For many athletes, the "endurance" battle of triathlon is only the half the battle. The other part of the battle comes from the effort of getting the correct amount of calories. Too many calories and your body will not be able to digest the calories and will cause you to have stomach cramping or other problems. Too few calories and your body will not have enough energy to keep you going throughout the race.
Getting enough calories for your race is key. The way to take in these calories and the type of calories varies very differently depending on the length of the race. For example, in a one hour sprint triathlon, your body will be peaked out most of the time and be burning plenty of carbohydrates very quickly. But because your body has enough of these carbs to burn for around one and a half hours, you should be fine to use an electrolyte solution to stay hydrated.
With an Ironman however, it becomes very different. The athlete will be on the course anywhere from 9 hours to 17 hours and must be fueled for the entire race. Because this race will be raced at a more aerobic effort, it is important to teach your body first to take energy from your body's fat and then from the glycogen.
Nutrition can be a very funny thing and is very individualized for every athlete. What may work for you may not work for your friend. Check out this article on nutrition from 6 Time Hawaii Ironman winner Mark Allen. For more information or any questions, please email Jamie at email@example.com.