title: Fructose and glucose co-ingestion during prolonged exercise increases lactate and glucose fluxes and oxidation compared with an equimolar intake of glucose.
abstract: BACKGROUND
  When fructose is ingested together with glucose (GLUFRU) during exercise, plasma lactate and exogenous carbohydrate oxidation rates are higher than with glucose alone.
  
  
  OBJECTIVE
  The objective was to investigate to what extent GLUFRU increased lactate kinetics and oxidation rate and gluconeogenesis from lactate (GNG(L)) and from fructose (GNG(F)).
  
  
  METHODS
  Seven endurance-trained men performed 120 min of exercise at ≈60% VO₂max (maximal oxygen consumption) while ingesting 1.2 g glucose/min + 0.8 g of either glucose or fructose/min (GLUFRU). In 2 trials, the effects of glucose and GLUFRU on lactate and glucose kinetics were investigated with glucose and lactate tracers. In a third trial, labeled fructose was added to GLUFRU to assess fructose disposal.
  
  
  RESULTS
  In GLUFRU, lactate appearance (120 ± 6 μmol · kg⁻¹ · min⁻¹), lactate disappearance (121 ± 7 μmol · kg⁻¹ · min⁻¹), and oxidation (127 ± 12 μmol · kg⁻¹ · min⁻¹) rates increased significantly (P < 0.001) in comparison with glucose alone (94 ± 16, 95 ± 16, and 97 ± 16 μmol · kg⁻¹ · min⁻¹, respectively). GNG(L) was negligible in both conditions. In GLUFRU, GNG(F) and exogenous fructose oxidation increased with time and leveled off at 18.8 ± 3.7 and 38 ± 4 μmol · kg⁻¹ · min⁻¹, respectively, at 100 min. Plasma glucose appearance rate was significantly higher (P < 0.01) in GLUFRU (91 ± 6 μmol · kg⁻¹ · min⁻¹) than in glucose alone (82 ± 9 μmol · kg⁻¹ · min⁻¹). Carbohydrate oxidation rate was higher (P < 0.05) in GLUFRU.
  
  
  CONCLUSIONS
  Fructose increased total carbohydrate oxidation, lactate production and oxidation, and GNG(F). Fructose oxidation was explained equally by fructose-derived lactate and glucose oxidation, most likely in skeletal and cardiac muscle. This trial was registered at clinicaltrials.gov as NCT01128647.
authors.affiliation: Department of Physiology, Faculty of Biology and Medicine, University of Lausanne, Lausanne, Switzerland.
authors.forename: Virgile
authors.initials: V
authors.lastname: Lecoultre
authors.forename: Rachel
authors.initials: R
authors.lastname: Benoit
authors.forename: Guillaume
authors.initials: G
authors.lastname: Carrel
authors.forename: Yves
authors.initials: Y
authors.lastname: Schutz
authors.forename: Grégoire P
authors.initials: GP
authors.lastname: Millet
authors.forename: Luc
authors.initials: L
authors.lastname: Tappy
authors.forename: Philippe
authors.initials: P
authors.lastname: Schneiter
mesh_terms: D000328:Adult; D001786:Blood Glucose / Q000378:metabolism*; D018592:Cross-Over Studies; D015444:Exercise / Q000502:physiology*; D005632:Fructose / Q000378:metabolism / Q000494:pharmacology*; D005943:Gluconeogenesis / Q000187:drug effects*; D005947:Glucose / Q000378:metabolism / Q000494:pharmacology*; D006801:Humans; D019344:Lactic Acid / Q000378:metabolism*; D008297:Male; D010084:Oxidation-Reduction; D010101:Oxygen Consumption; D016037:Single-Blind Method
chemical_list: D001786:Blood Glucose; D005632:Fructose; D019344:Lactic Acid; D005947:Glucose