SPORTS NUTRITION: Fueling our energy system





According to the World Health Organization, nutrition is the intake of food in relation to the body’s dietary needs. Sports Nutrition is defined as the specialized branch of nutrition that studies food with relevance to athletic performance.  In simple terms, manage how food impacts on performance. Sports nutrition has short term and long term effects on the body composition, metabolism and ultimately performance abilities (4). It is very different to personal nutrition. Everybody’s needs and requirements are different. Nutrition must be adapted to the individual and this requires experimenting to suit an individual’s needs, basically a process of trial and error. One size does not fit all in this case, what has worked for someone may not work for you. There are too many ‘experts’ in sports nutrition out on the internet and on social media,  unknowingly providing dietary advice in a way that encourages bad self-image, injury, illness and you do not want that. So, it is important to make sure to take advices from reliable sources and qualified people in the field.

Sport nutrition has grown massively over the last couple of years. We are constantly being bombarded with adverts on the TV, radio, blogs, gyms, internet, peers all guiding us on what to eat and what not to eat, often contradicting each other. We cannot out-train a bad diet, just because we are heading to the gym later that does not mean we can eat all the food we want. If we want to see improvement in our performance or change in our body composition, we must eat appropriately and fuel our body correctly. This is where sports nutrition takes over. There are a lot of aspects to sports nutrition.  It can get overwhelming to people who are new to the area on where should they even start. The sports nutrition article today and in the future will be providing a lot of information. We will cover most of the aspects of sports nutrition and it can get a little scientific but I will try and simplify it as much as I can for you to better understand and use sports nutrition to your advantage.


The diet can provide adequate energy from a wide range of commonly available foods that can meet the carbohydrate, fat, protein and micronutrient requirements of training and competitions. We will discuss supplements at a later stage; however we should try to fulfil all our dietary requirements through diet. That is the goal. Just like how cars needs fuel to function, our body also needs fuel to perform but in this case our fuel is food. You put in the wrong fuel like your bad foods, your body, like the car, will break down. You put in the right fuel, good nutritious foods, your body will be fully functional and at an optimal state.

The essential nutrients for life are the building blocks of good nutrition and are what makes up our food. We need all these nutrients namely carbohydrates, protein, fat, vitamins, minerals, water and fiber to be in good health, should one or more be missing from your diet malnutrition can occur. The three main macronutrients used for energy in the body are carbohydrates, fat and protein. Here is a quick overview of these nutrients when discussing energy systems; however we will talk about them in much detail in later articles.


Carbohydrates are more commonly referred to as carbs. They are found in a wide array of both healthy and unhealthy foods. Carbohydrates also come in a variety of forms, for instances sugars, fibers and starches. Carbohydrate is the primary source of energy that provides the body with glucose, which is converted to energy used to support bodily functions and physical activity. It is the most important fuel for energy. Excess carbohydrates are stored as glycogen in liver and muscles and as fat in the body. Carbohydrates provide 4kcal or 17kj of energy per gram.





The protein intake for sport enthusiasts is higher than that recommended intake for the general population. The primary function of protein is growth, maintenance and repair of tissue and cells. Protein also has enzymatic function since all enzymes are proteins, transport function acting as carriers for other nutrients, hormonal functions, immune function for antibodies and buffering function maintaining pH balance of the blood. Protein is the most satisfying nutrient and delivers a small fuel source for exercise. In the absence of carbohydrate, protein acts as a secondary source of energy providing 4kcal or 17kj per gram.

  • FAT

It is common to think fat should be eliminated from the diet but most people are just misinformed of fat intake in sports nutrition. Some fat in the diet is essential and sports enthusiasts should not follow a fat free diet. Fat has important functions in the body. They are oxidized in the body to provide energy for your cells. They are energy dense providing 9 kcal or 38 kj per gram. They provide essential fatty acids and carry fat soluble vitamins A, D, E and K around the body as well as antioxidants. Fat stores provide insulation to the body by preventing heat loss. They also provide a reserve of energy for the body which is stored as adipose tissue. Fat form part of the structure for brain tissue and layer around nerves. Athletes should aim for the majority of their fat intake to come from unsaturated fats. Omega 3 fatty acids may be of particular interest to athletes due to increased recovery and oxygen delivery.



Energy metabolism can be a little confusing to understand, so we are going to discuss briefly how the macronutrients namely carbohydrates, protein and fat produce energy in the body and how we are going to use the systems to determine exercise. There are 3 main energy systems that are used for physical activity. These 3 systems produce different amounts of ATPs at different rates. These rates of transfer of ATP can be a limiting factor in exercise. (1)

ATP stands for Adenosine Tri-Phosphate which is the energy used by the body in its daily operations and keeping the body alive. ATP is a small molecule consisting of one adenosine molecule and 3 phosphate groups attached.

