Research indicates that endurance athletes need 150 to 300 calories per hour during activity. Consider factors such as exercise intensity and duration, fitness, and body size when determining how many calories you need to consume on a given day. Through practice in training you’ll be able to come up with an exact number that works for you for this race, and then you can adapt during the event as needed.
Eat or drink your calories just like your car uses gas—steadily not in one big gulp. Take in 50-100 calories along with some plain water every 20-25 minutes during the race or training. Do this consistently. Some people need to set their watch alarm to remind them to eat at regular intervals.
During exercise or an event, drink 6 to 12 ounces (150 to 350 ml) of fluid every 20 minutes. Personalize this quantity—the recommended amount may be too much or too little for you. Experiment with types and quantity based on stomach comfort, body size, and absorption, and make sure you are taking in plain water in addition to your chosen calories for optimal assimilation of calories from the stomach.