Fuel for Long Races
The longer the event is, the more critical race-day nutrition is to your performance. For competitions lasting less than about an hour little is needed other than water. As the duration of the event extends beyond one hour carbohydrate and fluids become increasingly important. For events longer than about six hours refueling the body is often as important to success as how fit and rested you are.
So what should you take in during a long race in order to maintain your intensity at a high level for the duration? The dilemma you face is deciding how to balance intensity against fuel. For example, if you go slowly enough (such as casually walking a marathon) you can eat and drink almost anything you want and your gut will process it. Want a greasy hamburger with french fries and a beer? No problem! But the faster you go the less your gut will be able to process so the more carefully you must choose your fuel. The reason for this is that the body has several demands being placed on all systems and there is competition for the precious resources which are delivered typically by the blood. For example, the muscles are demanding oxygen and carbohydrate to continue contracting at a high rate. At the same time your body is building up heat and trying to shed it. How does it do that? It shunts blood to the skin where it releases heat into the surrounding air thus cooling you off a bit. If you are taking in food, whether liquid or solid, the stomach and intestines are also requesting blood to process and transport the fluids and fuel. And there are other systems also demanding blood. So it's no wonder that athletes often experience GI problems of various types during long, endurance events. There simply aren't enough resources to go around, and given the choice the body prefers to use the blood to cool you and keep the muscles going. The gut is of secondary importance.
So your challenge in preparing for a long race is to determine what it is your gut can best handle at the pace you will be racing. The faster you go, the more this fuel source should be in liquid form since that is the easiest to process in the gut. Solid food requires water to dilute it so that it may be digested. Guess where most of that water comes from if you don't drink enough. The blood.
Your training while building up to a long race must include some long workouts done at race effort. Not only are you trying to become more fit by doing these but you should also be experimenting with fuel types to see what is going to work best for you on race day. Then, when race day finally arrives, you must stick with the pacing and refueling plan developed in training. I often hear athletes who DNF with a complaining gut say, "But it worked for me in training!" So something changed from the workouts to the race. What was it? More than likely it was pacing. The athlete simply went out too fast and the body couldn't deal with all of the demands placed on it. So the stomach "shut down."
It never ceases to amaze me at how important pacing is to long-distance, steady-state events and how little athletes do to pace themselves appropriately, especially early in the race. It's the key to almost everything necessary for success including refueling.