The Effects of Varying Level of Glucose and Fructose on Brain Activation During Mouth Rinse

Mouth rinsing a carbohydrate (CHO) solution has been shown to activate receptors within the oral cavity that is related to reward and pleasure centres of the brain. This brain activation is linked to enhance endurance exercise performance. However, it remains unclear, whether the caloric content or the level of sweetness of a solution may influence the level of brain activation during mouth rinse. Therefore, the aim of this study was to examine the effects of varying level of caloric content made up from glucose and fructose on brain activation during mouth rinse. Eleven healthy male participants (Age: 21 ± 2 years; stature: 168 ± 7 cm; body mass: 61.4 ± 6.4 kg; and peak rate of oxygen consumption (VO2max): 51.3 ± 2.2 ml.kg.min-1) volunteered to participate in this study. Participants were randomly assigned to perform 6 trials of mouth rinsing. During each trial, participants were asked to rinse a CHO solution for 10 seconds while fMRI was performed. Three sets of caloric-content solutions were prepared. The first set of caloric-content was at 19 kcal/g consisting 6% of glucose and 5.3% of fructose. The second set was 59 kcal/g consists of 18% of glucose and 15.9% of fructose and the last set was 79 kcal/g consists of 24% of glucose and 21.2% of fructose. The neuroimaging results showed that there was no clear trend on brain activation when rinsing with high caloric content of the CHO solution. However, when rinsing a sweeter solution of fructose, a larger magnitude of the insula/frontal operculum region of the brain was activated. The current observation suggests that the level of sweetness and not the caloric-contents potentially be the main determinant of brain activation.