Sporting performance and food

The link between good health and good nutrition is well established, and interest in nutrition and its impact on sporting performance is now a science in itself. Whether you are a competing athlete, a weekend sports player or a dedicated daily exerciser, the cornerstone to improved performance is a nutritionally adequate diet.

Daily requirements
The basic training diet should:

• Provide enough energy and nutrients to meet the demands of training and exercise.
• Include a wide variety of foods like wholegrain breads and cereals, vegetables (particularly leafy green varieties), fruit, lean meat and low fat dairy products.
• Enable the athlete to achieve optimal body weight and body fat levels for performance.
• Promote a quick and full recovery after exercise.
• Provide adequate fluids to ensure maximum hydration before, during and after exercise.
• Consider the short and long term health of the individual.

The athlete’s diet
An athlete’s diet should be similar to that recommended to the general public, with energy intake divided into:

• More than 55 per cent from carbohydrates
• About 12 to 15 per cent from protein
• Less than 30 per cent from fat.

Athletes who exercise strenuously for more than 60 to 90 minutes a day may need to increase the amount of energy they get from carbohydrates to 65 to 70 per cent of energy intake. The World Health Organization states that athletes can consume up to 35 per cent of energy from fat without compromising performance. Some sports nutritionists suggest that extra fat in an athlete’s diet may improve performance for endurance events; however, this is not widely recommended or practised.

Carbohydrates
Foods rich in unrefined carbohydrates, like wholegrain breads and cereals, should form the basis of the diet. More refined carbohydrate foods, such as white bread, jams and lollies, are useful to boost the total intake of carbohydrate. During digestion, all carbohydrates are broken down into glucose, which is the body’s primary energy source. Excess glucose is converted into glycogen and stored in the liver and muscle tissue. Once glycogen stores are full, the vast majority of the remaining glucose is used as energy to sustain the body. Very little glucose is converted to fat, and this is only evident in extreme circumstances.

Glycogen
Glycogen is the most important energy source for the body during exercise.
When you exercise, the glucose in the blood is used as an energy source. The body converts the stored glycogen back into glucose to fuel the exercising muscle tissue and other body systems. Athletes can increase their stores of glycogen by regularly eating high carbohydrate foods. This is important for athletes who exercise strenuously for more than 60 to 90 minutes daily.

If carbohydrate in the diet is restricted, a person’s ability to exercise is compromised because there is not enough glycogen kept in storage. This can result in a loss of protein tissue (and muscle) because the body will start to break down muscle tissue to meet its energy needs. There may also be a loss of essential electrolytes like potassium in the urine.

Glycaemic index
The glycaemic index (GI) ranks carbohydrate-rich foods based on their rate of digestion and absorption. Moderate to high GI foods can efficiently deliver carbohydrate to the body during exercise and recovery. This is why they are increasingly used by sports people. However, the bulk of the carbohydrates consumed in the diet should have a low GI.

The type and timing of food eaten should be tailored to maximise the performance of the particular sport in which the individual is involved.

Pre-event meal
A high carbohydrate meal three to four hours before exercise is thought to have a positive effect on performance. A small snack one to two hours before exercise may also benefit performance. Some people’s blood glucose levels may react negatively to eating close to exercise – it varies between individuals.

The pre-event meal should be easily digestible, high carbohydrate, low fat, low fibre and known not to cause gastrointestinal upset. Examples include fresh fruits and juices, muesli bars (without the chocolate coating), bread, toast, cereal with low fat or skim milk. Contrary to popular belief, consuming sugary foods or drinks just before a sporting event doesn’t boost your energy levels.

Eating during exercise
If exercise lasts longer than 60 minutes, it might be a good idea to eat some carbohydrate during exercise to top up blood glucose levels and delay fatigue. Low fat and low fibre food choices of a high GI, such as lollies (without chocolate) and sandwiches made with white bread, are ideal. Sports drinks and very diluted cordial or fruit juice deliver both carbohydrate and fluid to the body.

