Updated: Dec 22, 2019
"The appropriate foods eaten in the appropriate quantities with the appropriate hydration to fuel optimal training, recovery and performance of a given athlete in their given sport."
Sports nutrition considers both the requirement for energy to fuel the muscles, and the micronutrients to support efficient energy metabolism, immune and antioxidant function, bone health, and muscle recovery and hypertrophy.
Fuelling appropriately should not just be a focus for the elite athlete. The gym bunny athlete and weekend warrior athlete should also consider how they eat to support their activity, and the activities they want to continue to be able to do for a long time to come. Fueling appropriately supports each one of us in living our best life!!
This post summarizes some of the key principles of sports nutrition. It is intended to give a flavour of the things we should all be thinking about, but by no means is an exhaustive list. The detail will be addressed in future posts!!
To fuel activity, the food we eat is converted to adenosine triphosphate (ATP), the energy currency of our cells. When ATP is broken down, the energy released can be used to drive the contraction and relaxation of our muscle cells.
The first question of energy is ‘how much’, i.e. how many calories should you be eating to fuel your activity?
If you eat more calories than you expend, you gain weight. If you eat fewer calories, you lose weight. However, even if weight is stable, your optimal energy intake may not be the one you are currently eating. Why? First, because if you are undereating they may not be able to train and perform as hard, thus reducing your energy output compared to what you are capable of. Second, chronic undereating results in metabolic adaptation. This is where the body conserves energy by reducing energy output in non-exercise activity and metabolism – including simply fidgeting less!!
You can estimate how much energy you need based on your age, gender, height, weight and activity level, and then optimise this through trial and error – if you increase or decrease calories compared to the estimate, what is the impact on bodyweight, performance and recovery?
Protein, Fats and Carbohydrates
Beyond total calories, how athletes split their total calories across protein, fats and carbohydrates is also important. The way these three macronutrients are metabolized to release energy differs, and this has an impact on their suitability as the fuel for different exercise intensities and durations, and therefore different sports.
Carbohydrate is the primary fuel for moderate to high intensity exercise, and we typically have enough stored carbohydrate to fuel such activity for up to 2 hours. Fat can fuel lower intensity exercise, and for a lot longer because we typically have much larger fat stores than carbohydrate stores. Therefore typically the longer the duration of exercise the greater the role for fat, and the shorter or more intense the exercise the greater the need for carbohydrates.
We can also use protein as fuel, however as we need our protein to maintain, repair and grow our body tissue, we will usually only turn to protein as a fuel source when we exhaust our other fuel supplies. Using protein as fuel typically involves breaking down muscle to release the protein … something you are very much going to want to avoid doing as an athlete who needs their muscle to be able to train and perform optimally! Therefore it is important to ensure adequate intake of carbohydrates in particular to avoid the use of protein in exercise (we will discuss low carbohydrate high fat diets, such as the ketogenic diet, and the adaptation to exercise in a later post!).
This will be the focus of my next post, which focusses on the energy systems of the body, however I still want to highlight here that timing of food intake is also important! Specifically, timing of carbohydrate intake as we have only about 2 hours worth of stored carbs (glycogen) in the body. Timing of fat intake for energy is not typically a concern, as the fat used for energy is typically harnessed from fat stores, which most of us have enough of to keep us going longer than we would want to exercise for in a single session …!
In short, athletes should ensure they eat enough carbohydrate before exercise to ensure that our glycogen levels are as high as they can be. For athletes about to undergo an intense training session that will seriously test their glycogen stores, it is advised to consume 2.5g/kg bodyweight in carbs 2-4 hours before undertaking exercise. This is to enable the consumed carbs to get to the liver and muscles as glycogen, and ensure stable blood glucose levels by the time the exercise commences. The topic of fasted exercise is a controversial one – the ability to perform to your highest capacity when fasted will depend on any factors, including how loaded your glycogen stores are from your last meal, how intense and long your exercise session is, and how adapted you are to fasted training. This is a complex topic, but one I hope to explore in a later post!
To maximally refuel our liver and muscle with glycogen after exercise, we should also eat 1g/kg bodyweight in carbohydrate within 2 hours of finishing exercise – when glycogen levels are depleted in exercise you get overcompensation, i.e. glycogen super loading, if you eat carbohydrate within the short timeframe post exercise … and more glycogen in the muscle means you can go harder and faster through the rest of your day and in your next training session.
