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Nutrition and Energy . Sports Nutrition Kevin Browne . Function of Energy . Energy has three main functions in the body, regardless of the age or fitness of a person . What are these? Think. Pair Share Energy maintains important body functions such as breathing and digestion.

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nutrition and energy

Nutrition and Energy

Sports Nutrition

Kevin Browne

function of energy
Function of Energy
  • Energy has three main functions in the body, regardless of the age or fitness of a person.
  • What are these? Think.
  • Pair
  • Share
  • Energy maintains important body functions such as breathing and digestion.
  • Energy is crucial for physical activity and movement - without energy, skeletal muscle cannot contract.
  • Energy is used for growth and repair of muscle and tissues in the body.

For the sports performer, energy demand increases rapidly as soon as they start to train or compete. After exercise, energy demand is still high as muscles and other body systems go into repair mode.

  • It would make sense then to presume that an efficiently fuelled athlete is a well prepared athlete. If the sports performer's diet is rich in the nutrients their body needs to perform, then their body will be allowed to perform to its maximum potential.

the body as heat. It is measured in units of heat called 'joules' or using units of energy called 'calories'.

  • The joule and the calorie are very small amounts of energy so they are usually measured in Kilojoules (KJ) and Kilocalories (Kcal):
  • 1 KJ = 1000 joules
  • 1 Kcal = 1000 calories
  • 1Kcal = 4.2KJ


  • This is the main source of energy for exercise, because it is the nutrient that the body can most easily turn into energy. Carbohydrate tends to be used as a short-term energy solution because it is so readily absorbed, converted and used.
  • Fat
  • This is essentially stored energy and is mainly used as a long-term energy store in the body. While it is very energy rich, it is not readily available and so is not an ideal instant source of energy.


  • This is not an ideal source of energy, because protein is mainly designed for repair and growth. The body has to work hard to convert protein to energy and so this is not an ideal fuel for sport. However, because of Western diets rich in protein, the body sometimes has to use this as an energy source. High intakes of protein can be damaging to the body, and so the sports performer should be encouraged to consume mainly carbohydrate for energy.

Energy intake

  • The recommended number of daily kilocalories for men and women are:
  • Men approx 2,500 Kcals
  • Women approx 2,000 Kcals
  • As a general guide for the majority of sports performers, these kilocalories should be consumed as part of a healthy diet that is made up of the following proportions:
  • Carbohydrate: 55-60%
  • Protein 10-15%
  • Fat less than 30%

Where a sports performer needs to consume more kilocalories because of the demands of their sport, the percentages of daily kilocalories should still be adhered to. By changing these percentages, the function of the body could be affected which will ultimately affect sports performance.

  • For example, increasing protein intake will just mean that the body has to work harder to extract the energy it needs from this nutrient, because even when training very hard, the need for protein is still low and the need for 'digestible' energy (carbohydrate) is still high.
nutrition and sport for body fat
Nutrition and sport: for body fat
  • Fat tends to be seen as the evil nutrient, and yet it should make up 30% of the daily intake of nutrients as part of a balanced healthy diet. However, a diet high in kilocalories can ultimately lead to the body storing excess energy as body fat. For the majority of sports performers' (with the exception of a sumo wrestler) excess body fat does not help sports performance.
  • It is also known that being overweight or obese can have a significant effect on health, and there is evidence to show that diets leading to obesity also lead to serious diseases such as coronary heart disease (CHD).

Recommended ranges of body fat as a percentage of the whole body are used to give sports performers' guidance on what would be classed as a healthy level of body fat.

  • Normally, fat levels are compared to muscle mass levels, because a higher level of muscle mass would normally mean that a person had a lower body fat level and vice versa.
  • This is sometimes called the fat-lean ratio, where lean is classed as muscle mass

Sports performers tend to have a higher lean tissue mass (more muscle compared to fat) and so might be at the lower end of the above scale.

  • To an extent, it could be argued that being a sports performer means that the body is working at the extremes of capability and so could be classed as unhealthy.
  • This is why it might be possible to find athletes' who have very low body fat percentages, it is not necessarily healthy but might be needed for sports performance.
  • Remember though, that body fat percentages below recommended minimum levels can lead to illness, injury and disease.
  • There is also little evidence of any performance benefit when men drop under 8% and women drop under 14% body fat.
measuring body composition
Measuring body composition
  • There are many ways of measuring body composition. Some are very easy to do, while others involve very expensive equipment. There is also a huge difference in the accuracy of each method. The methods below are just a sample, but are the most common.
body weight
  • This method normally uses scales of the type found in bathrooms and fitness centres. While it gives a measure of the total weight of a person, it does not give the percentages of fat, muscle, bone and other substances in the body. This means that a person could gain lots of muscle through training and lose lots of body fat, but their total weight might stay the same. The use of body weight as a way of judging body fat percentage should be avoided if at all possible.
  • Body mass index (BMI)
  • The Body Mass Index is a calculation based on a person's height and weight, and gives a number that can be compared to a population norm for healthy and unhealthy ranges.
  • The method is very useful for the general population, but because sports performers tend to have greater muscle mass, care should be taken when applying this method of measuring body composition to athletes. Usually, sports performers will find that the index shows the person to be unhealthy which is normally untrue.
  • The use of BMI has been questioned by some health professionals because of its inaccuracy, although it can still be a useful tool in certain situations.
bmi calculation
  • To calculate a person's BMI, use the following calculation:
  • BMI = Weight (kg) ÷ Height2 (m)
skinfold analysis
Skinfold Analysis
  • The use of skinfold calliper's to measure body fat is widely used in gyms and at sports clubs. It can be an accurate method of measuring body fat, because it can determine between fat and lean muscle tissue. However, the measurements do need to be taken by someone who is experienced at using the callipers to ensure accuracy. Callipers can also be quite embarrassing for a person, because they involve the subject having to be measured around the torso and arms. Care also needs to be taken with the choice of calliper; cheap callipers' often result in less accurate readings although more accurate callipers may be very expensive.
  • There are a number of different methods of skinfold analysis, with each using different test sites on the body and even varying numbers of test sites.
bioelectrical impedance analysis
Bioelectrical impedance analysis
  • This method of analysing body fat measures the level of resistance of current through the body. Since water conducts electrical current well, those tissues with higher water levels (muscle) conduct electricity better than those with lower levels (fat). By determining the resistance to a very low electrical current, an estimate is made of the percentage of fat in the body.
  • This measurement can be quite accurate, but a person's level of hydration can affect readings. Females may get different measurements at different points of their menstrual cycle due to water retention.
  • There are various types of bioelectrical impedance machines, where some use electrical contacts that attach to hands and feet, while others are built into normal weighing scales so that a person's bare feet rest on electrical contacts to allow a current to be passed through the body.
  • Hydrodensitometry is also known as hydrostatic weighing or underwater weighing, and is considered by most professionals to be the gold standard of body fat measurement.
  • A very large tank of water is used for this test, where a comparison is made between the underwater weight and the dry weight of a person. The residual volume of air in the lungs is also taken into account, because it affects buoyancy.
  • Because fat is less dense than the other tissues in the body, it floats more easily. The more fat a person has, the greater the difference between the dry and wet weights. While this method of measuring is very accurate, not many people have access to the very expensive equipment needed.