December 17


What Causes Brain Fog?


In this article I am going to talk about Brain fog. When I’m training my clients in Cardiff, brain fog is not explicitly mentioned all the time but the symptoms are certainly present when busy professionals are hard at it in their careers.

I’ll always remember one case a couple of years ago. A client starts with me at the same time she started a new job. With each week that passed my client looked increasingly strained.

The darkness under her eyes were becoming more defined and her ability to focus declined with each session we had.

When I would ask how everything was going my client would say “oh, I’m just having some trouble sleeping. Busy at work”.

There was no point doing high intensity exercise as it would have heightened the state of lethargy that was already there. Instead I opted to focus on mobility and body weight movement.

While my client never stated she had brain fog, the symptoms were there by the bucketload.

What is brain fog?

woman looking tired

Everyone gets tired at some point right? Even the extrovert at the party who won’t shut up. At some point they’ll run out of steam and have to take a lie down to recharge.

In your workplace there is likely someone who doesn’t stop all day. They keep going and wonder where all their energy comes from.

We all have increases and dips in energy over a 24 hour period known as the circadian rhythm and tend to function at our best in periods of 90 minutes known as the ultradian rhythm (1).

Periods of tiredness is normal, so brain fog must be something else entirely. Indeed it is and it starts with perception. Brain fog can be described as:

“Conscious perception of cognitive impairment and is related to mental fatigue” (2)

What separates brain fog from general tiredness is the perception you are experiencing something different from what you’d normally label as tiredness.

The idea of fatigue being in the mind stems from athletic performance, figure headed by Professor Tim Noakes (anyone into running will know him from being the author of the door-stopper ‘lore of running’).

Noakes theory is based on the Central Governor Model of Exercise Regulation which states that your brain is continually modifying the number of motor units used during a period of exercise.

If at any point, due to conscious (“This is getting hard”) and unconscious (heart beating) signals, your brain concludes it is reaching “homeostatic catastrophe” it will downregulate to ensure the duration and exercise stays within your physiological capacity (3).

Anyone who has done exercise will recognise you don’t suddenly find yourself in a pool of sweat crawling out the gym; we all have a threshold and experience tends to dictate how close we hover towards that threshold.

This is similar in terms of work performance. Brain fog is an individual perception of what you are experiencing. At the far end of that spectrum is a diagnosed condition known as chronic fatigue syndrome (CFS). This is defined as persistent physical & cognitive fatigue lasting longer than 6 months (4).

What are the symptoms of brain fog?

man looking confused

When thinking about the symptoms of brain fog, it is useful to pick apart the metaphor of ‘brain fog’ itself. If you go for a long walk and suddenly find yourself immersed in foggy surroundings, what would you be experiencing? Difficulty seeing out in front of you, confusion if you are going in the right direction, hesitancy about going forward.

This pretty much describes brain fog. When describing brain fog, sufferers of Chronic fatigue syndrome typically describe;

  • Confusion
  • Slowness in thinking and difficulty focussing
  • Lack of concentration and attention
  • Fatigue
  • Irritability

In one particular study featuring 138 Brain fog sufferers, they used the Wood Mental Fatigue Inventory test to help describe what they were experiencing.

The most common ways to describe brain fog were cloudy, forgetful and difficulty focussing and thinking. When asked about triggers for brain fog, the group reported the most, fatigue, lack of sleep, long periods of standing, dehydration and feeling faint (5).

How to reduce brain fog

Before discovering how to reduce brain fog it is important to recognise its completely natural to feel tired from time to time. Brain fog is more of a consistent sense of fatigue that plagues you both mentally and physically.

To reduce brain fog requires a systemic approach covering multiple areas. The main areas include Nutrition – State Control – Recovery Protocol.


healthy food

What you eat plays a large part in your energy levels. If the food you eat on a daily basis consistently influences low energy you can experience brain fog.

There are 2 areas covered which are blood sugar levels and stimulants.

