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The 5 Most Common Causes of Fatigue

author avatar Dr. Eric Berg 08/31/2023

It’s normal to sometimes feel tired. But persistently feeling exhausted and having a constant lack of energy can indicate an underlying medical condition. 

Fatigue is a debilitating and disruptive symptom that can be caused by autoimmune diseases, sleep disorders, metabolic imbalances, poor diet, or chronic stress.

Let’s talk about fatigue symptoms and the common causes of chronic fatigue.

Daytime tiredness

What is fatigue?

Fatigue is a feeling of tiredness and exhaustion not relieved by rest or sleep. It's a common symptom linked to various medical conditions, such as anemia, chronic fatigue syndrome, heart disease, depression, and sleep apnea. 

Fatigue is also linked to lifestyle factors such as poor diet, lack of physical activity, insufficient sleep, and persistent stress. 

The symptoms of fatigue can vary depending on the underlying cause. Some common symptoms include: 

  • Feeling constantly tired, even after getting enough sleep

  • Lack of energy or motivation

  • Trouble concentrating 

  • Irritability or mood swings

  • Slow reactions and reflexes

  • Difficulty with memory and thinking

If you suspect an underlying medical condition may cause your fatigue, it's important to consult your doctor. A thorough physical examination, blood tests, and other medical tests can identify fatigue-related causes, including iron deficiency anemia, autoimmune disorders, or underactive thyroid function. 

While some conditions linked to fatigue can be diagnosed quickly, other causes of fatigue are less obvious, making it challenging to discover the root causes of persistent exhaustion. 

Here are three common causes of unexplained fatigue. 

Adrenal fatigue

Adrenal fatigue is a result of overworked or fatigued adrenal glands that can result in symptoms of fatigue. 

During stress, the adrenal glands produce adrenaline and cortisol. These stress hormones are important in regulating the stress response and are essential for hormonal balance and metabolism function—they also impact your blood sugar levels.  

Prolonged or chronic stress can cause the adrenal glands to become overworked and eventually burn out, leading to symptoms such as fatigue, blood sugar imbalances, and difficulty recovering from stress. Other symptoms associated with adrenal fatigue include sleep problems, mood swings, anxiety, and salt cravings. 

Fatigue written on papers

Chronic fatigue syndrome

Chronic fatigue syndrome (CFS) is a complex condition characterized by extreme and debilitating fatigue that doesn't appear to be connected to any underlying medical condition. 

According to research, the exact cause of CFS isn't well understood. It's suggested to result from a combination of factors, including disturbed sleeping patterns, viral infections, nervous system dysfunction, hormonal imbalances, and genetic predisposition.

Keto fatigue

Keto fatigue is a common symptom of transitioning to a ketogenic diet and typically diminishes within the first few weeks of going on keto. Also known as the keto flu, experiencing keto fatigue after starting a low-carb, high-fat diet is a normal response to the powerful changes in your metabolism. 

During the early stages of keto, your body shifts to burn fat instead of sugar for energy. Your brain, muscles, and organs must adapt to utilizing fats, and fatigue, lack of energy, and tiredness are hallmarks of this transition.   

Going keto can cause carbohydrate withdrawal, temporary electrolyte imbalances, and dehydration. It can also increase the need for B vitamins, all of which can trigger feelings of extreme fatigue.

The good news is that keto fatigue typically goes away after a week or two once your body adapts to keto. 

Watch the video below to learn more about the causes of fatigue. 

Common causes of fatigue

The human body is complex, and imbalances in one system can quickly impact overall physiological functioning, which can lead to fatigue. 

While fatigue can be a symptom of one specific underlying imbalance, it can also result from a combination of factors, making it challenging to diagnose its exact cause.  

Let’s look at five common causes of fatigue. 

1. Nutrient deficiencies

Lack of essential nutrients can disrupt energy metabolism, lead to hormonal imbalances, and can impact your sleep, all of which are risk factors for developing fatigue. 

Here are common nutrients needed for energy metabolism and restful sleep. 

Vitamin B12 and folate

Vitamin B12 and folate play a vital role in the production of energy. Both nutrients are needed to produce red blood cells, which carry oxygen to all the cells in the body. When your cells are well-oxygenated, they can produce energy more efficiently. 


Iron is a component of hemoglobin, a protein in red blood cells that binds to oxygen and carries it to all cells in the body, where it’s used to produce energy. Iron deficiency causes anemia, a medical condition characterized by severe fatigue and exhaustion. 

Vitamin B1

Vitamin B1 helps your metabolism convert fuel into energy, and vitamin B1 deficiency can quickly result in fatigue and lack of energy. 

A diet high in refined carbs and sugars depletes vitamin B1 stores, explaining why a poor diet can make you feel tired and drained.  

Magnesium and potassium 

Magnesium and potassium are closely linked to energy-making processes and are needed for restful sleep. 