The macronutrients provide the fuel, but to access the energy in that fuel the body requires micronutrients, i.e. vitamins and minerals. The B vitamins, iron and magnesium are vital cofactors in the machinery to release energy from food, directly or indirectly. Any athlete must be conscious of maintaining levels of these to support optimal energy metabolism, particularly because training increases the turnover of these micronutrients and many are also lost in sweat!
Whilst regular movement is without a doubt beneficial to long term health and immune function, intense exercise does put stress on the body. If the nutrients we need to support the immune system and exercise are in limited supply, both acute and chronically intense training sessions appears to - in some instances - lead to some form of immuno-compromise or reduced tolerance to infection. It is why elite athletes and those with very low body fat may be more susceptible to infection and illness. Inadequate sleep and stress also play a critical role in suppressing the immune system.
So, what should the athlete be conscious of? Key vitamins for immune cell activity and proliferation are vitamins A, C, E, B12, B6 and B1. Vitamins C, E, B1 and B6 cannot be stored in the body and so it is particularly important that these are consumed daily. A diet rich in a variety of vegetables, fruit, nuts and seeds, meat and seafood daily will go a long way to ensuring we maintain appropriate levels of each of these to support immune function.
Physical activity helps build strong bones, in particular exercise that involves short bouts of high intensity strain on the skeleton – such as volleyball or gymnastics or resistance training. The greatest impact is as a kid and teenager when bones are growing, however even as an adult the benefit persists as bone continues to be broken down and rebuilt throughout life.
However, this benefit can only be realized if our bodies have the necessary micronutrients to build those strong bones. Calcium and phosphorous combine to give bones their strength – together they comprise 75% of the total mineral composition of our body, which equates to over 2% of our body mass!! To get these minerals where they need to be and to build strong bones we also need vitamin D, vitamin K and magnesium. This full spectrum of vitamins and minerals is provided by full fat dairy, eggs, red meat, oily fish, oats, nuts and dark leafy green vegetables. The UK government guidelines also recommend that the majority of UK residents (non-special groups) consider supplementing dietary sources of vitamin D with up to 10ug/day vitamin D3 between October and March, the months of least sunlight. This is because whilst vitamin D can be obtained from some food sources (meat, dairy, egg yolks and oily fish) it is not highly available from these; the majority of the vitamin D in our bodies we synthesize ourselves in sunlight. So … minimal sun = minimal vitamin D!
At this point we also need to give some attention to oestrogen in females. Oestrogen is vital in laying down the minerals that make bones strong. If oestrogen is low, the minerals can be stripped from bone making them weak. This is why post-menopausal women are at higher risk of osteoporosis – a condition where bones break easily because they are weak. It is also why, paradoxically, high performing female athletes are often at risk of weak bones. If women are exercising at high intensity and / or undereating to maintain a certain weight for their sport, their menstrual cycle may stop. In other words, their oestrogen levels are chronically low making them at risk of loss of bone mineral density. And if they are undereating they may also not be ingesting sufficient calcium, phosphorous, magnesium etc. to support bone mineral density, regardless of oestrogen levels.
For long term health and athletic performance, and realizing the potential benefits of exercise on these tissues, it is vitally important to fuel for bone health!
Muscle performance, recovery and hypertrophy
Muscles of course power our movement. For an athlete to perform, their muscles must perform! To get faster and to get stronger, muscular adaptation and / or growth must occur.
The ability to generate power comes principally from the ability to produce the energy to drive the muscles to work, and the structure and size of the muscle.
The fuel to produce energy we have already discussed. The machinery to produce the energy is a detailed topic for another time, however it is worth noting that athletes should be conscious of consuming sufficient phosphorous, magnesium and the full spectrum of B vitamins in order to be able to access the energy from food consumed!
Appropriate training drives adaptation and growth of the structure and size of the muscle to enable better performance … if the substrates for this are available. By this, primarily, we mean if the amino acids to build muscle protein are available!
