Eating on the run

With just more than six weeks to go until the Standard Chartered Marathon, those planning on completing the 41.8km should be well into their training programmes.

For first-time marathon runners, an important factor to consider is the type of sports nutrition to use during the event. With so many products on the market, it's difficult to sift through all the claims and descriptions to find the one that best suits you. Regardless of any promises made, only one supplement has earned global respect and acceptance for its benefit to the athlete - and that's carbohydrates.

Fat is the largest source of fuel in the body. Someone who weighs 65kg and has about 17 per cent body fat could use this energy source to sustain very slow exercise for about seven days without ingesting any other food. But for the athlete who's exercising above a moderate level (60 per cent of your maximum rate of oxygen consumption), it takes too long to metabolise the fat.

As a result, they have to rely on another type of fuel: stored carbohydrates. This energy source is stored in the body in two main forms: glycogen in the liver and muscle cells; and glucose (the preferred of the two) in the blood. That same 65kg person mentioned above has about 90 minutes to two hours' worth of this fuel available during moderate exercise.

Since most, if not all, of us will take longer than two hours to complete the marathon, it's essential that we ingest some form of carbohydrate before, during and after exercise to perform at our personal best.

For the past two decades research has shown that ingesting carbohydrates during exercise can improve endurance performance. How does this work? After about 60 minutes of moderate exercise, the glycogen levels in your muscles and liver begin to diminish. At this point there's a shift to blood glucose as the primary fuel source.