Effect of a Carbohydrate Mouth Rinse on Plasma Glucose and Plasma Insulin during a 40‐km Cycling Time Trial

Abstract

Rinsing the mouth with a carbohydrate solution, without ingesting, improves exercise performance of up to an hour in duration. Performance gains are attributed to the activation of brain regions associated with motivation and motor control. In addition to this neural response, a hormonal cascade may also be present, and include a cephalic‐phase insulin response from oral carbohydrate recognition.PURPOSEThe aim of this study was to examine whether exercise performance gains achieved through a carbohydrate mouth rinse are the partial result of a cephalic‐phase insulin response from oral carbohydrate recognition.METHODSEight trained, competitive cyclists [age (mean ± SEM) = 24 ± 2 y; VO2max = 64.5 ± 2.8 ml/kg/min] completed three simulated, 40‐km time trials comprised of a familiarization trial, carbohydrate mouth rinse trial (CHO) and placebo trial (PLA). Mouth rinse was administered prior to onset of exercise, and every 5‐km throughout exercise. During CHO and PLA trials, plasma glucose and plasma insulin samples were obtained immediately prior to mouth rinsing procedures. Metabolic data and cycling time were collected throughout the exercise session. CHO oxidation rates were calculated based on the equation: g/min = 4.210 VCO2 – 2.962 VO2, while fat oxidation rates were calculated based on: (g/min) = 1.695 VO2 – 1.701 VCO2 (Jeukendrup 2005).RESULTSTime to completion was faster for CHO (67.1 ± 1.1 sec) compared to PLA (67.9 ± 1.0 sec). Plasma glucose did not differ between conditions (p = 0.801) and held steady throughout exercise; additionally, respiratory exchange ratio was not statistically different between conditions (p = 0.081). There was no change in plasma insulin either within trials or between trials (p = 0.638). CHO oxidation rates were not statistically different (p = 0.06) between the CHO (3.43 ± 0.80 g/min) and PLA (2.98 ± 0.18 g/min) groups; fat oxidation rates were not statistically different (p = 0.10) between the CHO (0.59 ± 0.09) and PLA (0.76 ± 0.06) groups.CONCLUSIONSRinsing the mouth with a carbohydrate solution prior to exercise and after each 5‐km interval improved 40‐km time trial performance. This finding shows that improved exercise performance occurs independent of changes in plasma glucose, plasma insulin, RER, or substrate oxidation rates. These findings build on previous research to support the notion of a CHO mouth rinse having primarily a neurological response (Chambers 2009), and not acting via a cephalic‐phase insulin response, in order to improve exercise performance.Support or Funding InformationIndiana University – School of Public Health Student Research Grant Award ‐ March 2016 ($1000)BK Betty Stevens Award (UF funding for trip to Experimental Biology 2017)