1 Managing Blood sugar levels

cake stand

Every feel tired after lunch? Do you regularly get bouts where you feel everything is a slog. What could be happening is your blood sugar levels are going haywire.

If you ever see kids at a birthday party you will see an amplified effect of what regular bouts of sugar can do to your energy levels.

Yet, there is a side effect, which is the come down. The main offenders of rapidly elevating blood sugar levels are refined carbohydrates and sugary processed foods.

If, for example, you had a lunch consisting of a chicken sandwich, a pack of crisps and a can of coke (which is a fairly standard lunch), you would be consuming around 38.6g of sugar. The average recommended intake of sugar for an adult is 30g a day (6).

It is no wonder you would get a slump about an hour after your lunch with your body having to try so hard to transport the glucose (broken down form of sugar & carbohydrates) from the blood to its various storage units in the body.

Think about what you are eating consistently on a daily basis. When I train clients in Cardiff and online, rather than spoon feed them a meal plan, I aim to have them choose the food they eat from day one (there is long term habitual change reasons for this) but 3 criteria I mention is:

  • Favour complex carbs over refined
  • Increase your fruit & vegetable consumption consistent throughout the day
  • Keep protein levels high

The main reason for the first two (aside from the obvious nutrient benefits) is, if you are going to eat carbohydrates (which you should), make sure it contains fibre within it which will slow down the rate of digestion and absorption. This reduces the avalanche of sugar into your bloodstream in one go.

2 Stimulants


By far the biggest daily stimulant you are likely to encounter is caffeine. You are not alone, Caffeine is the most widely used stimulant in the world (7). There are a number of benefits to caffeine including memory enhancement (8), increased exercise efficiency (9) not to mention also reducing your chances of type 2 diabetes (10).

However, having spent some time working in call centres I’ve seen first hand the habit of consuming up to 10 cups of coffee a day. In healthy adults, caffeine has a half-life of around 5-6 hours (the time it takes for ½ the caffeine to be out of your system).

While no toxicity has been found with doses of caffeine between 300-500mg (11) (the average cup of coffee is around 95mg), there is relatively low danger from your daily cup of coffee.

What we are talking about is the effect the stimulant of caffeine has on you. If you are continually drinking caffeine throughout the day, considering the half-life is around 5-6 hours, means you will always have caffeine in your system throughout the day.

If you are experiencing brain fog, it is natural to reach for the daily pick-me-up. Yet, to reduce your experience of the dreaded fog may require you to have a longer gap between your caffeine hit in order to give your brain the chance to feel natural energy, i.e a system without stimulants.

One easy way of doing this is alternating coffee with caffeine-free options and herbal tea’s with are natural caffeine free.

State Control

As explained before, a large part of brain fog is the perception of mental fatigue. As a result the ability to control your state (mood) will play a large part in creating that perception.

The determinants of what influences brain fog can be condensed into 3 factors:

Your Mood

happy mood

In the Bio Psycho-social Model of pain, one of the factors that greatly increases an individual’s reporting of pain is their mood. If you have had recurring back issues, there is more chance of you feeling a tinge in your lower back if you take a dim view to a cold, dark winters morning.

Equally you may notice a lightening of back ache in a heat wave if you like nothing more than to feel the warm rays on your skin.

The ability to feel like you have control in your mood rather than be at the mercy of circumstance has long been a cornerstone of personal development. Part of being in control of your mood is a matter of attention and your internal dialogue (how you talk to yourself).

If your attention is focussed on factors you are unhappy with (raining instead of sunny, traffic delays instead of smooth journeys, endless emails instead of the work at hand) this will lead to your mood ripe for brain fog.

Equally, compile this with an internal dialogue that feeds into making your mood even worse. “It’s going to be one of those days”, “Im not feeling it today”, “Can this day get any slower”, your internal dialogue is a direct path to how you are feeling in the moment.

It is important to be aware that just because you think it doesn’t mean it’s true. The first step to changing your mood is changing your internal dialogue and what you are focusing your attention on.

