A Functional Medicine Approach to Chronic Fatigue

If you’re reading this, there’s a good chance you’re exhausted, but not in the “I need a nap” kind of way. This is something deeper. A kind of bone-deep fatigue that doesn’t shift, no matter how much you rest or how early you go to bed.

You might wake feeling just as tired as when you went to sleep. Daily tasks feel heavier than they used to. Motivation comes and goes. And even the things you used to enjoy can feel like a struggle.

You may have already been to your GP, had standard blood tests, and been told “everything looks normal.” Maybe you’ve been offered antidepressants or told it’s just stress or burnout, but deep down, you know there’s something more going on.

This is the experience of many of my clients who come to me after months, sometimes years of searching for answers. They’ve tried the early nights, numerous supplements, random detoxes and more, but they’re still left wondering: Why am I so tired all the time?

In functional medicine, we don’t see fatigue as a vague or untreatable issue. We see it as a symptom, a signal that something within your body is out of sync.

Whether it’s a problem with your energy production at the cellular level, an overwhelmed nervous system, lingering effects from a viral infection, or blood sugar imbalances silently draining you, our goal is to uncover what’s really going on beneath the surface.

This article will walk you through how I approach chronic fatigue through a functional medicine lens: the possible root causes, the most useful lab tests, and the nutrition and lifestyle changes that can help you feel like yourself again, with more energy, clarity, and resilience.

What is Chronic Fatigue?

Chronic fatigue is more than just feeling tired, it’s a persistent, often debilitating sense of exhaustion that doesn’t improve with rest and significantly impacts daily life.

It can affect concentration, memory, mood, motivation, and physical stamina. For many people, even basic tasks can feel overwhelming.

Unlike occasional tiredness from a poor night’s sleep or a stressful week, chronic fatigue tends to persist for weeks, months, or even years. It can fluctuate in intensity, but there’s often a baseline feeling of “never feeling fully energised.”

Conventional Approach to Fatigue

In conventional medicine, fatigue is often seen as a secondary symptom, something to monitor while checking for more specific medical conditions. Your GP might screen for thyroid dysfunction, anaemia, or iron and B12 deficiencies, and if those come back normal, the conversation often ends there.

You may be told its stress, depression, burnout, or just part of getting older.

In some cases, a diagnosis like Chronic Fatigue Syndrome (CFS) or Myalgic Encephalomyelitis (ME) may be given, but treatment options remain limited, often focusing on symptom management, pacing, and psychological support.

This approach can leave many people feeling dismissed and disempowered, especially when their day-to-day experience clearly tells them that something isn’t right.

Common Root Causes of Chronic Fatigue: A Functional Medicine Perspective

Fatigue is often the result of several imbalances interacting beneath the surface.

In functional medicine, we rarely find just one root cause. Instead, chronic fatigue tends to emerge when multiple systems in the body, like the immune, metabolic, hormonal, and nervous systems are out of balance.

Below are some of the most common root contributors I explore when supporting someone with long-standing fatigue:

1. Mitochondrial Dysfunction

Mitochondria are the tiny “energy factories” inside your cells that produce ATP, your body’s energy currency. When they’re not functioning efficiently due to oxidative stress, toxins, or nutrient deficiencies, energy output drops, leaving you physically and mentally drained. This is often a key area of focus when fatigue feels “cellular” or is accompanied by muscle weakness and brain fog.

2. Blood Sugar Dysregulation

Large swings in blood glucose, driven by poor diet, stress, caffeine, or irregular eating patterns can cause both physical and mental fatigue. Highs may leave you jittery or anxious, while crashes lead to sluggishness, cravings, and brain fog. Insulin resistance can worsen this cycle and is often missed in standard blood tests, therefore more advanced tests for insulin resistance are usually recommended.

3. Chronic Infections or Immune Load

Low-grade viral reactivation (such as Epstein-Barr virus, herpes viruses, or even post-COVID changes), unresolved bacterial infections, or stealth pathogens can place an ongoing burden on the immune system, draining energy in the background. This is often relevant for those with fatigue that began after a viral illness or who experience regular immune flares or swollen glands.

