and the rest of your body) is good for your emotions, and intermittent fasting may also play a positive role here. 

Many people report feeling more energetic and positive while fasting.[15] In part, this may reflect the effects of dopamine, a neurotransmitter (brain chemical) involved in getting us motivated to seek rewards. 

In our evolutionary past, hunger motivated us to leave the safety of our burrows and go find food. The dopamine system is part of helping us take risks and get moving.[16] For some people, this activation of dopamine and surge of activity may help alleviate symptoms of depression.[17,18]

There’s also emerging evidence that fasting may play a role in helping alleviate some types of chronic pain, likely by working through some similar mechanisms, but research is in its infancy, and we look forward to seeing what may come out of this.[19,20]

Take-home: Try fasting out for yourself and observe how you feel during your fasts. Do you feel better? If so, great!