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A balanced diet is the starting point for most people but sportspeople may have specific dietary needs. This reflects their personal energy balance equation. When people become more active they use up more energy so they need to take in more to restore their energy balance. Athletes adjust their diets differently depending on their sport and training/performance schedule.

How much to eat

On average, men need around 2,500 calories (Kcal) a day while women need around 2,000. When athletes are training intensively this may increase to around 5,000 calories a day. To calculate how much energy the body needs, the following equation may be used:

BMR or basal metabolic rate is the amount of energy needed just to keep the body systems working normally.

PAL or physical activity level is the amount of energy needed for any activity (sporting or everyday such as housework).

A big athlete – such as a shot putter or rugby forward – will have a higher BMR. A runner or a cross-country skier will have a higher PAL.

When to eat

Before exercise - eat a meal at least two hours before exercise, to give the food time to digest; include plenty of complex carbohydrates and fluid for hydration.

During exercise - small but regular drinks; glucose-based sports drinks and easily digestible carbohydrates may be consumed in small quantities if the exercise lasts more than an hour.

After exercise - eat carbohydrates within 15 minutes if possible, to restore glycogen levels and drink to replace fluids; carbohydrates and proteins should be eaten at least within an hour of exercise to repair muscles and replenish energy stores.

What to eat – special diets

Carbohydrate loading

Carbohydrates provide energy. The complex carbohydrates – starches – are stored in the body as glycogen and converted into glucose when the body needs more energy.

Carbohydrate loading is a technique used to increase the stores of glycogen in the muscles before an endurance event. About four days before the event, the performer gradually decreases training levels and increases the amount of carbohydrates eaten. Performers such as distance runners and cyclists, triathletes and cross-country skiers use this technique.

High-protein diets

Protein builds tissue, including muscle. Athletes who want to build up their muscle during strength-training sometimes eat high-protein diets. This includes obvious strength-training athletes, such as weightlifters, but also includes endurance athletes who want to repair or prevent torn muscle. The value of high-protein diets is debatable. Athletes do not need much more protein than other people, protein is difficult to digest and it does not automatically turn into muscle – the athlete still needs to do strength-training, which is fuelled by carbohydrates.

Hydration and physical activity

Taking in fluids regularly and maintaining the body's hydration levels is extremely important for sports performers and anyone involved in physical activity.

Lack of fluids (dehydration) has the following negative effects on the performer:

• tires (fatigues) and slows down the performer
• skill level decreases
• loss of motivation
• become thirsty
• (muscle) cramps
• decrease in sweating
• increase in body temperature
• (in extreme cases) death

However, by drinking regularly during exercise, athletes can prevent these declines in concentration and skill level, reduce fatigue, prevent excessive increases in heart rate and body temperature and improve performance.