A low glycemic index meal before exercise improves endurance running capacity in men.

Plain Language Summary

Carbohydrate loading before exercise is thought to improve exercise performance. However high carbohydrate meals suppress fat metabolism which is important for energy production during prolonged exercise. A low glycemic index (GI) meal consumed 3 to 4 h before exercise is therefore often adopted by sports people. This randomised cross over trial with a wash out period investigated the effects of ingesting a low GI meal or high GI meal 3 hours prior to exercise on endurance running capacity in 8 male recreational runners. The average running time during the low GI trial was significantly longer than high GI trial. Fat oxidation rates were higher during exercise after the low GI meal than after the high GI meal. The authors speculate that subjects began exercise with a higher muscle glycogen concentration after the high GI trial than in the low GI trial and consequently may have used more glycogen during prolonged exercise. In the low GI trial the lower rate of glycogenolysis and higher rate of fat oxidation may have allowed a more rapid “up-regulation” of fat metabolism that was sufficient to support energy expenditure for longer than during the high GI trial. In summary, ingestion of a low GI meal 3 h before exercise resulted in a greater endurance capacity than after the ingestion of a high GI meal.