The influence of high carbohydrate diet on plasma glucose and insulin of trained subjects.

In previous studies we have shown that when endurance athletes refrain from daily exercise for three days, they rapidly loose their enhanced insulin sensitivity. This finding suggests that a precompetitive high carbohydrate diet with reduced training might alter plasma glucose and insulin regulation. To test this hypothesis, six long distance runners were recruited to participate in a five-day experiment. During the first two days, the subjects fasted while running 16 km d-1. Thereafter, they consumed 16.3 MJ (3900 kcal) and 539 g carbohydrate per day for three days while remaining inactive. Before and after each portion of this experiment, an intravenous glucose tolerance test (IVGTT) was performed in fasting state. As expected, fasting with exercise induced a considerable deterioration of glucose tolerance, as reflected by lower K value and higher total area glucose during IVGTT. The high carbohydrate refeeding restored glucose tolerance to a level comparable to that observed when subjects maintain their usual life habits. However, while a decrease in insulin sensitivity is observed in subjects inactive for three days, the insulin sparing effect of exercise training is retained if this period of inactivity is preceded by two days of fast accompanied by exercise. These results show that glucose disposal and insulin response to glucose injection are not adversely modified by the precompetitive "glycogen loading" procedure.