The effect of high and low glycemic indexed breakfast on cognitive functions after exercise

The glycemic index (GI) value of a meal is important due to it its effect on physical performance during exercise. In addition, studies have been conducted in recent years to show that the value of GI may affect cognitive performance. This study was carried out to investigate the effect of GI value of meal before exercise on cognitive functions and haemodynamics of the brain. 10 healthy male athletes (between the ages of 18 and 22) voluntarily participated to the study and they consumed different types of breakfast with same energy, carbohydrate, protein and fat content but different (low–LGI and high–HGI) glycemic index (GI) values on different days. The effects of different GI breakfast on glycemia were measured. After 90 minutes from breakfast, an 30minute submaximal exercise in the cycling ergometer was performed. Just before and immediately after the exercise "3 Back Test", which measures working memory was used as cognitive function test and the effects on brain hemodynamics (oxyhemoglobin level) during the test were examined by "Functional Near Infrared Spectroscopy (fNIRS) Method". HGI breakfast, resulted in a significant increase in blood glucose both before and after exercise levels compared to LGI breakfast. There was no difference between the LGI and the HGI breakfasts in the "3 Back Test" results both before and after the exercise. In the results of the "3 Back Test" performed after the exercise, the correct response percentage increased after the exercises and the response time to the correct responses decreased. Although, both of these GI values were not statistically significant, it was suggested that exercise had a positive effect on cognitive performance. But it is not statistically significant. On the other hand, an increase in the hemodynamics of the brain was observed during all cognitive tests. It is unclear whether the alternating glucose requirement during cognitive tasks has an effect on brain blood flow change. However, the increase in the level of oxyhemoglobin, after exercise compared to the before exercise; was found to be lower on the day of the HGI breakfast and higher on the day of the LGI breakfast. This suggests that the GI level may be related to the need for less blood flow more effectively to meet the glucose requirement of the brain caused by cognitive overload. But this effect was not statistically significant. Keywords: glycemic index, athlete, cognitive function, working memory