If you have been consistently tired for a while and sleeping is not fixing it, food is one of the more useful places to look. Not because it explains everything, but because nutritional gaps are one of the most common and most overlooked reasons people feel flat, foggy, and slow. Several of them are easy to address once you know what you are looking for.
This article covers the main nutritional reasons for persistent tiredness, what to eat more of, and when it is worth getting a blood test to check what is actually going on.
Iron: the most common culprit
Low iron is one of the most frequently missed reasons for chronic tiredness, particularly in women of reproductive age. Iron helps your red blood cells carry oxygen around your body. When levels are low, even everyday tasks can feel disproportionately effortful.
You do not need to be clinically anaemic to feel the effects. Low-normal iron stores can be enough to cause fatigue, poor concentration, and feeling cold more easily than usual. The only reliable way to know your levels is a blood test, which a GP can arrange.
Good food sources of iron include red meat, liver, dark leafy greens like spinach and kale, lentils, chickpeas, tofu, pumpkin seeds, and fortified cereals. When eating plant-based iron, pairing it with vitamin C (a squeeze of lemon, some peppers, tomatoes) increases how much your body absorbs. Tea and coffee, on the other hand, reduce iron absorption if drunk alongside or just after iron-rich meals.
Vitamin B12: the quiet deficiency
B12 is essential for nerve function and the production of red blood cells. A deficiency can cause deep fatigue, brain fog, and low mood. It develops slowly, which means people often do not notice until levels are significantly depleted.
B12 is found almost exclusively in animal products: meat, fish, dairy, and eggs. Vegetarians and vegans are at notably higher risk, as are older adults whose ability to absorb B12 from food tends to decline with age.
If your diet is plant-based or you have been vegetarian or vegan for several years, supplementation is usually the most reliable route. Again, a blood test is the best way to know where you actually stand before deciding how to address it.
Blood sugar: the afternoon wall
If your tiredness tends to hit at specific times, particularly mid-morning or mid-afternoon, blood sugar fluctuations may be part of the picture. Meals or snacks high in refined carbohydrates and low in protein, fat, or fibre cause a rapid rise in blood glucose followed by a drop that leaves you feeling flat and unfocused.
This is not a sign of diabetes or any medical condition in most cases. It is simply what happens when the macronutrient balance of a meal is off.
Eating regularly, and including protein and fat at each meal, is one of the most straightforward ways to keep energy steadier across the day.
Practical adjustments include adding protein (eggs, beans, meat, fish, dairy, nuts) and healthy fats (avocado, olive oil, oily fish) to meals that are currently mostly carbohydrate, and not going more than four to five hours without eating if your energy tends to crash.
Dehydration: surprisingly underestimated
Even mild dehydration, well before you feel thirsty, can affect concentration, mood, and energy. It is one of the simplest things to rule out and one of the most frequently overlooked.
Most adults in the UK need around 1.5 to 2 litres of fluid per day as a baseline, more if it is warm or you are physically active. Pale straw-coloured urine throughout the day is a reasonable indicator that you are reasonably well hydrated. Dark yellow or amber suggests you need more fluid.
Coffee and tea count toward your fluid intake, though they have a mild diuretic effect at high quantities. Plain water, herbal teas, and diluted fruit juice all contribute.
A quick check: what does your tiredness look like?
These questions can help point you toward which nutritional area is most worth looking at:
- Do you feel tired even after a full night of sleep?
- Do you feel the cold more than other people, or get breathless more easily than you would expect?
- Is your diet mostly plant-based, or have you not eaten much meat or fish for several years?
- Does your energy reliably crash at a specific time of day, particularly mid-morning or mid-afternoon?
- Do you skip meals, or go long stretches without eating?
- Do you drink fewer than six glasses of fluid a day?
- Have you had any blood tests in the last two years checking iron, B12, or vitamin D?
If several of these apply, a blood test to check iron, B12, vitamin D, and thyroid function is a sensible starting point. These are all routinely available through a GP.
When food is not enough
Nutrition is genuinely one piece of the energy picture, but it is not the only one. Sleep quality, stress levels, underlying health conditions, and medications all have a significant effect on how you feel day to day. Persistent tiredness that does not improve after a few weeks of dietary attention is worth discussing with a GP, particularly if it comes alongside other symptoms.
Food changes are worth making regardless, because they support everything else. But they are not a substitute for a proper assessment if something deeper is going on.
Persistent tiredness is often at least partly nutritional. The most common causes are low iron, low B12, unstable blood sugar, and mild dehydration.
Getting a blood test to check iron and B12 is the most reliable first step, especially if you eat a mostly plant-based diet or are a woman of reproductive age. In the meantime, eating regular meals with protein and fat, staying hydrated, and including iron-rich foods alongside vitamin C are all reasonable and low-risk adjustments.
If tiredness persists after a few weeks of change, or comes with other symptoms, it is worth seeing a GP to rule out other causes.
Questions people often ask
Good sources of iron include red meat, liver, dark leafy greens like spinach and kale, lentils, chickpeas, tofu, pumpkin seeds, and fortified cereals. Pairing plant-based iron sources with vitamin C (a squeeze of lemon or eating alongside peppers or tomatoes) increases how much your body absorbs.
B12 is found almost exclusively in animal products, so vegetarians and vegans are at higher risk of deficiency. Fortified foods such as plant milks, nutritional yeast, and some cereals contain B12, but supplementation is often the most reliable route. A GP or registered dietitian can advise on appropriate dosing.
It depends on the underlying cause. Blood sugar improvements from eating more regularly and including protein can be felt within days. Correcting a nutritional deficiency like iron or B12 typically takes weeks to months depending on severity. If you are supplementing under medical guidance, your GP may retest levels after a few months to check progress.
If you have been consistently tired for more than four weeks, or if tiredness is accompanied by other symptoms such as unexplained weight change, breathlessness, heart palpitations, or persistent low mood, it is worth seeing a GP. Fatigue can have many causes beyond nutrition, including thyroid issues, anaemia, sleep disorders, and other conditions that need proper assessment.
Yes, mild dehydration is a surprisingly common and often overlooked cause of fatigue. Even a small reduction in hydration can affect concentration and energy. For most adults in the UK, around 1.5 to 2 litres of fluid per day is a reasonable baseline, with more needed if you are active or the weather is warm.