Inadequate amounts of these minerals can increase the risk of sleep disturbances and imbalanced sleep cycles, causing fatigue and tiredness.   

Watch the video below to discover why nutrient deficiencies can cause fatigue. 

2. Stress

Stress can lead to fatigue by disrupting your physiological functioning, depleting nutrient reserves, and interfering with energy production. 

Cortisol is a critical component of the body's stress response. However, prolonged levels of elevated cortisol can impact your metabolism, cause imbalanced blood sugar levels, and may trigger sleep issues, all of which can lead to fatigue.  

Cortisol also profoundly impacts the brain. Research suggests that chronic stress can induce cognitive symptoms of fatigue, including brain fog, trouble concentrating, and poor memory function.   

3. Poor sleep

Poor sleep is a significant risk factor for fatigue. Sleep issues disrupt the body's ability to regulate energy levels and can cause hormonal imbalances linked to tiredness and exhaustion. 

In addition, poor sleep can also contribute to other factors that cause fatigue, such as decreased immune function, weight gain, and depression, all of which can worsen fatigue and reduce overall well-being.

4. Thyroid

An underactive thyroid gland is a common reason for fatigue. 

Thyroid hormones are a key metabolic regulator and disrupted thyroid function slows down all aspects of energy production. This can lead to symptoms including fatigue, weakness, and lack of energy.

5. Low stomach acid 

Stomach acid is needed for protein digestion, absorbing vitamins and minerals, and protecting the digestive tract from microbes.

Low stomach acid, or hypochlorhydria, is a prevalent condition that typically affects people aged 50 and older. Lack of adequate stomach acid can result in iron and vitamin B12 deficiencies, resulting in anemia and fatigue. 

Person with fatigue trying to recharge 

Key takeaways

Fatigue is characterized by debilitating tiredness and persistent exhaustion. It’s a common symptom linked to various causes, including underlying medical conditions, medication use, and hormonal imbalances.

In addition, lifestyle habits, including poor diet, lack of regular exercise, and poor sleep, can cause or amplify fatigue. 

Ruling out medical causes, making appropriate dietary changes, and focusing on healthy sleep are the first steps to address and combat fatigue, tiredness, and persistent lack of energy.    



1. What are the warning signs of fatigue?

Fatigue is a common symptom that can have many different causes. Some warning signs of fatigue include persistent tiredness and lack of energy, difficulty concentrating, weakness, depression, lack of motivation, and problems with memory function. 

2. What are the common types of fatigue?

Some common types of fatigue include adrenal fatigue, chronic fatigue syndrome, keto fatigue, or pathological fatigue caused by an underlying medical condition such as autoimmune disease, infection, depression, or heart disease. 

Fatigue can also be a side effect of certain medications, including blood pressure medications, antihistamines, and other drugs. 

3. Why am I tired and have no energy?

There are many possible causes of feeling tired and having no energy. Sleep problems, chronic stress, poor diet, and lack of physical activity are all common causes of tiredness.

Fatigue can also be a symptom of potential medical conditions, including anemia, diabetes, depression, and hypothyroidism. 

4. When should you worry about fatigue?

Fatigue can have many different causes, some of which may be serious and require medical attention, and others may be due to lifestyle habits, sleep disturbances, or poor diet. 

If you have unexplained and persistent fatigue that isn’t relieved by a good night's sleep, it's best to consult your healthcare provider to identify potential underlying causes and explore appropriate treatment options. 

5. Can keto and intermittent fasting cause fatigue?

Yes, transitioning to a ketogenic diet can cause fatigue, tiredness, and lack of energy. Keto fatigue is a temporary symptom due to your body adjusting to burning fat instead of sugar as an energy source. 

Similarly, even though it has a lot of interesting health benefits, intermittent fasting can cause fatigue. Starting intermittent fasting disrupts your usual eating patterns, causes hormonal changes, and can trigger cravings, all of which can result in experiencing fatigue and low energy. 

6. What are the best ways to combat keto fatigue?

To combat keto fatigue, it's essential to stay hydrated, add electrolytes to your keto regime, eat plenty of nutritious foods on the keto food list, and avoid vigorous physical activity until your body has fully adapted to keto.   

Doing Healthy Keto® is an excellent choice to fight keto fatigue. Healthy Keto focuses on nutrient-rich, high-quality keto foods and helps your body to get plenty of electrolytes and B vitamins needed to curb fatigue and tiredness. 

7. How can I get rid of fatigue?

How to get rid of fatigue depends on its underlying cause. However, some general tips may help alleviate fatigue, including getting enough sleep, avoiding carbs and sugar, getting regular exercise, and finding relaxation techniques to combat stress. 

If you experience unexplained fatigue, consult your doctor to identify possible medical concerns or medications that may cause your persistent tiredness and lack of energy.

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