Background and purpose: The importance of adequate dietary carbohydrate for optimal physical performance has long been recognized, but changes in glycemic index and glycemic load of pre-exercise meal might also influence physical exercise and the pattern of substrate utilization during exercise. The aim of this study was to compare the effect of two meals with high or low glycemic load 3 hour preexercise on exercise performance and glycemic response in female athletes.

Materials and methods: Thirty six non-professional female athletes, aged 19-24 years old were enrolled in a cross-over double-blind randomized clinical trial. Participants in each group received breakfast meal with high or low glycemic load, and 7-day wash out period was determined. Serum glucose and insulin measurements were performed before and after each phase of the intervention. Three hours after ingestion of meal, the subjects ran up to exhaustion in a 20-m shuttle run pacer. 7-days wash out period was determined and then changed the two groups.

Results: The ingestion of a high or low glycemic load meal three hours before exercise did not lead to significant difference in exercise performance. But mean changes in serum glucose and insulin in the group who had a meal with high glycemic load was higher than those who had had meals with low glycemic load.

Conclusion: Consumption of a meal with high glycemic load, three hours before a 20-m shuttle run pacer, increased serum glucose and insulin levels during exercise compared to a meal with low glycemic load.

(Clinical Trials Registry Number: IRCT201508185062N9)