The glycemic index (GI) of a pre-exercise meal has been shown to affect substrate oxidation during exercise and may influence exercise performance. Previous research in this area has focused on continuous, moderate intensity exercise. The purpose of this study was to examine the effects of low and high glycemic index (GI) pre-exercise meals on metabolism and performance during soccer-specific intermittent exercise. Thirteen trained male soccer players (22.3 ± 3.3 yrs) participated in four experimental trials in a repeated crossover design. Isocaloric low GI-high protein (lentils), high GI-high protein (potato + egg whites), or high GI-low protein (potato) meals were consumed two hours before a 90-minute treadmill soccer match simulation. A fasted control condition was also employed. Blood and expired gas samples were collected before and during exercise to assess markers of carbohydrate and fat metabolism. The distance covered on five 1-minute sprints (separated by 2.5 minutes of recovery) performed during the last 15 minutes of the match was used to assess performance. Serum insulin concentration at the start of exercise was higher in the high GI-low protein condition compared to all other conditions (p<0.001). During exercise, the rate of carbohydrate oxidation was significantly higher and the rate of fat oxidation was significantly lower in the high GI-low protein condition compared to control (p<0.05). The distance covered on sprints 1 and 2 was significantly greater in the low GI-high protein condition compared to control (p<0.05). The distance covered on sprint 2 was significantly greater in the high GI-high protein condition compared to control (p<0.05). There were no significant differences between conditions for sprints 3-5. Ratings of perceived exertion (RPE) throughout exercise were significantly lower in the low GI-high protein condition compared to both control and high GI-low protein conditions (p<0.05). It is concluded that low GI-high protein and high GI-high protein pre-exercise meals result in small improvements in initial repeated sprint performance compared to fasted control. Performance was not improved following a high GI-low protein pre-exercise meal compared to control, indicating that the increased carbohydrate oxidation and decreased fat oxidation in this condition may have negated any potential performance advantage of carbohydrate consumption. The lower RPE throughout exercise in low GI-high protein compared to control and high GI-low protein indicates a possible beneficial effect of consuming a low GI meal prior to soccer-specific intermittent exercise.

The glycemic index (GI) of a pre-exercise meal has been shown to affect substrate oxidation during exercise and may influence exercise performance. Previous research in this area has focused on continuous, moderate intensity exercise. The purpose of this study was to examine the effects of low and high glycemic index (GI) pre-exercise meals on metabolism and performance during soccer-specific intermittent exercise. Thirteen trained male soccer players (22.3 ± 3.3 yrs) participated in four experimental trials in a repeated crossover design. Isocaloric low GI-high protein (lentils), high GI-high protein (potato + egg whites), or high GI-low protein (potato) meals were consumed two hours before a 90-minute treadmill soccer match simulation. A fasted control condition was also employed. Blood and expired gas samples were collected before and during exercise to assess markers of carbohydrate and fat metabolism. The distance covered on five 1-minute sprints (separated by 2.5 minutes of recovery) performed during the last 15 minutes of the match was used to assess performance. Serum insulin concentration at the start of exercise was higher in the high GI-low protein condition compared to all other conditions (p<0.001). During exercise, the rate of carbohydrate oxidation was significantly higher and the rate of fat oxidation was significantly lower in the high GI-low protein condition compared to control (p<0.05). The distance covered on sprints 1 and 2 was significantly greater in the low GI-high protein condition compared to control (p<0.05). The distance covered on sprint 2 was significantly greater in the high GI-high protein condition compared to control (p<0.05). There were no significant differences between conditions for sprints 3-5. Ratings of perceived exertion (RPE) throughout exercise were significantly lower in the low GI-high protein condition compared to both control and high GI-low protein conditions (p<0.05). It is concluded that low GI-high protein and high GI-high protein pre-exercise meals result in small improvements in initial repeated sprint performance compared to fasted control. Performance was not improved following a high GI-low protein pre-exercise meal compared to control, indicating that the increased carbohydrate oxidation and decreased fat oxidation in this condition may have negated any potential performance advantage of carbohydrate consumption. The lower RPE throughout exercise in low GI-high protein compared to control and high GI-low protein indicates a possible beneficial effect of consuming a low GI meal prior to soccer-specific intermittent exercise.