The amount of protein required in the diet varies depending on the sorting discipline of an athlete, with those that require greatest muscular power and involve greatest muscle damage and wear and tear unsurprisingly requiring the highest amount of protein per kilogram of bodyweight. Athletes playing interval sports such as football are recommended to consume up to 1.6g / kg bodyweight, which is approximately twice that of the general population. Those athletes undertaking resistance training and sports are recommended to consume 1.6-2g / kg bodyweight!!
There is also increasing evidence that increasing protein intake up to 3g / kg bodyweight can help to preserve muscle mass when losing weight, i.e. when in caloric deficit. This is likely because this ensures that sufficient protein is available to maintain – and even grow – muscle protein even if some of the protein ingested is used as fuel in the absence of other substrates.
Timing of protein intake is also important to maximise muscle recovery and potential adaptation and hypertrophy. Muscle damage and activation of growth pathways occurs during and immediately after exercise. It is therefore recommended that within 60 minutes of moderate to intense training athletes consume at least 15-25g of complete protein, i.e. containing all essential amino acids.
Water in your body is like the oil in a car. It helps everything work properly – from helping carry things in the blood, to lubricating joints, removing waste, being the environment for your body’s chemical reactions … the list goes on!
Extreme dehydration is obviously fatal, and even mild dehydration negatively impacts a person’s mood, energy levels and mental function. Research has shown that women have difficulty concentrating and suffer fatigue, and men experience a decline in mood and mental ability (ability to reason, learning and short term memory). Given that this happens with just 1.5% dehydration and we don’t typically feel thirsty until we are 1-2% dehydrated, it is highly likely each of us has suffered this more than once.
By the time hydration has fallen 2-3% the blood starts to thicken, putting a strain on the heart and cardiovascular system as it must pump harder to push the same blood volume around the body. Combine this with an intense bout of exercise where your heart is already needing to work hard to pump blood to rapidly deliver nutrients and remove waste from your muscles and you can see how dehydration impacts performance.
Outside of bouts of physical exercise, straight up water is a great way to stay hydrated – as a rough guide, drinking 1ml for every kcal you burn should be enough or, more simply, enough so that your pee is clear or very pale!!
Within exercise, where you are using water at an accelerated rate to drive metabolic reactions, plus losing it in sweat to cool the body and need to rehydrate rapidly, drinking pure water may not actually rehydrate you fast enough! Ideally you want to be consuming fluids that are just a slightly lower concentration to the blood (i.e. has sugar and salts dissolved in it) and specifically containing sodium to help transport the water into the blood and body tissues. This will help the water you drink get to the blood and tissues that need it the fastest! This is the design of sports drinks and electrolyte tablets. Within exercise you want to aim to ingest 1.5x the fluids you are using and losing – this obviously involves some estimation, but an extra 0.5-1 litre per hour of exercise is often taken as a rough guide for your ‘average’ individual.
And finally, we can’t talk about sports nutrition without mentioning supplements. There are many on the market. Some are backed by robust science, whereas the science behind others can be politely described as ‘shaky’ and less politely as ‘utter nonsense’! Of the most popular on the market, those that have been shown to have an impact on athletic performance in broad populations include caffeine, creatine, sodium bicarbonate and whey. There are others that have been shown to benefit more narrow populations. The subject is too vast to address in detail here, but I will address the pro’s and con’s of a number of popular supplements in future posts. For now, I recommend doing your research and speaking to a professional before you start supplementing. And – most importantly – remember the key word is ‘supplement’; they should not be used to replace an appropriate healthy and balanced diet.
Sports nutrition is a vast field with much to consider. However it need not be overwhelming. The basic principles are that you must eat enough to sustain your activity in your chosen sports, and must focus on doing this by eating a variety of unprocessed protein, fat, starchy carbohydrate, fruit and vegetable sources. Ask yourself: do you lack energy? Are you regularly falling sick? Do you have trouble sleeping? Do you regularly get stomach pain? If the answer is yes, as well as analysing the rest of your lifestyle, analyse your nutrition to determine if this could be a causal factor.
Check back in for discussion on specific areas in future weeks!
McArdle, W, Katch, F, Katch, V. Exercise Physiology, Energy, Nutrition and Human Performance. 8th Edition. Wolters Kluwer Health, Philadelphia, USA. 2015.
Wilmore, JH, Costill, DL. Physiology of Sport and Exercise. 3rd Edition. Human Kinetics Publishing. 2005.