How to prevent brain fog when fasting

I remember when I used to work, a certain colleague started to do fasting. We all knew about it in the office because he had informed us in quite excitedly tone had never gone on a fast prior to that time. And so, we counted the days along and helped him focus.

Then one day at the office, during our usual weekly meeting, it was his turn to give a progress report. He suddenly lost concentration and could no longer speak properly.

It took us a while to realize he was having some brain fog. You might have also experienced a sudden “blur” in your thoughts during fasting.

Consuming enough water and eating a wide range of foods to avoid malnutrition will help you avoid brain fog but also consider supplementing if you need to.

What is a brain fog?

Brain fog is a term used to describe a loss of memory or concentration. The Medical world describes brain fog as a set of symptoms ranging from forgetfulness to an inability to focus. Now, having a brain fog is usually seen as an indicator to another condition. Some other conditions, during or outside a fast, that can lead to brain fog these include;

  • Lack of Sleep: Sleep is important for the brain as it gives the brain “rest” and communicate with neurons within it. Also, during sleep, the brain cleanses itself and gets rid of unwanted substances. Basically, sleep enhances the longevity of the brain and an average adult is supposed to get at least 8 hours of sleep daily. Therefore, depriving yourself of sleep reduces your level of concentration and focus. Most times, you will find out that when you do not sleep well, you feel tired and “slow” throughout the day.
  • Age: An increase in age leads to a decrease in functions of certain parts of the body. So you would find that some elderly people find it harder to concentrate and remember certain information as well.
  • Hormonal imbalance: Certain hormones in the body help in cognitive function so when there is a low level of hormones produced in the body, one can experience brain fog.
  • Food: The way you eat can affect your brain function; some high carb foods are not healthy for the brain and can cause brain fog. It is advised that you eat healthy and include fruits and vegetables in your diet to help your brain function.

How to Fast successfully

There are different types of fasting, all with benefits. However, if you embark on a fast the wrong way, you might cause more harm to your body than good. Certain downsides of fasting can include ulcers, low blood sugar (hypoglycemia), etc. And like almost every other thing in life, there is a right way to fast. This involves certain things like:

  • Checking with your doctor if you have any health conditions. It is highly advised that you do not embark on a fast if you have any health conditions.
  • Have a scheduled time to fast and stick with it. Changing your fasting periods is like changing your sleep time; your body will have a hard time adjusting and this can cause issues with your internal clock.
  • When it is time to “break” your fast, start with water. Water neutralizes the stomach acids that would have been produced during the period of fasting and if you start eating without taking water first, the acids would work on the food faster and produce gases; safe to say, you would start to feel very uncomfortable shortly after you start eating if you don’t consume enough water.
  • Eat a broad spectrum of foods and eat healthy when “breaking” your fast. Eating large quantities of food is not a bad thing to do if you can handle it. Just a word of caution would be that you may get uncomfortably full by eating too much. Again, add whole grains as well as fruits and vegetables to your diet so that you can have the right amount of nutrients that your body needs to avoid brain fog.

Gradual approach to Fasting

Apart from the “why”, there is also a “how” to fasting. Fasting should not be abrupt, i.e. you just suddenly decide to stop eating without checking in with your physician. Fasting should be a gradual process. I am sure you want to know what I mean. But let me explain anyway.

A gradual approach to fasting is called Intermittent Fasting and this involves rotating between eating and fasting throughout the week. This method is a popular one in weight loss and has been shown to have a lot of benefits such as reduction in blood sugar and blood pressure.

Intermittent Fasting has different types, which include:

  • Choosing certain days in a week to fast. The popular one is called the Twice-a-week method, where you can choose 2 days in the week to fast.
  • Alternating the days, you fast, which basically involves fasting (or reducing your diet intake) on certain days, and continuing with the normal diet on the next day. However, research has shown that people who engaged in the “Alternate-Day-Fasting” method and stopped it had a significant increase in their cholesterol levels.

Using a Fasting Window, where you fast for certain hours of the day (a larger part of the day, between 14-16 hours daily), and eating for the remaining 8-10 hours of the day. The only challenge would be to find the appropriate window where you can fast.

  • Fasting for 24 hours at least once or twice a week, and then eating normally on the other days of the week when you are not fasting. The downside to this type of fast is that there are side effects like headaches, hunger, irritability and fatigue.

How Nutrition and Diet Affects Brain Fog

We have established that nutrition has an effect on the brain. The brain is constantly working, even when you are asleep. An organ that is constantly at work will also need a constant source of power, which can be supplied from foods containing vitamins, antioxidants and minerals. This is why the brain needs food.

