What you eat while training for a marathon or other long-distance race determines how much energy you have and how well you do.
Carbohydrates are the main source of fuel for your body. They are stored in the liver and muscles as glycogen. If glycogen stores run low, you'll feel lethargic early in the race and your performance will suffer. The more glycogen you have, the more energetic you'll feel.
For training runs that last 30-60 minutes, your normal diet with adequate hydration is sufficient to maintain energy levels. But as race day approaches and training lasts more than an hour, you'll need food that help you run for two to four hours.
Choose carbohydrates which have a low glycaemic index (GI). This is a measure of a food's ability to raise blood glucose (sugar) levels after it's been eaten. Carbs with a high GI are broken down easily during digestion, allowing glucose to enter the bloodstream quickly. High GI foods include white bread, cornflakes, white rice, honey, fruit juices and sports drinks. These kinds of foods are beneficial if you want a quick burst of energy, so either during or immediately after your run.
But low GI foods break down much more slowly, providing a continuous supply of energy. They should form the basis of your meals as you prepare for the big day. Low GI foods include lentils, kidney beans, chickpeas, spaghetti, yoghurt, pears, apricots, milk and peanut butter.
To lower the overall glycaemic effect of a high GI food, just add a little protein. For example, pair white bread with peanut butter or add low-fat yoghurt/milk to cornflakes.
You may need to 'carbo-load' the week before with bread, rice, pasta, cereals and potatoes. You may find it easier to eat smaller frequent meals.