THE G.I. FACTOR: A HIGH CARBOHYDRATE DIET IS ESSENTIAL FOR PEAK SPORTING PERFORMANCE
A high carbohydrate diet is a must for optimum sports performance because it produces the biggest stores of muscle glycogen. As we have previously described, the carbohydrate we eat is stored in the body in the form of glycogen in the muscles and liver. A small amount of carbohydrate (about 1 teaspoon) circulates as glucose in the blood. When you are exercising at a high intensity, your muscles rely on glycogen and glucose for fuel. Although the body can use fat when exercising at lower intensities, fat cannot provide the fuel fast enough when you are working very hard. The bigger your stores of glycogen and glucose, the longer you can go before fatigue sets in.
Unlike the fat stores in the body which can release almost unlimited amounts of fatty acids, the carbohydrate stores are small. They are fully depleted after two or three hours of strenuous exercise. This drying up of carbohydrate stores is often called ‘hitting the wall’. The blood glucose concentration begins to decline at this point. If exercise continues at the same rate, blood glucose may drop to levels which interfere with brain function and cause disorientation and unconsciousness. Some athletes refer to this as a ‘hypo’ and in cycling it is known as ‘bonking’.
All else being equal, the eventual winner is the person with the largest stores of muscle glycogen. Any good book on nutrition for sport will tell you how to maximise your muscle glycogen stores by ingesting a high carbohydrate training diet and by ‘carbohydrate loading’ in the days prior to the competition. In this chapter we provide instructions for increasing muscle glycogen as well as using the G.I. to your advantage in sport.
It was not until a highly respected British endocrinologist, professor David Jenkins, published the first list of G.I. Values that people began to listen. Now working in Canada, he and his colleagues showed that many foods containing starch gave blood sugar responses almost as high as an equivalent load of glucose. Further research showed that many sugary foods had lower blood sugar rises than starchy foods. In other words, scientists and medical practitioners all over the world had it the wrong way round. Unfortunately, many still do.
*111\42\4*
