Dietary carbohydrates and endurance exercise.

Antecedent diet can greatly influence both substrate utilization during exercise and exercise performance itself. A number of studies have convincingly demonstrated that short-term (three to seven days) adaptation to a low carbohydrate diet results in greatly reduced liver and muscle glycogen stores. While carbohydrate utilization after such a diet is reduced, the limited glycogen stores can severely limit endurance exercise performance. High carbohydrate diets on the other hand expand carbohydrate stores which can limit performance. However, long-term adaptation to a low carbohydrate diet can greatly alter muscle and whole body energy metabolism to drastically limit the oxidation of limited carbohydrate stores with no adverse effect on performance. Glycogen loading techniques can result in supercompensation of muscle stores. Exercise induced depletion of muscle glycogen is the most important single factor in this phenomenon. Following the exercise a low carbohydrate diet for two to three days after which a high carbohydrate diet is eaten seemingly has the same effect on increasing muscle glycogen stores as simply eating a high carbohydrate diet. The form of the dietary carbohydrate during glycogen loading should be high in complex carbohydrates; however, the type of dietary starch that effects the greatest rate of resynthesis has not been investigated. Rapid resynthesis of glycogen following exercise is at least in part due to increased insulin sensitivity. The enhanced glucose transport caused by the increased sensitivity provides substrate for glycogen synthase. How rapidly this enhanced sensitivity returns to pre-exercise levels in humans is uncertain.(ABSTRACT TRUNCATED AT 250 WORDS)