Carbohydrates are the main source of fuel for your body and they're stored in the liver and muscles as glycogen. If glycogen stores run low, you'll feel lethargic - in a race, this means your performance will suffer.

Just as a car needs refuelling with petrol before a long journey, so do your glycogen stores need stocking up before a race. The larger your glycogen stores, the more energetic you'll feel, and the longer you can continue to perform at your best.

Depending on the length of the race, you may need to start loading up on carbohydrates ('carbo-loading') the week before with bread, rice, pasta, cereals, potatoes, fruit and vegetables.

The night before the race, try to eat carbs which are low in fibre - high-fibre carbs fill you up too quickly, and are hard to digest.

It's best to stick with familiar foods before a competition - trying new foods may not agree with your stomach, resulting in 'runners trot'.

Be sure to stay hydrated, too. You need six to eight glasses of fluids (water, diluted fruit juices or isotonic sports drinks) a day, but when you're training you need more.

One way of checking if you're drinking enough is to look at the colour of your urine: if it's pale and colourless, you're hydrated; if it's dark and in small amounts, you're dehydrated.

Pre-race menu suggestion

Breakfast: Fruit juice, oatmeal with raisins and honey, a banana or an apple; milk

Lunch: Turkey salad sandwich, a plum or a nectarine

Dinner: Grilled chicken breast or fish, baked potato, rice or pasta, carrots and peas

Snacks: Fruits and yoghurt; water throughout the day

Don't forget to eat breakfast on race day: a glass of fruit juice or a smoothie, a bagel or toast with jam or cereal with milk. It's a good idea to eat at least a couple of hours before the big race.

Miranda's diary

Breakfast: Toast and fruit or Weetabix, milk

Lunch: Bread roll and chicken or pasta or rice dishes

Dinner: Stir-fried vegetables and meat with rice, or pasta with tomato sauce or pesto

Snacks: Fruit and biscuits

Exercise: An hour of swimming once a week, running 3-4 times a week, cycling once a week, hiking on weekends