4. Poor Sleep Quality or Circadian Disruption

It’s no surprise that poor sleep can cause fatigue, but even when sleep duration appears “normal,” issues like sleep apnoea, frequent waking, or disrupted circadian rhythm can all impair deep, restorative sleep. If you’re waking unrefreshed or feeling more awake late at night than during the day, your body clock may be misaligned.

5. Nutrient Deficiencies

Several nutrients are crucial for energy production, stress tolerance, and mitochondrial function. Common ones I assess include:

• Iron (particularly in menstruating females)
• Magnesium
• CoQ10
• B vitamins
• Zinc and selenium

Even if levels appear “within range,” suboptimal status can affect how well your body creates energy.

6. Hormonal Imbalances

Hormones help regulate metabolism, energy, and stress response. Fatigue may result from:

• Underactive thyroid (including subclinical hypothyroidism)
• HPA axis dysfunction (low cortisol or flattened daily rhythm)
• Low DHEA, testosterone, or oestrogen
• Perimenopausal or menopausal transitions in women

Testing adrenal, sex hormones and thyroid function appropriately, with a focus on optimal rather than just “normal” ranges is key in assessing this.

7. Gut Health Imbalances

Chronic fatigue often overlaps with digestive symptoms like bloating, IBS, or food sensitivities. An imbalanced gut microbiome, low-grade infections, or intestinal permeability (“leaky gut”) can contribute to systemic inflammation, poor nutrient absorption, and immune stress, all of which drain energy.

Functional Lab Testing and Assessment for Chronic Fatigue

When fatigue becomes persistent and unexplained, standard blood tests often don’t go far enough. Many clients I see have already had the basics checked, such as iron, thyroid function, or vitamin B12 and been told their results are “normal.”

But feeling constantly drained is not normal, and in functional medicine, we go deeper.

Here are some of the key assessments I may consider when investigating the root causes of chronic fatigue:

Mitochondrial and Energy Metabolism Markers

These help assess how efficiently your cells are producing energy:

• Organic Acids Test: Looks at metabolites involved in cell energy production. This can indicate poor carbohydrate or fat metabolism, thus impaired energy production, B-vitamin needs and oxidative stress.

Blood Sugar and Insulin Regulation

Even mild dysregulation can cause significant fatigue:

• Fasting insulin: Optimal 2–6 µIU/mL; conventional range 1.5–24.9
• HbA1c: Optimal <37 mmol/mol (<5.5%)
• Triglycerides and HDL ratio: High triglycerides and low HDL often signal insulin resistance

Thyroid Function

We often go beyond TSH to get a full picture:

• TSH: Optimal 1–2.5 mIU/L
• Free T4 and Free T3: To assess how well the thyroid is producing and converting hormones
• Thyroid antibodies (TPO, TgAb): To rule out or confirm autoimmune thyroid issues

Iron Status

Fatigue can be linked to iron deficiency — even without anaemia:

• Serum ferritin: Optimal range 40–100 µg/L in women, 50-130 µg/L in men
• Iron, transferrin saturation, and TIBC: For deeper insight into availability and absorption

B-Vitamins and Methylation

Assessing:

• Vitamin B12 and Folate
• Homocysteine: Elevated levels may suggest poor methylation or B vitamin insufficiency (optimal 6-10 µmol/L)

Adrenal and Cortisol Testing

To evaluate HPA axis function and daily cortisol rhythm:

• Salivary or urine cortisol assessments show whether cortisol is too low, too high, or dysregulated across the day

Inflammatory and Immune Markers

To screen for ongoing immune stress or inflammation:

• High sensitivity CRP (hs-CRP): Optimal <1.0 mg/L
• White cell count, ESR, ferritin

Comprehensive Stool Testing

If digestive symptoms or immune dysfunction are present, a GI test can uncover:

• Microbiome diversity and balance
• Parasites or pathogens
• Inflammatory/Immune activation markers like calprotectin or sIgA
• Short-chain fatty acid production and digestive efficiency

