This article is for educational purposes only and does not replace the advice of a qualified healthcare or nutrition professional.
Fatigue is one of the most common reasons people seek help, and also one of the most frequently dismissed.
How many times have you mentioned feeling tired and been met with "well, you're busy" or "that's just life"?
Persistent low energy is not something you simply have to accept as the cost of a full life. It is your body's way of signalling that something needs attention, and it is worth taking seriously.
The challenge with fatigue is that it is a symptom with an enormous number of potential drivers. Sleep is the obvious one, but energy levels are influenced by nutrient status, blood sugar regulation, thyroid function, gut health, hormonal balance, stress, hydration, and more. This is why two people with the same complaint of exhaustion may need entirely different approaches.
Rule Out the Medical First
Before exploring nutrition and lifestyle, it is worth saying clearly: if you are experiencing persistent, unexplained fatigue that is not improving with rest, please speak to your GP. There are medical conditions that cause fatigue as a primary symptom, and they need to be identified or ruled out before assuming the answer lies in diet or lifestyle.
These include hypothyroidism (underactive thyroid), anemia, type 2 diabetes, coeliac disease, sleep apnoea, depression, chronic fatigue syndrome, and autoimmune conditions among others. A basic blood panel can check for many of the most common culprits, including iron, ferritin, B12, folate, vitamin D, thyroid function, and blood glucose. If you have not had bloods done recently and fatigue is ongoing, this is genuinely the most important first step.
Iron and Ferritin: The Most Common Nutritional Cause of Fatigue
Iron deficiency is the most widespread nutritional deficiency in the world, and fatigue is its most prominent symptom. Iron is essential for producing haemoglobin, the protein in red blood cells that carries oxygen around the body. When iron stores are low, less oxygen reaches your muscles and organs, and the result is a bone-deep tiredness that sleep does not fix.
Crucially, you do not need to be fully anaemic to feel the effects. Low ferritin (stored iron) without clinical anemia is extremely common, particularly in premenopausal women, and can cause significant fatigue, brain fog, breathlessness, and reduced exercise tolerance. Many people are told their iron levels are "normal" when their ferritin is in the low-normal range, which may still be insufficient for optimal function.
If fatigue is your main complaint and you menstruate, ferritin is worth checking specifically, not just a standard haemoglobin test.
Dietary sources of haem iron (most readily absorbed) include red meat, poultry, and fish. Non-haem iron sources include lentils, chickpeas, kidney beans, tofu, pumpkin seeds, fortified cereals, and dark leafy greens. Consuming non-haem iron alongside vitamin C significantly improves absorption, while tea, coffee, and calcium consumed at the same meal can inhibit it. If supplementation is needed, this should be guided by a healthcare provider based on your blood results.
Vitamin B12: Energy at the Cellular Level
Vitamin B12 is essential for red blood cell production, neurological function, and DNA synthesis. Deficiency develops slowly, often over years, but the symptoms when they arrive are significant: profound fatigue, weakness, brain fog, low mood, and tingling in the hands and feet.
B12 is found almost exclusively in animal products, making deficiency a genuine concern for those following vegan or largely plant-based diets without supplementation. However, deficiency also occurs in people who eat animal products regularly, particularly older adults, whose ability to absorb B12 from food declines with age due to reduced stomach acid production, and those taking metformin or long-term proton pump inhibitors, both of which impair B12 absorption.
If you are vegan or plant-based and not supplementing with B12, this is non-negotiable. A reliable daily supplement or regular intake of B12-fortified foods is essential. For everyone else, if fatigue is ongoing, getting B12 checked is worthwhile.
Vitamin D: More Than Just Bones
Vitamin D deficiency is extraordinarily common in the UK, with some estimates suggesting that around one in five adults has low levels. While vitamin D is most widely known for its role in bone health, it also plays a significant role in energy metabolism, immune function, and mood regulation.
Fatigue and low mood are among the most commonly reported symptoms of vitamin D deficiency, and research has found that correcting deficiency can meaningfully improve energy levels and general wellbeing. A daily supplement of 10 micrograms is recommended for the general UK population, and higher doses may be appropriate for those with confirmed deficiency.