Your Threshold

As brain fog is an evaluation of your current state, this will largely be determined by your threshold for what constitutes mental & physical fatigue.

An elite athlete on a daily basis has to cut out the feelings of exhaustion in order to continue training. This is not to say to use them as a benchmark but to recognise your threshold for fatigue is not binary. It’s a sliding scale where one persons “I’m tired” is another persons “I can focus on anything”.

Your Expectations

Imagine you experience lack of focus, mental fatigue, irritability and determine what you have is brain fog (or whatever name you call it). If you expect it to be a passing phase and likely to be gone within a few days, it is very likely you’ll work through it.

However, if you think this state is a consistent ongoing condition (perhaps even going to the doctor thinking its CFS), you’ll likely seek to manage it through adjusting what you feel you are capable of.

Expectations are usually based on what has happened before this moment. If you’ve never exercised before, your expectations of what you can manage in the gym are understandably different to a season gym user.

Yet, with my clients in Cardiff and online I always ask them to question and test their expectations to ensure they are congruent for their outcome rather than holding them back.

Recovery Protocol

So, you’re working 35-50 hour weeks and now you can’t think straight. To ensure brain fog doesn’t encroach further into your life, a way of recovering must be in place.

1 Sleep Quality


In a survey of over 11000 respondents they found 8 in 10 were unhappy (12) with the quality of their sleep. The respondents noted the top reasons for their sleep unrest was the sleep environment and stress/worry. Naturally, 3 in 5 said they experience sleepiness at least twice the following day.

It is as much of a no brainer as you are going to get in science; to have a clear head you need daily quality sleep.

Unfortunately, this isn’t happening. In a study featuring over 10,000 respondents (13), up to half were sleeping for less than 6.5 hours a night.

In this particular study it was agreed the optimal sleep duration is around 7-8 hours a night. This means a large share of people are sleeping sub-optimally, causing issues in memory, cognition and yes, brain fog.

If you are sleeping under 7 hours or you are unhappy with your sleep quality, it is imperative you work towards improving this.

World wide sleep expert Michael Walker in his book ‘Why We Sleep’ (14) set out a number of tips to help improve your sleep. These included:

  • Go to bed and wake up at the same time every day. This also includes weekends.
  • Keep your bedroom temperature cool. The recommended temperature is about 65”F/18”C for cooling your body towards sleep. Wear socks if your feet are cold.
  • An hour before bedtime, dim the lights and turn off all screens. Blackout curtains are helpful. Aim to cut all stimulation to a minimum.
  • If you can’t sleep, get out of bed and do something quiet and relaxing until the urge to sleep returns. Then go back to bed.

Although some can handle caffeine better than others, test avoiding caffeine after 1 p.m. and never go to bed tipsy. Alcohol is a sedative and sedation is not sleep. It also blocks your REM dream sleep, an important part of the sleep cycle.

2 Do low energy activities you enjoy

walk on beach

Low energy activities are those that you enjoy, make you laugh and/or gives you a sense of calm. These can include:

  • Meditation
  • Sauna & steam room
  • Massage
  • A Long walk on the beach
  • Watching a comedy show
  • Watching a movie
  • Meeting up with friends

All these activities require little energy and are low stress. They can put you in a mindset that strays further away from what fuels brain fog.

I would be hesitant to include rigorous exercise. Whilst exercise is very important and some use it as a period for thinking and stress reliever, exercise does pose a stressor on your body.

In a period where you are seeking recovery, an activity that also requires recovery is not.beneficial.

THIS IS NOT AN EXCUSE TO FORGO EXERCISE. When you feel brain fog is subsiding, resume exercise.


Brain fog can be an incredible hindrance to your work life and overall wellbeing. However, it doesn’t have to be a permanent state for you. Follow the right protocol and you can find that fog clearly as quickly as it forms.


  6. Institute of Medicine Staff and Institute of Medicine (US). Committee on Military Nutrition Research, 2001. Caffeine for the sustainment of mental task performance: formulations for military operations.

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brain fog, Psychology, sleep, stress

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