OK, you run marathons. You most probably want to run well - finish in one peice and with a good time. And the occasional personal best would be nice. A good diet designed for marathon runners will help your training and race performance no-end.
Running Performance and Hitting the Wall
The supply of energy to the muscles is vital. As long as carbohydrate is available to provide this energy the body will perform at an optimum level. However, the body can only store a limited amount of carbohydrate. As soon as this is depleted the performance will start to deteriorate.
This deterioration eventually leads to a situation where you 'hit the wall'. A slowed pace is accompanied by dizziness, light-headedness and muscle pain. For some marathon runners this pain and discomfort can be so intense as to cause them to drop out of the race.
Carbo-loading and the 'wall'
Carbo-loading, or carbohydrate loading is a strategy employed to maximise the amount of glycogen in the body. There are a number of different methods and variations of carbo-loading. The main, and widely followed method, is where you increase the level of carbohydrate intake to approximately 70%, particlulalry in the last month before a marathon. Food to choose that are good forms of carbohydrate include pasta, bread and rice. If successful, carbo-loading will prevent runners from hitting the wall.
Marathon runners do not require to alter their protein consumption. Although considerable demand is put on muscles during races (and training) a properly balanced diet should contain sufficient protein to meet your needs.
Further, current evidence suggests that protein and amino acid supplements will provide no benefit for runners.
It is important to keep fat intake low and ensure that body fat stays within reasonable limits. Most good runners have a low body fat content - 15-18% for men and 25-30% for women. Above these values excess fat is simply extra weight, that will result in the body requiring greater effort to cover the same distance. Consequently, performance will fall.
As with protein, it is important to eat enough fat as part of a balanced diet. Fat can provide up to half the energy needed during a long run. At low speeds fat is used as the main source of energy. This switches over to carbohydrate when you run faster, but there may still be an energy demand in the form of fat.