What Causes Fatigue? Part 1: Diet, Sleep and Nutrient Deficiencies

What causes fatigue? A Bulletproof functional medicine perspective

Fatigue is one of the most commonly listed complaints that clients include on their pre-consultation questionnaire, so why are so many people so tired? One of the reasons that fatigue is so common is the poor diet and lifestyle choices that many people have, but there are also many other causes of fatigue which we will discuss in this article.

Where to start?

If you have not yet switched over to a Bulletproof style diet or one that focuses on eating real food with minimally processed foods then this is a good place to start. Eliminating processed foods, or the “Kryptonite” foods as Dave Asprey calls them is the first step.

This includes gluten, sugar, refined vegetable oils and basically most foods that come in a packet. As well as cutting out the processed foods you also need to focus on including plenty of good quality vegetables, some fruits, lean proteins and good fats.

One thing to watch out for if you are following a Bulletproof or low carb style of diet is to make sure that you are consuming enough calories during the day. Cutting the carbs and upping the protein can help to reduce your appetite, lose weight and in the short term feel great, but if you are not getting enough quality fats your diet may end up being too low in calories. A low-calorie diet will eventually lead to fatigue.

If you’re reading articles on the Bulletproof lifestyle, there is a good chance that you’re already focusing on a good diet, or at least know what you should be eating. So if you still don’t have the zest for life that you know you should, read on and we will explore some of the causes.

Optimal Sleep

This might sound obvious, but a lack of sleep or a lack of quality sleep will lead to being tired and lethargic during the day. Often people who are attracted to the Bulletproof diet are high performers who are implementing the diet and supplement hacks to get the most out of life, but sometimes that means sleeping less each night.

Everyone will get away with one or two nights of less sleep, and some people claim that they only need 5-6 hours a night, and while this may be true to survive, for most people who want to thrive they need around 7-8 hours of sleep a night.

Even missing out on one hour of sleep a night quickly adds up to missing out on an entire night’s sleep a week. There is a lot of research now that shows that poor sleep habits are going to affect not only physical and mental performance but also your health in so many other ways.

There are a lot of great articles out there on how to optimise your sleep but here are some steps that everyone would benefit from, whether you sleep well or not.

Have a regular night time routine that includes:

  • No screens for an hour before bed (or use blue light blockers)
  • Stick to a regular bedtime and morning wake time. If you’re a night owl, start to go to bed 30 minutes earlier each week
  • Write out a plan for the next day to help get the thoughts and “to do” lists out of your head
  • No caffeine after midday
  • Even you are still having trouble falling asleep, herbs and nutrients that can help include Passionflower, Zizyphus, Magnolia, Theanine and Magnesium

Rule Out Common Deficiencies

If you have optimised your diet and sleep and you are still having issues with fatigue, the next step is to rule out common nutrient imbalances. The two main nutrients that can cause fatigue are iron and B12.

The best way to assess iron levels is through a blood test, it is important to do iron studies which measures iron, ferritin (your iron stores) and iron saturation, I would also test hemoglobin to assess anaemia. Not only can too little iron cause fatigue but an excess of iron can also cause fatigue, the symptoms are similar and the only way to get an accurate diagnosis is to test.

Low B12 levels will also cause fatigue and this can be measured with a pathology test, the reference ranges for B12 in Australia ranges from 200-700, but the optimal B12 levels are above 500, so it is important not just to take the doctors word that everything is “ok.”

The best way to test B12 is by measuring methylmalonic acid. In Australia, at Planet Naturopath, we do this as part of the Organic Acids test. A blood test measures your B12 levels in the blood but the methylmalonic acid test measures how your cells are utilising B12 and is a much more sensitive marker of B12 levels.

Optimise Blood Sugar Levels

Low blood sugar or hypoglycaemia can cause fatigue, dizziness and mood changes, often this is caused by poor dietary habits with too many refined carbs, but even with switching to a high fat and moderate carb diet, hypoglycaemia symptoms can persist. Often small regular meals will help and things like intermittent fasting will exacerbate the symptoms, imbalances in your adrenal, thyroid and sex hormones can also make low blood sugar symptoms worse.

Another sign of low blood sugar can be waking in the middle of the night, a drop in blood sugar during the night will lead to a spike in your stress hormones, when this happens you are wide awake at 3 am. This poor sleep will only make daytime fatigue worse. Having an easily digested snack before going to bed can help in this situation, not a high sugar snack but something that includes some protein and good fats.

High blood sugar and insulin resistance can also cause fatigue, this is especially true when you get that sleepy feeling after eating a meal or if you find that you are always craving sugar or refined carbohydrates.

If you have insulin resistance, which is usually accompanied by excess weight you would be better off on a lower carbohydrates diet, intermittent fasting can be perfect in this situation. If you are having sleep issues it can be a good idea to include some quality carbohydrates in your evening meal.

Food Allergies

We have already talked about the importance of diet and how cutting out the common food triggers such as gluten, dairy and sugar can help to improve the symptoms of fatigue and optimise all aspects of health. While I don’t think everyone has to eat the “perfect” diet all of the time, if you are still consuming these foods some of the time I would experiment with a strict 30-day elimination diet where you cut out these foods 100% and then assess how you feel.

Even super healthy foods like eggs, nuts and seafood can be a problem for some people. This is less common, but you could be eating 100% Bulletproof and still be reacting to some of the foods in your diet. This is where food allergy testing can help, especially if there are other gut related symptoms, skin issues, headaches or “brain fog” which can all be caused by food allergies.

Histamine intolerance can also be a problem for some people, a Paleo or Bulletproof style of diet can be high in histamine-containing foods, and while this does not cause a problem for most people it can cause a range of symptoms in some people. High histamine symptoms include fatigue, especially mental fatigue, also allergy symptoms and anxiety are often present.

Salicylates are chemicals that naturally occur in many fruits and vegetables, they are particularly high when fruits are picked before they are ripe (which often happens with industrial farming practices). There is not test for salicylate sensitivity other than trialling a low salicylate diet to see if your symptoms resolve, it is a good idea to work with an experienced practitioner when doing special diets like a low histamine or low salicylate diet.

Symptoms of salicylate sensitivity are wide and varied, this makes it hard to diagnose by just assessing symptoms and a low sensitive diet is the best place to start. Fatigue, skin rashes, digestion problems, headaches and mood changes can all be associated with salicylate sensitivity.

What next?

There are different levels of fatigue, from the debilitating chronic fatigue where just getting through the day is a battle to milder forms where things are “just not quite right” and you know that you should have more energy.

Starting with optimising diet, sleep and assessing for common nutrient deficiencies is a good place to start but there are many other causes of fatigue that we will explore in Part 2.


At Planet Naturopath, we specialise in treating digestion and hormonal problems, as well as optimal athletic performance. We’re mainly localised to Australia, but open to everyone. If you need help improving your energy levels consultations are available via Skype or phone, consultations can be made via the website.

In Part 2 we will discuss adrenal dysfunction, thyroid problems, gut infections, methylation and mitochondrial dysfunction. These issues often cause more than mild fatigue symptoms and require specialised testing to get to the underlying cause.