Energy is released when one of these phosphate groups splits off, reducing the ATP from 3 phosphates to 2 phosphates called ADP (Adenosine Di-Phosphate). ATP is constantly being used up by the body in its biological processes and most of this energy is given off as heat. It is a constant cycle where energy from food provides the ATP which is then broken down by the body to release energy. The energy supply needs to be improved by new sources of fuel as the demand of exercise increases energy needs to meet this increased requirement. Hence, more fuel needs to be broken down; this is where the macronutrients come into place.

  • System 1: ATP-PC

When we are at rest, our energy requirements are met by small amounts of ATP. As we begin to exercise, this energy demand suddenly increases. So to continue exercising ATP needs to be regenerated and this is where ATP-Phospho-Creatine system comes into play. (1)

Creatine is a compound made naturally in the body and combined with phosphate; this system provides energy for a brief period of intense activity such as a short sprint, single jump or maximal weight lift.  This explains why most supplements are creatine based to boost this system; however, it can be obtained from foods as well. High intensity activity can deplete the system within 10 seconds and lower intensity activity can deplete the energy in 3 minutes within the muscle cell. This system can be called a back up to the ATP. This system releases energy very quickly but it is limited. When this energy is depleted, the other energy system will take over.

  • System 2: Anaerobic Glycolysis

This system kicks in as soon as we begin high intensity activity. Glycolysis is the breakdown of glucose to form lactate and consists of a series of chemical reactions that are controlled by enzymes. The system works in the absence of oxygen, hence the term anaerobic. This system uses carbohydrates as fuel in the form of glucose or glycogen. The end product of this energy system is lactic acid. As the lactic acid accumulates, the production of ATP starts declining. The anaerobic glycolysis system has a larger fuel supply compared to ATP-PC system but it does not burn its fuel quite as much or as fast as the ATP-PC system. By 30 seconds of sustained intense activity the majority of energy comes from the anaerobic glycolytic system. At 45 seconds of sustained intense activity there is a second decline in power output and it dominates the system lasting 90 seconds. So for activities like weight training, 400 to 800 m sprint, we will be mainly using the anaerobic glycolysis system. Exercise beyond the 90 second point will then rely on the aerobic energy system as the anaerobic glycolytic system starts to fatigue. (2)

  • System 3: Aerobic metabolism

The aerobic metabolism generates ATP from the breakdown of carbohydrate and fat. Carbohydrates and fats are used to fuel this system and it is done in the presence of oxygen. This system produces energy 20 times more efficiently then the anaerobic glycolysis but it is a lot slower. Most of the energy from this system comes from glycogen stored in our muscles and fats. Fats can only be broken down to produce energy in the presence of oxygen in the aerobic system. When exercising in high intensity, we cannot get enough oxygen to our muscles in turn fat cannot be broken down. So, it is questionable why should we exercise at high intensity if we are not going to break down fat. That is not the case, with high intensity exercising fat will be broken down during the rest periods and after training. Exercising at moderate intensity enables us to get more oxygen in our muscle, so you can break down fat.




This graph represents the energy systems a lot clearly and it puts all the systems explained above into perspective. According to the graph we can see how long the systems kicks in for and how much energy do they give off. At first we will be burning ATP immediately moving into phosphocreatine which will back that up once ATP needs to be regenerated. Following that the anaerobic system kicks in whereby we will be using carbohydrate as energy up until 90 seconds and finally the aerobic system will take over whereby carbohydrates and fat are used as fuel to produce energy.

From this table above we can see the different types of exercise according to the energy system they use along with what is used as fuel by the body. Glycogen mentioned in the table is referred to stored glucose in the body in the muscle and liver. In the aerobic system, the body uses both carbohydrates in the blood and stored glycogen along with fat as a source of fuel for energy production. At moderate to high intensity activity, protein will only be used as a source of fuel only if the body does not have enough carbohydrates, then the body will use protein, glycogen and fat as fuel. However, we do not want to use protein as fuel source and break down muscle mass, that is why carbohydrate intake is so important. 

In the future article we will be talking more about the different factors to consider in sports nutrition. We will cover most of the aspects of sports nutrition as we go along. Should you have any questions (big or small don’t be afraid to ask), you can comment on the post or book an appointment with us, we will be more than welcome to clear your doubts and help.



  1. Energy systems. Canadian Academy of Sports Nutrition.
  2. Anaerobic Glycolysis. Canadian Academy of Sports Nutrition.
  3. Aerobic Glycolysis. Canadian Academy of Sports Nutrition.
  4. Sports Nutrition.



2 thoughts on “SPORTS NUTRITION: Fueling our energy system

    • JHPResolutions says:

      Thank you. Having the correct information in your exercise program makes a difference. Rather consult a professional to get the results that you are looking for. Nutrition and exercise plan can’t be separated.

Leave a Reply

Your email address will not be published. Required fields are marked *