title: Preexercise galactose and glucose ingestion on fuel use during exercise.
abstract: OBJECTIVE
  This study determined the effect of ingesting galactose and glucose 30 min before exercise on exogenous and endogenous fuel use during exercise.
  
  
  METHODS
  Nine trained male cyclists completed three bouts of cycling at 60% W(max) for 120 min after an overnight fast. Thirty minutes before exercise, the cyclists ingested a fluid formulation containing placebo, 75 g of galactose (Gal), or 75 g of glucose (Glu) to which (13)C tracers had been added, in a double-blind randomized manner. Indirect calorimetry and isotope ratio mass spectrometry were used to calculate fat oxidation, total carbohydrate (CHO) oxidation, exogenous CHO oxidation, plasma glucose oxidation, and endogenous liver and muscle CHO oxidation rates.
  
  
  RESULTS
  Peak exogenous CHO oxidation was significantly higher after Glu (0.68 ± 0.08 g.min(-1), P < 0.05) compared with Gal (0.44 ± 0.02 g.min(-1)); however, mean rates were not significantly different (0.40 ± 0.03 vs. 0.36 ± 0.02 g.min(-1), respectively). Glu produced significantly higher exogenous CHO oxidation rates during the initial hour of exercise (P < 0.01), whereas glucose rates derived from Gal were significantly higher during the last hour (P < 0.01). Plasma glucose and liver glucose oxidation at 60 min of exercise were significantly higher for Glu (1.07 ± 0.1 g.min(-1), P < 0.05, and 0.57 ± 0.08 g.min(-1), P < 0.01) compared with Gal (0.64 ± 0.05 and 0.29 ± 0.03 g.min(-1), respectively). There were no significant differences in total CHO, whole body endogenous CHO, muscle glycogen, or fat oxidation between conditions.
  
  
  CONCLUSIONS
  The preexercise consumption of Glu provides a higher exogenous source of CHO during the initial stages of exercise, but Gal provides the predominant exogenous source of fuel during the latter stages of exercise and reduces the reliance on liver glucose.
authors.affiliation: Research Institute for Sport, Physical Activity and Leisure, Leeds Metropolitan University, Leeds, United Kingdom. J.OHara@leedsmet.ac.uk
authors.forename: John P
authors.initials: JP
authors.lastname: O'Hara
authors.forename: Sean
authors.initials: S
authors.lastname: Carroll
authors.forename: Carlton B
authors.initials: CB
authors.lastname: Cooke
authors.forename: Douglas J
authors.initials: DJ
authors.lastname: Morrison
authors.forename: Thomas
authors.initials: T
authors.lastname: Preston
authors.forename: Roderick F G J
authors.initials: RF
authors.lastname: King
mesh_terms: D000328:Adult; D001642:Bicycling / Q000502:physiology*; D001786:Blood Glucose / Q000378:metabolism; D001835:Body Weight / Q000502:physiology; D002153:Calorimetry, Indirect; D004040:Dietary Carbohydrates / Q000008:administration & dosage / Q000378:metabolism*; D004311:Double-Blind Method; D004435:Eating / Q000502:physiology; D005690:Galactose / Q000008:administration & dosage / Q000378:metabolism*; D005947:Glucose / Q000008:administration & dosage / Q000378:metabolism*; D006801:Humans; D050356:Lipid Metabolism / Q000502:physiology; D008099:Liver / Q000378:metabolism; D008297:Male; D013058:Mass Spectrometry; D018482:Muscle, Skeletal / Q000378:metabolism; D010101:Oxygen Consumption / Q000502:physiology; D055815:Young Adult
chemical_list: D001786:Blood Glucose; D004040:Dietary Carbohydrates; D005947:Glucose; D005690:Galactose