Nutrient & Toxin Testing

• Magnesium, CoQ10, zinc, selenium, vitamin D
• Heavy metals (mercury, lead, arsenic) or mycotoxin testing if relevant history or sensitivity is present

Sex Hormones

Sex hormone imbalances, particularly low oestrogen, progesterone, or testosterone can contribute to fatigue, low motivation, poor recovery, and disrupted sleep:

Hormone Tests to asses:

• Oestrogen, progesterone (especially in perimenopausal/menopausal women)
• Testosterone (in both men and women)
• DHEA, which plays a role in resilience and energy

Sex hormone imbalances are especially relevant when fatigue is accompanied by mood changes, poor exercise recovery, or changes in libido or menstrual cycles.

This testing framework helps identify which systems are under strain and where support is most needed. Functional medicine is not about guesswork, it’s about gathering the right data to guide a tailored, sustainable plan.

It’s not about running all these tests. A skilled Functional Medicine Practitioner can listen to and ask the right questions to determine what is most likely to be relevant and test from there.

All too often Functional Medicine Practitioners over test and leave themselves drowning in information, whilst causing additional financial strain for the patient.

The overuse of testing, then often lead to unnecessary complex supplement protocols, leaving an already overwhelmed individual more overwhelmed and feeling like they need to be dependant on supplements. This rarely leads to good long term outcomes.

A Functional Medicine Approach to Managing Chronic Fatigue

When it comes to resolving chronic fatigue, the most effective approach is rarely a single supplement or protocol. Instead, we work to uncover and correct the root causes, one layer at a time. In functional medicine, we view fatigue as a message from the body, a sign that energy production, recovery, or resilience is out of sync.

My goal is to create a personalised, achievable plan that restores energy by rebuilding the foundations of health while addressing your unique imbalances.

Here’s how we typically approach this.

1. Foundational Lifestyle Strategies

Before considering supplements or advanced protocols, we begin with the basics. These are the daily habits that either drain your energy or help restore it.

Nutrition

Food is fuel, but it’s also information that affects inflammation, hormones, and blood sugar. We start by:

• Appropriate management of refined sugars and ultra-processed foods that spike blood sugar and promote inflammation
• Increasing nutrient density with colourful vegetables, quality protein, healthy fats, and fibre
• Meeting optimal protein and caloric requirements
• Supporting mitochondrial health with foods rich in B-vitamins, magnesium, antioxidants, and CoQ10
• Tailoring intake to match energy needs and activity levels
• Addressing food sensitivities or intolerances that may trigger immune stress

Sleep

Chronic fatigue and poor sleep go hand in hand. We focus on:

• Building a consistent sleep-wake cycle
• Reducing blue light and stimulation in the evening
• Supporting melatonin production naturally through light exposure, appropriate evening and morning routines and meal timing
• Identifying underlying issues such as sleep apnoea, low blood sugar, or cortisol dysregulation that disturb sleep

Movement

It may seem counterintuitive, but structured, gentle movement helps restore energy, especially activity that helps to maintain muscle mass.

• Starting with low-intensity walks, yoga, or stretching, based on your capacity
• Avoiding overexertion and respecting energy limits (especially in post-viral or ME/CFS-type fatigue)
• Gradually building resilience with resistance training when tolerated

Stress Management and Nervous System Regulation

Unrelenting stress is one of the most overlooked drivers of fatigue. Strategies may include:

• Breathwork, journaling, or nature exposure regulate the nervous system
• Setting boundaries with digital devices, work, social media and stimulation
• Reviewing and helping to address the main drivers of stress. This may mean current stressors or even past traumas

2. Personalised Interventions Based on Testing

Once the foundations are in place, we use your lab data and history to shape the next steps. This is where functional medicine shines, offering precise interventions tailored to your biology.

