Nutrition, from food, provides the energy an individual needs for exercise; eating the right food at the right time gives the body the fuel it needs for optimum performance and recovery. During exercise, fluid is lost through perspiration and rapidly exhaled air, so an adequate intake of fluids is essential to avoid dehydration and the resulting strain that this places on the body. The choice and timing of drinks are also important considerations.
Certain foods and fluids consumed at the right time can enable people to exercise efficiently and to recover quickly afterwards.
ENERGY FROM FOOD
The major energy providers are fats and carbohydrates. Energy is provided by protein only towards the end of a prolonged exercise session, such as running a marathon. Carbohydrates are stored in limited quantities in the muscles and liver in the form of glycogen. When glycogen stores run out, fatigue sets in. Fat, another major fuel, is stored under skin, as adipose tissue, and around internal organs. Aerobic exercise, such as walking or jogging, burns mainly fat for energy, along with some glycogen. Anaerobic exercise, such as sprinting, burns more glycogen and less fat. The fitter a person is, the more her muscles use fat rather than glycogen for fuel. The longer and harder a person has exercised, the more glycogen is used and the longer it takes the muscles to rebuild their reserves. This is partly why it is so important to take rest days, especially when first embarking on an exercise programme. Experienced exercisers are able to replenish their glycogen stores more efficiently than people who are new to exercise.
What to eat
The diet that should accompany an exercise programme is the same diet that should be followed for long-term good health. A balanced diet, based on complex carbohydrates, such as wholemeal bread and pasta, brown rice and other grains and cereals and potatoes, about five servings of fruit and vegetables a day, pulses, fish, nuts, low-fat dairy produce and olive oil rather than butter, is considered to be ideal for health and provides large amounts of complex carbohydrates. Intake of red meat and full-fat dairy produce should be reduced, and cakes, biscuits, crisps and sweets should be only occasional treats.
In order to ensure adequate stores of glycogen for exercise, it is essential to eat enough complex carbohydrates. Studies have shown that people who eat a high-carbohydrate diet can exercise faster, more intensively and almost three times as long as people who eat a low-carbohydrate diet. Endurance athletes or those training for strength need extra protein in their diet.
When to eat
Most people need to wait some time (anything up to 2 hours) before exercising after a large meal – the body needs time to digest the meal, and people often experience a degree of tiredness as this takes place. Swimming, in particular, should be delayed after a meal because of the risk of cramp. However, athletes requiring a fast boost of energy for a sprint may eat a small carbohydrate-rich snack, such as dried fruit, immediately before exercise.
Eating sugary foods immediately prior to exercise may result in hypoglycaemia (a marked decline in blood sugar) as the body tries to deal with excess glucose. Any energy boost offered by sugary snacks is likely to be short-lived and followed by an energy low.
When considering the timing of meals around exercise, bear in mind that food not only provides the energy for exercise, but also enables the body to refuel and recover afterwards. Eating after exercise will help the body to replenish its glycogen supplies (refuelling is twice as efficient during the first 2 hours after exercise). Choose foods with a high glycaemic index, such as rice, bread, noodles or potatoes.
Whenever exercise is taken, fluid is lost through perspiration and exhaled air. De-hydration impairs performance and places a strain on the heart, lungs and circulatory system. It is vital, therefore, to maintain an adequate intake of fluids when exercising.
What to drink
The best fluid for rehydration is pure water. For effective hydration while exercising, the water consumed should be of a relatively cold temperature (5°C / 41°F): at this temperature water is emptied quickly from the stomach and absorbed into the small intestine. Very cold water should be avoided, however.
Electrolyte and carbohydrate drinks produced for athletes can be helpful – their taste may encourage fluid consumption. Electrolyte (also known as isotonic) drinks contain sodium, chloride and potassium, and help to replace the salts lost via perspiration. They are useful if an individual is exercising for long periods in high temperatures and perspiring a great deal. However, salts can also be replaced by adding a light shake of table salt to food (for sodium and chloride) and by eating bananas or drinking diluted tomato or citrus juices (for potassium).
Carbohydrate drinks contain glucose to maintain blood glucose levels and provide extra fuel during exercise. Drinks that contain more than 8 per cent glucose should be avoided because a high-glucose concentration can delay emptying of the stomach.
Experiments on athletes suggest that diluted sports drinks may enhance performance or endurance. However, pure water is sufficient for everyday exercise needs.
When to drink
It is vital to drink enough before, during and after exercise to avoid dehydration. If de-hydration occurs, the kidneys are unable to filter out toxic materials and waste. These toxins build up in the bloodstream and, in extreme cases, can lead to coma. Thirst is a poor indicator of the body’s fluid needs so an individual should drink before she feels thirsty. It is best to take frequent small drinks – ideally about 250ml (1/2 pint) every 15 minutes; if not, as often as possible. It is very important to drink enough when exercising in hot temperatures to replace water lost through heavy perspiration.