Food is not just Fuel


A very common saying I hear from people when they discuss nutrition is “Food is our fuel so it’s important we get the right stuff in to fuel the engine”. While this has some relevance, it is only part of the story and it overshadows the important role food plays in terms of the actual metabolic and physiological processes that govern our health and fitness (i.e. not just “fuelling”). Thus, if an athlete simply focuses on the energy content of what they eat to ensure they are fuelled, they are likely to miss out on the other functional requirements performed by certain foods which arguably have more of an overall bearing on how well you perform. Let me explain:

Different Fuels, Different Energy Pathways?

Do we just have one energy system? Is carbohydrate the only food we can produce energy from? The answer to both of these questions is no. We have several energy systems and there are several ways in which we can produce energy other than using carbohydrates. We can produce energy from fatty acids and amino acids. We can even recycle lactate and other intermediates to produce glucose. Being fuel efficient means tapping into these different systems and making the body more adapted to burning other sources of fuel other than carbohydrate. This then improves your overall fitness by making you more fuel efficient and increasing the number of pathways by which you can produce energy. What you eat can govern what energy system you use and hence, not use. Put simply, if you eat mainly carbohydrate then your body will solely rely on carbohydrate as its predominant fuel source. The trick is to vary what you eat and the amounts of different foods you eat so that you switch on as many pathways as possible. The most important and valuable pathway to switch on is your fat burning system particularly for long distance events. This is what’s known as “Fat Adaptation”.

Training Adaptations

The body improves its fitness through the adaptations that take place in response to training. Endurance training results in mitochondrial biogensis and capillarization. Speed training results in improved lactate buffering capacity while strength training increases muscle fibre growth. All of these adaptations require certain nutrients. For example, Leucine is an essential amino acid which is needed to trigger protein synthesis which can be found in high amounts in meats and eggs. Protein synthesis is the process used to make new mitochondria and new muscle fibres. Thus, choosing the types of food you eat and not just looking at its energy content is crucial if you want to reap the rewards of your training. An quick example to consider would that eating some chicken or eggs post training is more likely to improve your training adaptations than a bowl of pasta with a piece of bread.


One of the eternal struggles of an athlete is fighting off flu’s and colds. Heavy exercise suppresses the immune system and the first few hours post training is when athletes are at particular risk of picking up an infection. The relationship between exercise and immunity can be described as a u-shaped curve. No exercise weakens immunity, moderate exercise improves it and chronic exercise weakens it the most. Many people simply train too much and are thus frequently are fighting illness and feeling run down. Nutrition can play a big role here in terms of enhancing the immune response and reducing the inflammation and stress caused by heavy exercise. Eating foods which have high antioxidant content such as berries, peppers and other colourful fruits and vegetables helps strengthen the immune system. Omega 3 fats found in oily fish are known to have an anti-inflammatory effect whereas other foods such are refined vegetable oils are known to have pro-inflammatory effects. Therefore choosing foods such as salmon and mackerel while avoiding foods like spreadable butters and biscuits can help to bring down the inflammation and prevent illness. Another important area of the immune system is the digestive tract in particular the intestines where the gut bacteria are housed. Many infections occur here when the probiotic bacteria are overrun by unfriendly bacteria. Eating foods rich in probiotics such as natural yoghurts and other fermented diary foods can help boost the good bacteria and prevent infection. My point here is that you can still train hard and not get sick if you get your nutrition right.

Hormonal Control

Every bodily function is controlled by chemical messengers known as hormones. There are hormones which govern everything from our metabolic rate to appetite to sleep.  Carbohydrates, proteins and fats can switch certain hormones on and affect their response. One of the most important interactions between food and hormones is carbohydrate and insulin. High carbohydrate foods cause a rapid and large release of insulin. Insulin has several functions but its main responsibility is to store carbohydrates (as well as protein and fat). As storage is not something ideally you want occurring on a constant basis, choosing how much and when you eat a large carbohydrate meal is an important consideration. There are many other hormones that are affected by food such as Growth Hormone (triggered by protein and affects growth and repair), Leptin (triggered by carbohydrate and affects metabolism and appetite), and Testosterone (triggered by fats and affects muscle growth). Understanding the relationship between foods and hormonal response is essential the essence of nutrition. Understanding this interaction tells us exactly how food governs our health.


After training and nutrition, sleep is arguably the next most important factor that governs your health and fitness; in fact, some say it might even be top of the list. The reason is that there are certain hormonal responses that occur while we sleep that dictate our metabolism, appetite, cell growth and repair, mood and immune function. This controlled by certain hormones such as growth hormone and cortisol. During sleep, it is desirable to have high growth hormone release and low cortisol response. What you eat before bedtime can affect the levels of these hormones as protein is known to raise GH while high sugars are known to raise cortisol. Therefore choosing a low sugar protein food such as cottage cheese or natural yoghurt with some mixed nuts can help to raise GH while keeping cortisol low. This can help to improve sleep, improve recovery and ensure that stress levels are controlled during the rest of the day.

Cognitive Function/Mood State

There is a saying which helps explain this subject – “sort the head out first”. This is very true, you might be training well and even eating well, but if you lack focus, drive and motivation then all your efforts are wasted. The brain is the central governor and it not only controls how we think and feel but it controls all the other physiological processes such as metabolism, digestion and immunity. There are a collection of chemical messengers in the brain know as neurotransmitters which are responsible for co-ordinating all the neurological signals which make the brain function. A commonly known neurotransmitter is Serotonin which affects mood, sleep and appetite. Another is Dopamine which affects focus and drive. Amino acids act as precursors for many of these neurotransmitters with Tryptophan being the one for Serotonin production and Tyrosine being the precursor for Dopamine. Those with poor sleep or mood problems could be deficient in Tryptophan which is food found in dairy and nuts.

In summary, this is just a general overview to outline some of the functional affects of the types of food you eat. Hopefully, you can see now why simply treating food as “fuel” has no real bearing on how it governs your health, fitness and performance.

“Food is not just Fuel”

  1. Paul Fielding03-09-2012

    Good article – I race road within the eastern region. This winter i have rally been struggling with motivation and drive. I put this down to now working 7×12 hour night shifts within a six week period. Currently taking st johns wort but dont think it works. What foods would you say i should
    increase to help counteract nightshift work.

    Many Thanks

  2. dom coombs03-09-2012

    Hmmm Growth hormone production doesn’t that fall off a cliff after 35

  3. caroline06-10-2014

    Another great article; Thanks! Maybe do one on why everyone fears carbs (maybe some people are genuinely carb intolerant or is it just messed up hormonal/metabolic pathways?)

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