Eating after exercise
To top up glycogen stores after exercise, eat carbohydrates with a moderate to high GI in the first half hour or so after exercise. This should then be followed by foods high in carbohydrate, with a low GI.

Protein
Protein is an important part of a training diet and plays a key role in post-exercise recovery and repair. Protein needs are generally met by following a high carbohydrate diet, because many foods – especially cereal-based foods – are a combination of carbohydrate and protein.

The amount of protein recommended for sporting people is only slightly higher than that recommended for the general public. For example:

• General public and active people – the daily recommended amount of protein is 0.75 grams per kilogram of body weight (a 60kg person should eat around 45g of protein daily).
• Sports people involved in non-endurance events – people who exercise daily for less than 60 minutes, should consume between 0.75–1.0 grams of protein per kilogram of body weight per day.
• Sports people involved in endurance events and strength events – people who exercise for longer periods (more than one hour) or who are involved in strength exercise, such as weight lifting, should consume about 1.24 to 1.7 grams of protein per kilogram of body mass.

Dietary surveys have found that most athletic groups comfortably reach and often exceed their protein requirements by consuming a high energy diet. Despite this, protein and amino acids (the building blocks of protein) are popular nutritional supplements.

Amino acids and supplements
Many people believe that additional protein, or even specific amino acid supplements, will provide extra benefits for athletes involved in intense training. This is not the case. Dietary protein supplements are not likely to provide any benefit. In fact, too much protein can be dangerous to short and long term health. It can:

• Overwork the kidneys and make them susceptible to kidney failure
• Compromise bone density
• Lead to weight gain if food choices are also high in fat.

Vitamin supplements
A well planned and nutritionally adequate diet should meet an athlete’s entire vitamin and mineral needs. Supplements will only be of any benefit if your diet is inadequate or you have a diagnosed deficiency, such as an iron or calcium deficiency. There is no evidence that mega-doses of vitamins can improve sporting performance.

The indiscriminate use of vitamins and mineral supplements is potentially dangerous and they should not be taken without the advice of a qualified health professional. Dietary imbalances should be rectified by analysing and altering the diet, rather than by using a supplement or pill.

Water
Dehydration can impair athletic performance and, in extreme cases, can lead to collapse and even death. Drinking plenty of fluids before, during and after exercise is very important. Don’t wait until you are thirsty.

Following exercise, you should drink 500ml of water for every 0.4 to 0.5kg of weight lost during exercise. Fluids are especially important in warm and humid conditions. Water is the preferred fluid; however, sports drinks may be useful in ultra-endurance events (greater than 90 minutes) or when a quick recovery is necessary.

If you prefer taking commercially prepared sports drinks, make sure that they are low in sodium (no more than about 30mmol per litre). Sodium can interfere with glucose getting into the cells and may make dehydration even worse.

Using salt tablets to combat muscle cramps is no longer advised; it is lack of water not sodium that affects the muscle tissue. Persistent muscle cramps might be due to zinc or magnesium deficiencies.

Where to get help

• Your doctor
• An accredited practising dietitian, contact the Dietitians Association of Australia

Things to remember

• Good nutrition can enhance sporting performance.
• Carbohydrate should form the basis of the diet.
• A diet high in protein isn’t generally needed or recommended, since it can hinder performance, impair kidney function and compromise bone integrity.
• Athletes can increase their stores of glycogen by regularly eating high carbohydrate foods.

You might also be interested in:

• Healthy eating tips.
  
• Water - a vital nutrient.
  
• Weight loss and carbohydrates.
  

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This page has been produced in consultation with and approved by:

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Deakin University - School of Exercise and Nutrition Sciences

Fact sheet currently being reviewed.
Last reviewed: November 2009

The information published here was accurate at the time of publication and is not intended to take the place of medical advice. Please seek advice from a qualified healthcare professional.

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