The success of your exercise programme depends on the fuel you put into your body. This will affect the intensity and duration of each session. Follow these tips for best performance...

Before exercise
Carbohydrates such as bread, pasta, rice, oats, fruits and vegetables are the body's preferred fuel source, followed by fats. The body breaks these carbohydrates down into glucose to be used as fuel for energy. A small amount is stored in your muscles in the form of glycogen, providing a fast supply of energy during high-intensity exercise such as sprinting. Fats are used mainly for long, low-intensity exercise such as walking. If you run faster, you'll use a higher proportion of glycogen than fat. To maximise your workout, make sure your muscle glycogen levels are high. Low levels can cause tiredness and may reduce the intensity and duration of the session.

Should I eat before training?
Eat a proper meal two-to-four hours before a workout and a light snack one-to-two hours in advance. Most experts recommend eating a low-GI meal to give you sustained energy during your session. In practice, this means eating a portion of carbohydrates, such as two slices of wholemeal bread, brown rice or a baked potato, protein such as chicken, tuna, or eggs and vegetables or a side salad. Although a baked potato has a higher GI than wholemeal bread, adding protein lowers the overall score. The closer you get to your workout, pick a lighter snack. Good choices include a smoothie and a small banana, a handful of dried fruit or an energy bar.

Liquids
Start your exercise session well hydrated. Keep a bottle of water beside you during your workout. Sip the water throughout your session, not just when you feel thirsty, by which time you are probably already dehydrated.

After your workout
The priority is to replace lost fluids. The best way to know how much to drink is to weigh yourself before and after exercise, and drink 20 to 24 fl oz water for every pound lost. You also need to replenish your glycogen stores. The best time to eat is as soon as possible after exercising when your body can store glycogen faster. The post-training meal should include carbohydrate, protein for the repair and recovery of muscle tissue and essential fats—"good" fats found in oily fish such as salmon and mackerel, nuts and seeds and their oils. If you can't manage such a meal within two hours of a workout, eat a snack that includes carbohydrate and protein such as a chicken salad sandwich or a piece of fruit and a yoghurt.

Vitamins and minerals
Exercise increases the need for vitamins and minerals, so you should aim to eat two-to-three fruits and five vegetables a day. This can be achieved by adding a chopped apple to your breakfast, a salad or vegetable soup to your lunch, eating a handful of nuts and seeds as a snack, or having two to three vegetables with your evening meal. Eating a colourful variety of fruit and vegetables ensures you get the full spectrum of vitamins.

GI explained
The glycaemic index (GI) ranks carbohydrates according to how high they raise our blood glucose levels. Low GI carbohydrates such as brown rice and plums release energy slowly, producing only small fluctuations in blood glucose levels. High GI carbohydrates such as cakes, biscuits and white bread release energy quickly, producing large swings in blood glucose levels.

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