Nutritionist Sarah Di Lorenzo: The most common reasons why you are feeling fatigued

Fatigue is the most common complaint I hear in my clinic.

I am not talking about occasional tiredness after a big week or a big night out but the kind of persistent exhaustion that follows you from the moment you wake up and through the day, just making everything that much harder.

This is the kind of fatigue that coffee does not fix, that weekend sleep ins can’t resolve and sadly that people have learned to accept as just the way life feels.

This is not normal and in the majority of cases I see, it is entirely reversible.

So I am going to share what I see as the most common clinical reasons I find behind persistent fatigue and offer you the solution of what to do about each one.

Starting with lack of protein. This is the first thing I assess and the most frequently overlooked driver of fatigue I see.

Protein provides the amino acid precursors for serotonin, dopamine, and noradrenaline which are the neurotransmitters that regulate energy, motivation and mental clarity.

Protein also stabilises blood sugar between meals, preventing the energy crashes that most people blame on carbohydrates when the real culprit is inadequate protein at the previous meal.

A key tell-tale sign is if you are reaching for coffee or sugar at 3pm every single afternoon, your protein intake at breakfast or lunch is probably not enough.

Aim for 1.2g–1.6g of protein per kilogram of body weight daily and distribute it across every meal.

Another reason I see people fatigued is because blood sugar is dysregulated.

The energy rollercoaster of a high after a meal, crashing an hour later, craving sugar to get back up is one of the most common and most fixable causes of fatigue I see clinically.

What drives this is eating meals high in refined carbohydrates, high glycaemic index and low in fibre, protein, and healthy fats that cause rapid blood glucose spikes followed by equally rapid crashes.

The solution is definitely not to eat less which many do, the solution is to eat differently.

Always pair carbohydrates with protein, fat, and fibre.

Eat protein and vegetables before carbohydrates at meals and go for a 10 minute walk after meals.

These simple changes produce dramatic improvements in sustained energy within days.

Something so often overlooked is the possibility of iron deficiency.

I always tell my patients to get their blood tests done annually to keep an eye on general health.

Iron deficiency even without full anaemia is one of the most common and most missed causes of fatigue, particularly in women.

We need iron, it is essential for haemoglobin production which is the molecule that carries oxygen to every cell in your body.

Without enough iron your cells are essentially running on reduced oxygen supply, producing the deep, persistent exhaustion that no amount of sleep resolves.

The best dietary sources of iron include red meat, legumes, leafy greens, and pumpkin seeds.

Always remember to pair plant-based iron with vitamin C to dramatically improve absorption and always get your ferritin level tested, not just haemoglobin, because ferritin can be significantly depleted long before anaemia appears on a standard blood test.

Other minerals and vitamins linked to low energy are Vitamin D, Vitamin B12 and Magnesium.

These are the most common nutritional deficiencies we see in Australia and all three produce fatigue as a primary symptom.

Vitamin D receptors are present in virtually every cell in the body and low levels are consistently associated with fatigue, low mood, poor immune function and excess weight.

Vitamin B12 is essential for neurological function and red blood cell production.

Deficiency of B12 is profound exhaustion and cognitive fog, particularly in people eating plant forward diets, this is where I strongly recommend supplementing to all my patients.

Magnesium is involved in more than 300 enzymatic reactions in the body including ATP energy production so without it your cells literally cannot produce energy efficiently.

Get all three tested and address deficiencies through food first by looking at your intake of foods such as oily fish, eggs, leafy greens, legumes, nuts, and seeds and I always recommend supplementation where genuinely needed.

Poor gut health is a connection that most people miss entirely, they would not even think it could be a possibility.

The gut microbiome produces a significant proportion of the body’s serotonin and directly influences energy, mood, and cognitive clarity through the gut-brain axis.

Chronic gut dysbiosis which is an imbalanced, depleted microbiome driven by low fibre intake, carnivore diets, ultra-processed foods, and inadequate plant diversity would have to be one of the most under appreciated drivers of persistent fatigue I see in clinical practice.

We need a diverse, fibre-rich diet with thirty or more plant foods per week, regular fermented foods, and significantly reduce and ideally avoid most ultra-processed foods. When this is addressed people see better energy within four to six weeks.

The gut-energy connection is very real, it is measurable, and it is one of the most powerful levers available for addressing chronic fatigue through food.

I do feel this is very obvious but something I need to address — sleep. Most people know that not enough sleep causes fatigue. What is less well understood is that poor quality sleep, even seven to nine hours of fragmented, non-restorative sleep can produce identical exhaustion. I always encourage my patients to try and understand the quality of their sleep, not just the duration and what could be keeping them awake at night.

Sleep apnoea, blood sugar dysregulation overnight, magnesium deficiency, alcohol and chronic stress all disrupt sleep architecture without necessarily reducing total hours.

If you are sleeping eight hours and waking exhausted, the quality of your sleep deserves as much attention as the quantity.

I do often suggest a magnesium glycinate supplement taken before bed, trying to get a consistent sleep schedule, removal of screens an hour before sleep, last meal three hours before bed, clean sleep environment and a healthy evening meal that prevents blood sugar drops overnight.

All of this really can improve sleep quality and therefore daytime energy.

Dehydration and post‑viral load are other possible causes that both drive fatigue, but for slightly different reasons that add up.

When you’re dehydrated, your blood volume drops, so your heart has to work harder to circulate oxygen and nutrients and your blood pressure is more likely to dip when you stand. That reduced perfusion to muscles and brain feels like heaviness, weakness and “foggy” tiredness.

At the same time, after you could have had a virus and been sick your immune system is still active and clearing debris, using a lot of energy and releasing inflammatory cytokines that directly signal the brain to rest and reduce activity.

Put together, you have less efficient circulation plus an ongoing inflammatory “sickness response”, so even small tasks can feel disproportionately exhausting until fluids, electrolytes and recovery have caught up.

Something I tell all my patients is that persistent fatigue is not a personality trait and it is not something you simply have to live with.

In the majority of cases it has a nutritional, hormonal or a lifestyle driver that can be addressed with the right approach.

The best place to start is with blood tests including ferritin, vitamin D, B12, thyroid function, and fasting blood glucose.

Then look at your diet, check protein adequacy, fibre diversity, blood sugar regulation, and gut health.

In my clinical experience these two steps alone identify the cause for most of the chronically fatigued patients I see and taking the time and effort addressing them produces results that genuinely change people’s lives.