But does nutrition also have an effect on brain fog? If you eat a lot of processed foods that are quite low in nutrients, it can lead to a lack of concentration and memory loss, also known as brain fog. Vitamin deficiency also leads to brain fog; insufficient vitamins like B6 and B12 can lead to confusion and memory loss.

Also, when glucose levels in the blood rise and fall sharply, you might start feeling dizzy all of a sudden. There are certain hormones as well that work closely with the brain (to regulate mood and appetite and brain function) that are produced in the gastrointestinal tract. A good example is Serotonin. So you see that you have to eat well and eat healthy to keep the brain working optimally and also to prevent brain fog.

If you are finding that you are eating a well balanced and healthy amount of fruits and vegetables you might want to consider supplementing with a good quality multivitamin as you may be lacking some micronutrients within your diet.

Studies have shown that micronutrients are lacking in certain crops

The following are what we recommend:

However, if you feel the you are getting enough micronutrients you might consider supplementing with a brain supplement like a nootropic

Are you properly hydrated when fasting?

There is a difference between being hydrated and being properly hydrated when fasting. It is important to note the difference as dehydration can also cause brain fog. A way to know if you are dehydrated is when you have headaches and begin to feel faint. To ensure that you are properly hydrated when you fast, you guessed right; drink water! This is important unless you are on a “dry” fast, which basically involves going without food and water, usually for religious reasons.

An average adult should consume at least 3 liters of water daily. If you are not properly hydrated, it will show in your urine (in addition to feeling dehydrated). If your urine is concentrated and is amber-colored, you need to take more water. The lighter your urine, the more hydrated you are!

Switching your brain’s fuel source from carbs to fat (The Keto diet)

When carbohydrates are broken down, it is turned to glucose and the brain uses a lot of glucose as a source of fuel. However, some people who consume less carbohydrates due to health reasons can consume foods that are high in fat. This is because the brain will also break down the fat into ketones. This consumption of foods low in carbohydrates and high in fat is called Keto diet. Studies have shown that Keto diets are effective in weight loss, reducing blood sugar and insulin, but are not suitable for those who want to build muscle mass.

A good way to switch from carbohydrates to fat is to drastically reduce carbohydrate intake and simultaneously increase the amount of fat in your diet. This way, your brain would switch from breaking down carbs in your body for fuel (as they aren’t much carbs in your system anymore) to breaking down fat. Welcome to the ketosis process, which is so called because the fats are broken down into ketones!

Can you function on a 24-hour or longer fast?

We have talked about different types of fasting; the kind where you can drink fluids while fasting and the other kind where you can go without both food and fluids during the fast. But it is important to know how your body functions before going on a fast, to avoid complications.

So, to answer your question; yes, you can go on a 24-hour fast or even longer. You would function well, but might feel hungry when it gets close to the time you normally have your meals. Then after a while, this hunger will reduce and eventually go away. This is quite normal.

What is not normal however is if you start to feel weak and this feeling does not go away. Once you start feeling weak, you should stop your fast. This is because you can have a brain fog or even more severe complications from your long fast, and that is dangerous, especially if you have/had an underlying medical condition.

Dieticians suggest that if you want to start a Keto diet, you can fast (by stopping your carbohydrates) for up to 36 hours or more and then start by infusing fat into your meals when you want to eat again. Remember, if you are taking medications, you should check with your doctor before embarking on any fast at all. Long term fasts are a great choice for losing weight; however, do not start a fast because you want to lose weight. It might look like a fancy idea, but you also need to know if your body can cope with fasting for longer periods.

Fasting Effects on the Brain

There are certain effects that fasting has on the brain and these include:

Cognitive Function

It has been shown that fasting, especially intermittent fasting can improve learning and resistance to stress because the neurons in the brain grow and communicate faster with themselves during this period. There are several studies to support this assertion.


This is the ability of the brain to keep learning new things continuously. Fasting helps the brain go through a period of “metabolic stretches” due to the change in diet and food and this makes the brain go into a conservation mode, thereby making your brain “sharper” during periods of fasting.

Physical effects of fasting

Studies have shown that fasting also has effects on the body, especially in the following major ways;

Improving the activity of Microorganisms on the Gastrointestinal tract

Fasting makes the microorganisms in the lining of your stomach work on the stored fat in your body to produce more energy. Microorganisms are therefore considered to be more active during fasting than at other times (Patterson et al., Intermittent Fasting and Human Metabolic Health).

Weight Loss and Lifestyle changes

Due to the fact that your body consumes the stored fat in order to function, you will realize that you will lose some weight. Also, if you enjoy late night snacking, fasting will help you reduce that habit because by the time you eat after fasting, you will feel full such that any other thing you eat will cause additional discomfort.

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