To race a 10km run, 40km bike and 5km run you need to fuel a moderately hard effort until the end of the bike leg, then have enough left in the tank to keep going as fast as you can during the second, shorter run. This means carbohydrate-based fuelling, while also keeping yourself well hydrated and replenishing electrolytes lost in sweat, particularly sodium.
Increase your normal carbohydrate intake slightly at each meal the day before the race, while keeping fat and fibre low. Have some easily digestible carbs for breakfast, e.g. white bread, instant porridge, rice pudding, banana – make sure you’ve trialled this meal in training. Then take a gel or drink 500ml of sports drink about 30-45mins before the start.
Once you’re on the bike, aim for 15-20g of carbs every 20mins from gels, bars or sports drink, and drink at least 500ml of water with added electrolyte tablets. You could also take a gel in the first 5mins of the second run if you feel you need more.