Family doctor

Nutrition is very important in sport, regardless of which sport you do and at what level you take part.

A variety of different nutrients are needed on a daily basis to keep fit and healthy.

A balanced diet should provide the right proportions of:

• carbohydrate
• fat
• protein
• vitamins and minerals
• water
• dietary fibre

Energy is the most important nutritional factor for any form of physical activity. The main fuels used by exercising muscles are carbohydrate and fat. The amount of each of these fuels used depends on the type, intensity and duration of the exercise.

CARBOHYDRATE

Carbohydrate is required for any form of exercise. Small amounts of carbohydrate are stored in the liver and muscles as glycogen. During exercise, this glycogen is broken down into glucose, which, along with fat, supplies the muscle with energy.

In short bursts of high intensity (anaerobic) exercise, such as sprinting, a large amount of energy is quickly required. Glycogen is therefore the main fuel as only it can be converted fast enough. Very little fat is used.

In longer periods of low intensity exercise ( aerobic) such as cycling, swimming, long distance running, glycogen is the main fuel but as these stores are used up, a greater proportion of fat is used. Fat cannot be broken down quickly enough to continually meet a high energy expenditure and therefore, the ability to perform prolonged exercise is related to your body's glycogen stores. Fatigue is a result of low levels of glycogen in the exercising muscles. A high level of glycogen at the start of exercise can delay the onset of fatigue.

BUILDING UP GLYCOGEN STORES

Glycogen stores are built up by the consumption of plenty of carbohydrate foods. For sports people it is recommended that 60 &endash; 70% of your daily energy intake should come from carbohydrates.

Good sources of carbohydrates are bread, cereals, potatoes, rice and pasta. Choosing wholemeal varieties of these foods will also increase dietary fibre.

REFUELLING

Muscle glycogen must be replaced after training; otherwise you will not be able to train to your maximum at your next session.

It can take upto 48 hours for muscle glycogen stores to be replenished; if your diet is low in carbohydrate, it will take even longer! It is also recommended that you should vary heavy and light training sessions to allow muscles to refuel properly.

Suitable high carbohydrate snacks to have after sports are bananas, cereal bars, sandwiches, fresh or dried fruit.

PROTEIN

Recent evidence suggests that sportspeople do have an increased requirement for protein, but the consumption of a balanced diet should meet these requirements.

10-12% of the total energy intake should come from protein; any excess will be converted to and stored as fat or excreted. Excessive amounts can be dangerous.

Protein is only used as a fuel if the carbohydrate and fat are failing to provide enough energy

Good sources of protein are meat, poultry, fish, milk, cheese, yoghurt, eggs, nuts and legumes.

FAT

There is no such thing as a fat-free diet! A certain amount of fat is necessary in the diet for the provision of essential fatty acids, vitamins A, D, E and K; it is also a concentrated energy source.

Fat is mainly stored in the adipose tissues and some is stored in muscle cells.

The remainder of the total energy intake should come from fat.

Trained endurance sportspeople can use fat as an energy source for a longer period of time than an untrained person.

Sources of unsaturated fats: nuts and most vegetable oils

Sources of saturated fats: red meats, whole eggs, whole milk and milk products.

VITAMINS AND MINERALS

Providing a wide variety of foods are eaten, vitamin and mineral intake should be adequate, therefore, supplementation is not necessary.

A diet deficient in vitamin and minerals can compromise sporting performance as they are important in energy metabolism.

FLUID

75% of the human body is made up of water.

Fluid losses during sports can be high and it is vital that these losses are replaced. Dehydration affects performance and is a cause of fatigue. Thirst is a sign that you are already dehydrated.

Water is the best fluid to drink if you are exercising at a moderate intensity for upto 60 minutes. After this, a sports drink containing 4-8g of carbohydrate per 100ml will help to rehydrate as well as providing energy.

A carbohydrate concentration higher than this will slow down the rate of water absorption whilst very high concentrations may lead to stomach cramps and abdominal discomfort.

Try and drink whilst training; approximately 150 to 200 ml every 15 to 20 minutes. Most importantly, start your training thoroughly hydrated!