Mitochondrial Support

If testing shows oxidative stress, poor energy metabolism, or nutrient deficiencies:

• Supplements like CoQ10, acetyl-L-carnitine, alpha-lipoic acid, magnesium, and B-complex vitamins may be introduced
• Support mitochondrial biogenesis and repair with polyphenol-rich foods and adequate protein

Hormonal Balance

Fatigue linked to hormone dysregulation (thyroid, adrenal, or sex hormones) is approached by:

• Rebalancing blood sugar and stress response
• Supporting HPA axis function with adaptogens (e.g., rhodiola, ashwagandha) where indicated
• Addressing low DHEA or testosterone with lifestyle, nutrition, and sometimes supplementation

Gut and Immune Support

If stool testing shows dysbiosis, leaky gut, or poor digestion:

• Addressing pathogens or imbalances using targeted antimicrobials
• Rebuilding the gut with probiotics, prebiotics, and gut-healing nutrients
• Reducing gut-derived inflammation and improving nutrient absorption

3. Natural Support Options (When Appropriate)

While not a replacement for lifestyle change, supplements can play a key role in energy restoration when selected based on need.

Some commonly used (and well-researched) options include:

• CoQ10: Essential for ATP production; often depleted in statin users or those with mitochondrial dysfunction
• Magnesium: Supports over 300 enzymatic reactions, including those involved in energy production and nervous system balance
• B-Vitamins (especially B12, B6, folate): Needed for mitochondrial function, methylation, and neurotransmitter balance
• Vitamin D: Low levels are linked to fatigue, low mood, and poor immune regulation
• Adaptogens: Ashwagandha, rhodiola, and holy basil can support adrenal function and mental stamina in those with chronic stress
• Omega-3s: Support cell membrane health, reduce inflammation, and benefit mood and cognition

Each supplement is considered based on your health status, lab findings, and overall plan. We use them to correct deficiencies, support weak systems, and speed recovery, but never as a standalone fix.

4. Monitoring Progress

Tracking is key to understanding what’s working and when to pivot.

I work with clients to monitor:

• Symptom changes (energy levels, sleep, brain fog, exercise tolerance)
• Functional lab markers over time
• Body composition or biometrics (if appropriate)
• Mental clarity, mood, and quality of life

We’re not looking for overnight fixes. The goal is sustainable, steady improvement based on a deep understanding of your body.

Conclusion: You Deserve to Feel Like Yourself Again

Chronic fatigue doesn’t just affect your energy; it affects how you show up in your life. It can rob you of your confidence, your relationships, your ability to work, and even your sense of identity.

When every day feels like you’re dragging yourself through mud, it’s easy to feel like you’ve tried everything and still aren’t getting answers.

But there is a way forward.

A functional medicine approach doesn’t promise a quick fix. Instead, it offers a deeper investigation into what your body is trying to tell you. It combines advanced testing with practical, real-world strategies tailored to your biology, your lifestyle, and your goals.

The result? A plan that makes sense and, most importantly, that works for you. If it is the right approach, thought out well, it should not make you feel more overwhelmed!

By addressing the root causes, whether that’s mitochondrial dysfunction, nutrient deficiencies, gut issues, hormonal imbalances, or nervous system overload we can help you build back your energy in a way that feels sustainable, not exhausting.

If you’re ready to take back control of your health and want expert guidance with a personalised, evidence-informed plan, I invite you to explore how we can support you through our Functional Medicine services.

👉 Visit my Functional Medicine page to learn more and book an initial consultation.

Let’s work together to help you feel like yourself again, with clarity, confidence, and energy to live the life you want.

References

1. Booth, N.E., Myhill, S. and McLaren-Howard, J. (2012) ‘Mitochondrial dysfunction and the pathophysiology of Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS)’, International Journal of Clinical and Experimental Medicine, 5(3), pp. 208–220.
2. Naviaux, R.K. et al. (2016) ‘Metabolic features of chronic fatigue syndrome’, Proceedings of the National Academy of Sciences, 113(37), pp. E5472–E5480.
3. Maes, M. and Twisk, F.N. (2010) ‘Chronic fatigue syndrome: Harvey and Wessely’s (bio)psychosocial model versus a bio (psychosocial) model based on inflammatory and oxidative and nitrosative stress pathways’, BMC Medicine, 8, p. 35.