Blood Sugar: The Rollercoaster Effect
If your energy tends to crash mid-morning, after lunch, or late afternoon, blood sugar fluctuations may be a significant driver. When you eat foods that cause a rapid rise in blood glucose, particularly refined carbohydrates and sugary foods eaten in isolation, the body responds with a sharp insulin release to bring blood sugar back down. This can overshoot, leaving blood sugar lower than before and triggering fatigue, irritability, difficulty concentrating, and cravings for more sugar or caffeine.
This cycle is extremely common and often misinterpreted as a need for more caffeine or sugar, which temporarily relieves the symptom but perpetuates the pattern.
Eating regular meals that include protein, fibre, and fat alongside carbohydrates helps slow glucose absorption and supports steadier energy throughout the day. Starting the day with a protein-containing breakfast rather than something purely carbohydrate-based is one of the most consistently helpful strategies. Avoiding long gaps between meals, particularly if you are prone to energy crashes, is also worth prioritising.
Thyroid Function and Iodine
The thyroid gland regulates metabolism throughout the body, and an underactive thyroid is one of the most common causes of persistent fatigue, particularly in women. Hypothyroidism is a medical diagnosis that requires treatment, but nutritional status can be relevant too.
Iodine is essential for thyroid hormone production, and deficiency has been re-emerging as a concern in the UK, particularly among those who avoid dairy and fish, which are the two main dietary sources in British diets.
Selenium is also needed for the conversion of thyroid hormones into their active form. Brazil nuts are an exceptionally rich source of selenium, with just two providing more than the daily requirement.
If you have symptoms of hypothyroidism including fatigue, feeling cold, weight changes, hair loss, dry skin, and low mood, thyroid function tests via your GP are an important step.
Dehydration: The Underrated Energy Drain
Even mild dehydration, as little as 1 to 2% of body weight, has been shown in research to impair cognitive function, reduce physical performance, and increase feelings of fatigue. The body is approximately 60% water, and virtually every physiological process, including energy production at the cellular level, depends on adequate hydration.
Many people are chronically mildly dehydrated without realising it, particularly those who work in heated or air-conditioned environments, or simply do not drink enough water throughout the day. Urine colour is a practical guide: pale straw yellow indicates good hydration, while dark yellow suggests you need more fluid.
Sleep: Quantity and Quality
This may seem obvious, but it is worth stating because sleep quality and sleep quantity are not the same thing.
You can spend eight hours in bed and still wake up exhausted if your sleep architecture is disrupted, meaning you are not getting sufficient deep sleep and REM sleep. Alcohol, caffeine consumed too late in the day, high stress, inconsistent sleep schedules, and sleep disorders like sleep apnoea can all fragment sleep quality even when total hours appear adequate.
Caffeine has a half-life of approximately five to six hours, meaning that a cup of coffee at 3pm still has half its caffeine content in your system at 8 or 9pm. For people who are sensitive to caffeine or who struggle with sleep quality, cutting off caffeine after midday can make a noticeable difference.
Stress and energy levels
Chronic stress is one of the most pervasive and underacknowledged drivers of fatigue. When the body is in a prolonged state of stress, cortisol remains chronically elevated, which over time dysregulates energy, disrupts sleep, depletes key nutrients including magnesium and B vitamins, and leaves you in a state of exhaustion that rest alone does not resolve.
This is not simply about relaxing more, though rest genuinely matters. It is about recognising that sustained psychological and physiological stress has real metabolic consequences, and that addressing it is not optional if energy recovery is the goal. This might involve working with a therapist, reassessing workload, improving sleep, or finding reliable ways to activate the parasympathetic nervous system through breathwork, movement, time in nature, or whatever genuinely helps you decompress.
In summary
Persistent low energy is not a character flaw, a productivity problem, or something to push through with more caffeine. It is a signal that deserves curiosity and investigation. The most common nutritional drivers include iron and ferritin deficiency, low B12, vitamin D deficiency, blood sugar dysregulation, and dehydration, all of which are identifiable and addressable.
Start with a blood panel if you have not already, eat regular, balanced meals, stay hydrated and protect your sleep and mental health.
References:
https://pubmed.ncbi.nlm.nih.gov/28625177/
VitaminB12-HealthProfessional
https://pmc.ncbi.nlm.nih.gov/articles/PMC10818509/
https://pmc.ncbi.nlm.nih.gov/articles/PMC1124000/
https://www.bda.uk.com/resource/iodine.html
https://pmc.ncbi.nlm.nih.gov/articles/PMC8579431/
