The term ‘fatigue’ is often used to describe extreme tiredness or exhaustion, resulting from mental or physical exertion or illness.

You could be suffering with chronic fatigue / Photo credit: Unsplash
You could be suffering with chronic fatigue / Photo credit: Unsplash

Fatigue can be classified as secondary, physiological, or chronic. Secondary fatigue is caused by an underlying medical condition or medication and generally lasts less than six months.

Physiological fatigue is caused by an imbalance in the routines of exercise, sleep, diet, or other activity. It is not caused by an underlying medical condition and is relieved with rest.

Chronic fatigue syndrome (CFS) is persistent or recurrent debilitating fatigue, that is not the result of ongoing exertion, or alleviated by rest, or explained by other conditions and results in a substantial reduction in activity.

Whilst secondary fatigue and CFS should be assessed by a medical practitioner, there are some physiological causes of fatigue that may be overcome by changes in our daily habits. Here are seven that you may not have known about.

Kim Plaza – Technical Advisor at Bio-Kult - explains the causes of your exhaustion.

What is causing you to feel so lethargic? / Photo credit: Unsplash
What is causing you to feel so lethargic? / Photo credit: Unsplash

Exercise induced fatigue

Although exercise may be an obvious thought when thinking about fatigue, it may not be obvious that changing up your routine may have an impact upon fatigue levels and adaptability. Exercise intensity, endurance, timing and type are all variables that cause different effects within the body systems. Physical exercise brings about a whole range of changes, affecting the biochemical equilibrium of the exercising muscle; including protons, lactate and free magnesium accumulation. Nutrients need to be supplied to this working muscle to restore chemical balance and adapt to the workout, meaning that energy stocks are depleted from elsewhere in the body. Inflammatory compounds are also released, which affects other organs, including the brain. Collectively, these mechanisms result in fatigue and can be seen as a debt that the body must restore in the form of rest. Chronic overtraining is described as the late stage of intense and prolonged training during which the exercise performance declines instead of becoming progressively better. It is therefore often mentioned that rest is as important as training. So, if you feel that your workout is getting much tougher than it used to be without changing anything, consider whether you’re overtraining. Many hypotheses about overtraining mention the involvement of inflammation, caused by a type of microtrauma. Supporting the stress response, that may have become dysregulated as a result of overtraining may allow us to overcome the physiological effects of exercise-induced fatigue. Rest is of course paramount as it allows the equilibrium of stress-related hormones to rebalance. Consider sufficient protein consumption as well as foods with high antioxidant content such as berries and grapes. Look after your gut, glutamine as well as fermented foods both have the potential ability to heal the gut lining and support the tight junctions that are important in modulating inflammation.

Lack of sufficient, quality sleep

Fatigue can be tricky to define, as it is a subjective experience. However, whilst everyone feels tired, sleepy or over-worked from time to time, it’s important to distinguish instances of temporary fatigue, which usually have an identifiable cause and a likely remedy, from on-going symptoms of unrelenting exhaustion, which are not relieved by rest.  For example, when we feel sleepy, it can stop us from doing our daily activities, which inevitably leads us to fall asleep. This type of sleepiness is often remedied by having a nap or a good night’s sleep. Fatigue on the other hand, is intensified by activity, at least in the short-term,7 with people often reporting a lack of energy, mental exhaustion, poor muscle endurance, delayed recovery after physical exertion, and nonrestorative sleep. Fatigue is therefore a more constant state of weariness, usually developing over time and can significantly reduce motivation and concentration as well as impact individual’s emotional and psychological well-being.


Changes in food intake and body composition seem to influence the symptoms of fatigue, possibly through the mechanisms of inflammation and/or dysregulation of energy cell metabolism (known as mitochondrial dysfunction). Undernutrition may result in weight loss and nutritional deficiencies leading to fatigue by means of ‘lack of energy’. When protein and energy intakes fail to meet a person’s need, body stores are broken down to provide energy, leading to the depletion of body fat and muscle, with consequent symptoms such as fatigue. There also appears to be a bi-directional association between undernutrition and fatigue. Whilst undernourished people are more prone to experience fatigue symptoms, fatigued people may be at risk of undernutrition due to lack of energy to prepare substantial meals.14

Poor gut health

Supporting a healthy microbial balance in the gut is also thought to be important for energy levels for numerous reasons. Beneficial species produce a variety of compounds, including B vitamins which are important for red blood cell formation (transporting oxygen around the body) and act as co-factors for energy production. Our gut bacteria also produce short-chain fatty acids (SCFAs) via intestinal fermentation of dietary fibre and resistant starch. SCFAs not only provide a fuel source for the cells of the gut lining, but also play an important role in maintaining overall energy levels. In fact, it has been estimated that SCFAs contribute to around 60–70% of the energy requirements of gut lining cells and 5–15% of the total caloric requirements of humans. Beneficial species also support the health of the gut barrier to reduce systemic inflammation, which is commonly associated with symptoms of fatigue. Finally, research is uncovering the important role that the gut microbiota play in mental and cognitive health via the microbiota-gut-brain axis. With fatigue being a common symptom in many psychiatric and neurodegenerative conditions. Supporting gut health may also have a positive effect on energy levels via this route. Therefore, try to consume a wide variety of plant-based foods containing plenty of prebiotic dietary fibre, resistant starches and polyphenols, to support microbial diversity in the gut, along with traditionally fermented foods such as live yoghurt, kefir, sauerkraut and kimchi.  Some may choose to supplement with live bacteria alongside fermented food, as some strains of bacteria have evidence of reducing tiredness, as well as supporting gut barrier function and producing SCFAs. Bio-Kult Boosted contains 14 different strains of live bacteria that were found to reduce tiredness and stress hormones. Bio-Kult Boosted also contains vitamin B12 which contributes to the reduction of tiredness and fatigue.

Dysregulated stress responses

In an acute phase, our bodies are well adapted to cope with stress. We get increased blood pressure, heart rate and cognitive function, while at the same time our digestive and immune systems are inhibited. Recovery from acute stress happens fairly rapidly, where hormone levels should normalise relatively quickly after an event. However, our bodies are not so well adapted to dealing with chronic stress, which can leave us with a host of potential problems. Chronic exposure to stress hormones has been shown to effect the area of the brain involved in memory processing and emotional regulation. It’s therefore perhaps unsurprising that common symptoms of stress include feeling anxious, low mood, difficulties sleeping, low energy, poor memory, lack of appetite, comfort eating, and cravings for stimulants or sugary foods (which are often symptoms associated with fatigue). Some people also notice a worsening of conditions such as irritable bowel syndrome or migraines. One study noted that stress and fatigue symptoms overlap, therefore reducing levels of stress would likely reduce symptoms of fatigue.

Unconducive environment

Taking note of our surroundings is vitally important as we interact with them on a minute-by-minute basis. The polyvagal theory discusses the impact our autonomic nervous system (which governs heart rate, blood pressure, metabolism, respiration etc.) has on prosocial behaviours. This theory suggests that a variety of influences (such as childhood experiences and social behaviours), shape our responses to new and existing environments resulting in positive or negative outcomes. For example, if an individual has had adverse childhood experiences, it is posited that their stress responses may be at an increased risk of dysregulation, which could predispose a person to stress-related conditions, including CFS. This is not to suggest that a person has a set chance of experiencing fatigue or CFS, however it may be useful to take note of your environment as well as people you socialise with. This could increase awareness of how these impact you on a daily basis.

Making small lifestyle changes could see promising results / Photo credit: Unsplash
Making small lifestyle changes could see promising results / Photo credit: Unsplash

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